@article{HaerterichMatlerDewhurstetal.2023, author = {H{\"a}rterich, Marcel and Matler, Alexander and Dewhurst, Rian D. and Sachs, Andreas and Oppel, Kai and Stoy, Andreas and Braunschweig, Holger}, title = {A step-for-step main-group replica of the Fischer carbene synthesis at a borylene carbonyl}, series = {Nature Communications}, volume = {14}, journal = {Nature Communications}, doi = {10.1038/s41467-023-36251-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-357270}, year = {2023}, abstract = {The Fischer carbene synthesis, involving the conversion of a transition metal (TM)-bound CO ligand to a carbene ligand of the form [=C(OR')R] (R, R' = organyl groups), is one of the seminal reactions in the history of organometallic chemistry. Carbonyl complexes of p-block elements, of the form [E(CO)n] (E = main-group fragment), are much less abundant than their TM cousins; this scarcity and the general instability of low-valent p-block species means that replicating the historical reactions of TM carbonyls is often very difficult. Here we present a step-for-step replica of the Fischer carbene synthesis at a borylene carbonyl involving nucleophilic attack at the carbonyl carbon followed by electrophilic quenching at the resultant acylate oxygen atom. These reactions provide borylene acylates and alkoxy-/silyloxy-substituted alkylideneboranes, main-group analogues of the archetypal transition metal acylate and Fischer carbene families, respectively. When either the incoming electrophile or the boron center has a modest steric profile, the electrophile instead attacks at the boron atom, leading to carbene-stabilized acylboranes - boron analogues of the well-known transition metal acyl complexes. These results constitute faithful main-group replicas of a number of historical organometallic processes and pave the way to further advances in the field of main-group metallomimetics.}, language = {en} } @article{WeiserCuiDewhurstetal.2023, author = {Weiser, Jonas and Cui, Jingjing and Dewhurst, Rian D. and Braunschweig, Holger and Engels, Bernd and Fantuzzi, Felipe}, title = {Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand}, series = {Journal of Computational Chemistry}, volume = {44}, journal = {Journal of Computational Chemistry}, number = {3}, doi = {10.1002/jcc.26994}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312586}, pages = {456 -- 467}, year = {2023}, abstract = {The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.}, language = {en} } @article{WitteArrowsmithLamprechtetal.2023, author = {Witte, Robert and Arrowsmith, Merle and Lamprecht, Anna and Schorr, Fabian and Krummenacher, Ivo and Braunschweig, Holger}, title = {C-C and C-N Bond Activation, Lewis-Base Coordination and One- and Two-Electron Oxidation at a Linear Aminoborylene}, series = {Chemistry - A European Journal}, volume = {29}, journal = {Chemistry - A European Journal}, number = {16}, doi = {10.1002/chem.202203663}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312491}, year = {2023}, abstract = {A cyclic alkyl(amino)carbene (CAAC)-stabilized dicoordinate aminoborylene is synthesized by the twofold reduction of a [(CAAC)BCl\(_{2}\)(TMP)] (TMP=2,6-tetramethylpiperidyl) precursor. NMR-spectroscopic, X-ray crystallographic and computational analyses confirm the cumulenic nature of the central C=B=N moiety. Irradiation of [(CAAC)B(TMP)] (2) resulted in an intramolecular C-C bond activation, leading to a doubly-fused C\(_{10}\)BN heterocycle, while the reaction with acetonitrile resulted in an aryl migration from the CAAC to the acetonitrile nitrogen atom, concomitant with tautomerization of the latter to a boron-bound allylamino ligand. One-electron oxidation of 2 with CuX (X=Cl, Br) afforded the corresponding amino(halo)boryl radicals, which were characterized by EPR spectroscopy and DFT calculations. Placing 2 under an atmosphere of CO afforded the tricoordinate (CAAC,CO)-stabilized aminoborylene. Finally, the twofold oxidation of 2 with chalcogens led, in the case of N\(_{2}\)O and sulfur, to the splitting of the B-C\(_{CAAC}\) bond and formation of the 2,4-diamino-1,3,2,4-dichalcogenadiboretanes and CAAC-chalcogen adducts, whereas with selenium a monomeric boraselenone was isolated, which showed some degree of B-Se multiple bonding.}, language = {en} } @article{LindlLamprechtArrowsmithetal.2023, author = {Lindl, Felix and Lamprecht, Anna and Arrowsmith, Merle and Khitro, Eugen and Rempel, Anna and Dietz, Maximilian and Wellnitz, Tim and B{\´e}langer-Chabot, Guillaume and Stoy, Andreas and Paprocki, Valerie and Prieschl, Dominik and Lenczyk, Carsten and Ramler, Jacqueline and Lichtenberg, Crispin and Braunschweig, Holger}, title = {Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands for Main Group Elements}, series = {Chemistry - A European Journal}, volume = {29}, journal = {Chemistry - A European Journal}, number = {11}, doi = {10.1002/chem.202203345}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312222}, year = {2023}, abstract = {The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe\(_{3}\) and 2-EMe\(_{3}\) (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N\(_{3}\)EMe\(_{3}\)-derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe\(_{3}\) yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe\(_{3}\))\(_{2}\) (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO\(_{2}\) yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C\(_{5}\)Me\(_{5}\)), BBr\(_{2}\)Ar (Ar=Ph, Mes, 2-thienyl), ECl\(_{3}\) (E=B, Al, Ga) and PX\(_{3}\) (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr\(_{3}\) resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution \(^{11}\)B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C\(_{4}\)BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic \(^{11}\)B NMR resonances is linearly correlated to both the degree of twisting of the C\(_{4}\)BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent.}, language = {en} } @article{BachmannHelbigCrumbachetal.2022, author = {Bachmann, Jonas and Helbig, Andreas and Crumbach, Merian and Krummenacher, Ivo and Braunschweig, Holger and Helten, Holger}, title = {Fusion of Aza- and Oxadiborepins with Furans in a Reversible Ring-Opening Process Furnishes Versatile Building Blocks for Extended π-Conjugated Materials}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {63}, doi = {10.1002/chem.202202455}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-293926}, year = {2022}, abstract = {A modular synthesis of both difurooxa- and difuroazadiborepins from a common precursor is demonstrated. Starting from 2,2′-bifuran, after protection of the positions 5 and 5' with bulky silyl groups, formation of the novel polycycles proceeds through opening of the furan rings to a dialkyne and subsequent re-cyclization in the borylation step. The resulting bifuran-fused diborepins show pronounced stability, highly planar tricyclic structures, and intense blue light emission. Deprotection and transformation into dibrominated building blocks that can be incorporated into π-extended materials can be performed in one step. Detailed DFT calculations provide information about the aromaticity of the constituent rings of this polycycle.}, language = {en} } @article{FullWoelflickRadackietal.2022, author = {Full, Felix and W{\"o}lflick, Quentin and Radacki, Krzysztof and Braunschweig, Holger and Nowak-Kr{\´o}l, Agnieszka}, title = {Enhanced Optical Properties of Azaborole Helicenes by Lateral and Helical Extension}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {62}, doi = {10.1002/chem.202202280}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-293671}, year = {2022}, abstract = {The synthesis and characterization of laterally extended azabora[5]-, -[6]- and -[7]helicenes, assembled from N-heteroaromatic and dibenzo[g,p]chrysene building blocks is described. Formally, the π-conjugated systems of the pristine azaborole helicenes were enlarged with a phenanthrene unit leading to compounds with large Stokes shifts, significantly enhanced luminescence quantum yields (Φ) and dissymmetry factors (g\(_{lum}\)). The beneficial effect on optical properties was also observed for helical elongation. The combined contributions of lateral and helical extensions resulted in a compound showing green emission with Φ of 0.31 and |g\(_{lum}\)| of 2.2×10\(^{-3}\), highest within the series of π-extended azaborahelicenes and superior to emission intensity and chiroptical response of its non-extended congener. This study shows that helical and lateral extensions of π-conjugated systems are viable strategies to improve features of azaborole helicenes. In addition, single crystal X-ray analysis of configurationally stable [6]- and -[7]helicenes was used to provide insight into their packing arrangements.}, language = {en} } @article{KoleKošćakAmaretal.2022, author = {Kole, Goutam Kumar and Košćak, Marta and Amar, Anissa and Majhen, Dragomira and Božinović, Ksenija and Brkljaca, Zlatko and Ferger, Matthias and Michail, Evripidis and Lorenzen, Sabine and Friedrich, Alexandra and Krummenacher, Ivo and Moos, Michael and Braunschweig, Holger and Boucekkine, Abdou and Lambert, Christoph and Halet, Jean-Fran{\c{c}}ois and Piantanida, Ivo and M{\"u}ller-Buschbaum, Klaus and Marder, Todd B.}, title = {Methyl Viologens of Bis-(4'-Pyridylethynyl)Arenes - Structures, Photophysical and Electrochemical Studies, and their Potential Application in Biology}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {40}, doi = {10.1002/chem.202200753}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287126}, year = {2022}, abstract = {A series of bis-(4'-pyridylethynyl)arenes (arene=benzene, tetrafluorobenzene, and anthracene) were synthesized and their bis-N-methylpyridinium compounds were investigated as a class of π-extended methyl viologens. Their structures were determined by single crystal X-ray diffraction, and their photophysical and electrochemical properties (cyclic voltammetry), as well as their interactions with DNA/RNA were investigated. The dications showed bathochromic shifts in emission compared to the neutral compounds. The neutral compounds showed very small Stokes shifts, which are a little larger for the dications. All of the compounds showed very short fluorescence lifetimes (<4 ns). The neutral compound with an anthracene core has a quantum yield of almost unity. With stronger acceptors, the analogous bis-N-methylpyridinium compound showed a larger two-photon absorption cross-section than its neutral precursor. All of the dicationic compounds interact with DNA/RNA; while the compounds with benzene and tetrafluorobenzene cores bind in the grooves, the one with an anthracene core intercalates as a consequence of its large, condensed aromatic linker moiety, and it aggregates within the polynucleotide when in excess over DNA/RNA. Moreover, all cationic compounds showed highly specific CD spectra upon binding to ds-DNA/RNA, attributed to the rare case of forcing the planar, achiral molecule into a chiral rotamer, and negligible toxicity toward human cell lines at ≤10 μM concentrations. The anthracene-analogue exhibited intracellular accumulation within lysosomes, preventing its interaction with cellular DNA/RNA. However, cytotoxicity was evident at 1 μM concentration upon exposure to light, due to singlet oxygen generation within cells. These multi-faceted features, in combination with its two-photon absorption properties, suggest it to be a promising lead compound for development of novel light-activated theranostic agents.}, language = {en} } @article{BruecknerRitschelJimenez‐Hallaetal.2023, author = {Br{\"u}ckner, Tobias and Ritschel, Benedikt and Jim{\´e}nez-Halla, J. Oscar C. and Fantuzzi, Felipe and Duwe, Dario and Markl, Christian and Dewhurst, Rian D. and Dietz, Maximilian and Braunschweig, Holger}, title = {Metal-Free Intermolecular C-H Borylation of N-Heterocycles at B-B Multiple Bonds}, series = {Angewandte Chemie International Edition}, volume = {62}, journal = {Angewandte Chemie International Edition}, number = {5}, doi = {10.1002/anie.202213284}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312385}, year = {2023}, abstract = {Carbene-stabilized diborynes of the form LBBL (L=N-heterocyclic carbene (NHC) or cyclic alkyl(amino)carbene (CAAC)) induce rapid, high yielding, intermolecular ortho-C-H borylation at N-heterocycles at room temperature. A simple pyridyldiborene is formed when an NHC-stabilized diboryne is combined with pyridine, while a CAAC-stabilized diboryne leads to activation of two pyridine molecules to give a tricyclic alkylideneborane, which can be forced to undergo a further H-shift resulting in a zwitterionic, doubly benzo-fused 1,3,2,5-diazadiborinine by heating. Use of the extended N-heteroaromatic quinoline leads to a borylmethyleneborane under mild conditions via an unprecedented boron-carbon exchange process.}, language = {en} } @article{DietzArrowsmithReichletal.2022, author = {Dietz, Maximilian and Arrowsmith, Merle and Reichl, Stephan and Lugo-Fuentes, Leonardo I. and Jim{\´e}nez-Halla, J. Oscar C. and Scheer, Manfred and Braunschweig, Holger}, title = {Stable Two-Legged Parent Piano-Stool and Mixed Diborabenzene-E\(_{4}\) (E=P, As) Sandwich Complexes of Group 8}, series = {Angewandte Chemie International Edition}, volume = {61}, journal = {Angewandte Chemie International Edition}, number = {36}, doi = {10.1002/anie.202206840}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-293880}, year = {2022}, abstract = {A cyclic alkyl(amino)carbene-stabilized 1,4-diborabenzene (DBB) ligand enables the isolation of 18-electron two-legged parent piano-stool Fe\(^{0}\) and Ru\(^{0}\) complexes, [(η\(^{6}\)-DBB)M(CO)\(_{2}\)], the ruthenium complex being the first of its kind to be structurally characterized. [(η\(^{6}\)-DBB)Fe(CO)\(_{2}\)] reacts with E\(_{4}\) (E=P, As) to yield mixed DBB-cyclo-E\(_{4}\) sandwich complexes with planar E\(_{4}\)\(^{2-}\) ligands. Computational analyses confirm the strong electron-donating capacity of the DBB ligand and show that the E\(_{4}\) ligand is bound by four equivalent Fe-P σ bonds.}, language = {en} } @article{FergerRogerKoesteretal.2022, author = {Ferger, Matthias and Roger, Chantal and K{\"o}ster, Eva and Rauch, Florian and Lorenzen, Sabine and Krummenacher, Ivo and Friedrich, Alexandra and Košćak, Marta and Nestić, Davor and Braunschweig, Holger and Lambert, Christoph and Piantanida, Ivo and Marder, Todd B.}, title = {Electron-Rich EDOT Linkers in Tetracationic bis-Triarylborane Chromophores: Influence on Water Stability, Biomacromolecule Sensing, and Photoinduced Cytotoxicity}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {48}, doi = {10.1002/chem.202201130}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287241}, year = {2022}, abstract = {Three novel tetracationic bis-triarylboranes with 3,4-ethylenedioxythiophene (EDOT) linkers, and their neutral precursors, showed significant red-shifted absorption and emission compared to their thiophene-containing analogues, with one of the EDOT-derivatives emitting in the NIR region. Only the EDOT-linked trixylylborane tetracation was stable in aqueous solution, indicating that direct attachment of a thiophene or even 3-methylthiophene to the boron atom is insufficient to provide hydrolytic stability in aqueous solution. Further comparative analysis of the EDOT-linked trixylylborane tetracation and its bis-thiophene analogue revealed efficient photo-induced singlet oxygen production, with the consequent biological implications. Thus, both analogues bind strongly to ds-DNA and BSA, very efficiently enter living human cells, accumulate in several different cytoplasmic organelles with no toxic effect but, under intense visible light irradiation, they exhibit almost instantaneous and very strong cytotoxic effects, presumably attributed to singlet oxygen production. Thus, both compounds are intriguing theranostic agents, whose intracellular and probably intra-tissue location can be monitored by strong fluorescence, allowing switching on of the strong bioactivity by well-focused visible light.}, language = {en} } @article{RienschSwobodaLiketal.2021, author = {Riensch, Nicolas Alexander and Swoboda, Lukas and Lik, Artur and Krummenacher, Ivo and Braunschweig, Holger and Helten, Holger}, title = {Conjugated Bis(triarylboranes) with Disconnected Conjugation}, series = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie}, volume = {647}, journal = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie}, number = {5}, doi = {10.1002/zaac.202000476}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-258020}, pages = {421-424}, year = {2021}, abstract = {A series of methylene-bridged bis(triarylboranes) has been synthesized via two complementary routes using metal-free catalytic Si/B exchange condensation under mild conditions. The title compounds comprise two borane moieties that show effective internal π-conjugation involving the respective boron centers and the adjacent hetaryl groups. Conjugation between both borane units, however, is disrupted by the aliphatic linker. Cyclic voltammetry revealed minimal electronic communication between the boron centers, as evidenced by two closely spaced reduction processes. The UV-vis spectra showed bathochromic shifted absorption bands compared to related monoboranes, which is attributed to the methylene bridge. A further red-shift results upon introduction of methyl or SiMe\(_3\) groups at the terminal thiophene rings.}, language = {en} } @article{MatlerArrowsmithSchorretal.2021, author = {Matler, Alexander and Arrowsmith, Merle and Schorr, Fabian and Hermann, Alexander and Hofmann, Alexander and Lenczyk, Carsten and Braunschweig, Holger}, title = {Reactivity of Terminal Iron Borylenes and Bis(borylenes) with Carbodiimides: Cycloaddition, Metathesis, Insertion and C-H Activation Pathways}, series = {European Journal of Inorganic Chemistry}, volume = {2021}, journal = {European Journal of Inorganic Chemistry}, number = {45}, doi = {10.1002/ejic.202100629}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257397}, pages = {4619-4631}, year = {2021}, abstract = {The reactions of carbodiimides with the iron arylborylene complex [Fe=BDur(CO)\(_{3}\)(PMe\(_{3}\))] (Dur=2,3,5,6-Me\(_{4}\)C\(_{6}\)H) and the iron bis(borylene) complex [Fe{=BDur}{=BN(SiMe\(_{3}\))\(_{2}\)}(CO)\(_{3}\)] yield a wide variety of temperature-dependent products, including known FeBNC and novel FeBNB metallacycles, complexes of N-heterocyclic boracarbene and spiro-boracarbene ligands and a unique 1,3,2,4-diazadiborolyl pianostool complex, characterized by NMR spectroscopy and X-ray crystallography. The product distributions can be rationalized by considering sequences of cycloaddition, metathesis, insertion, and C-H activation pathways mainly governed by sterics.}, language = {en} } @article{GerlachMonningerSchleieretal.2021, author = {Gerlach, Marius and Monninger, Sophie and Schleier, Domenik and Hemberger, Patrick and Goettel, James T. and Braunschweig, Holger and Fischer, Ingo}, title = {Photoelectron Photoion Coincidence Spectroscopy of NCl\(_{3}\) and NCl\(_{2}\)}, series = {ChemPhysChem}, volume = {22}, journal = {ChemPhysChem}, number = {21}, doi = {10.1002/cphc.202100537}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257322}, pages = {2164-2167}, year = {2021}, abstract = {We investigate NCl\(_{3}\) and the NCl\(_{2}\) radical by photoelectron-photoion coincidence spectroscopy using synchrotron radiation. The mass selected threshold photoelectron spectrum (ms-TPES) of NCl\(_{3}\) is broad and unstructured due to the large geometry change. An ionization energy of 9.7±0.1 eV is estimated from the spectrum and supported by computations. NCl2 is generated by photolysis at 213 nm from NCl\(_{3}\) and its ms-TPES shows an extended vibrational progression with a 90 meV spacing that is assigned to the symmetric N-Cl stretching mode in the cation. An adiabatic ionization energy of 9.94 ± 0.02 eV is determined.}, language = {en} } @article{HuangHuKrummenacheretal.2022, author = {Huang, Mingming and Hu, Jiefeng and Krummenacher, Ivo and Friedrich, Alexandra and Braunschweig, Holger and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Base-Mediated Radical Borylation of Alkyl Sulfones}, series = {Chemistry—A European Journal}, volume = {28}, journal = {Chemistry—A European Journal}, number = {3}, doi = {10.1002/chem.202103866}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257281}, pages = {e202103866}, year = {2022}, abstract = {A practical and direct method was developed for the production of versatile alkyl boronate esters via transition metal-free borylation of primary and secondary alkyl sulfones. The key to the success of the strategy is the use of bis(neopentyl glycolato) diboron (B\(_{2}\)neop\(_{2}\)), with a stoichiometric amount of base as a promoter. The practicality and industrial potential of this protocol are highlighted by its wide functional group tolerance, the late-stage modification of complex compounds, no need for further transesterification, and operational simplicity. Radical clock, radical trap experiments, and EPR studies were conducted which show that the borylation process involves radical intermediates.}, language = {en} } @article{SchorrSchopperRienschetal.2021, author = {Schorr, Fabian and Schopper, Nils and Riensch, Nicolas and Fantuzzi, Felipe and Neder, Marco and Dewhurst, Rian D. and Thiess, Thorsten and Br{\"u}ckner, Tobias and Hammond, Kai and Helten, Holger and Finze, Maik and Braunschweig, Holger}, title = {Controlled Synthesis of Oligomers Containing Main-Chain B(sp\(^{2}\))-B(sp\(^{2}\)) Bonds}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {64}, doi = {10.1002/chem.202103366}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257274}, pages = {16043-16048}, year = {2021}, abstract = {A number of novel alkynyl-functionalized diarylbis(dimethylamino)diboranes(4) are prepared by salt metathesis, and the appended alkynyl groups are subjected to hydroboration. Their reactions with monohydroboranes lead to discrete boryl-appended diborane(4) species, while dihydroboranes induce their catenation to oligomeric species, the first known examples of well-characterized macromolecular species with B-B bonds. The oligomeric species were found to comprise up to ten repeat units and are soluble in common organic solvents. Some of the oligomeric species have good air stability and all were characterized by NMR and vibrational spectroscopy and size-exclusion chromatography techniques.}, language = {en} } @article{ArrowsmithEndresHeinzetal.2021, author = {Arrowsmith, Merle and Endres, Sara and Heinz, Myron and Nestler, Vincent and Holthausen, Max C. and Braunschweig, Holger}, title = {Probing the Boundaries between Lewis-Basic and Redox Behavior of a Parent Borylene}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {70}, doi = {10.1002/chem.202103256}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257154}, pages = {17660-17668}, year = {2021}, abstract = {The parent borylene (CAAC)(Me\(_{3}\)P)BH, 1 (CAAC=cyclic alkyl(amino)carbene), acts both as a Lewis base and one-electron reducing agent towards group 13 trichlorides (ECl\(_{3}\), E=B, Al, Ga, In), yielding the adducts 1-ECl\(_{3}\) and increasing proportions of the radical cation [1]\(^{•+}\) for the heavier group 13 analogues. With boron trihalides (BX\(_{3}\), X=F, Cl, Br, I) 1 undergoes sequential adduct formation and halide abstraction reactions to yield borylboronium cations and shows an increasing tendency towards redox processes for the heavier halides. Calculations confirm that 1 acts as a strong Lewis base towards EX3 and show a marked increase in the B-E bond dissociation energies down both group 13 and the halide group.}, language = {en} } @article{CuiDietzHaerterichetal.2021, author = {Cui, Jingjing and Dietz, Maximilian and H{\"a}rterich, Marcel and Fantuzzi, Felipe and Lu, Wei and Dewhurst, Rian D. and Braunschweig, Holger}, title = {Diphosphino-Functionalized 1,8-Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {63}, doi = {10.1002/chem.202102721}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256994}, pages = {15751-15756}, year = {2021}, abstract = {A 1,8-naphthyridine diphosphine (NDP) reacts with boron-containing Lewis acids to generate complexes featuring a number of different naphthyridine bonding modes. When exposed to diborane B\(_{2}\)Br\(_{4}\), NDP underwent self-deprotonation to afford [NDP-B\(_{2}\)Br\(_{3}\)]Br, an unsymmetrical diborane comprised of four fused rings. The reaction of two equivalents of monoborane BBr\(_{3}\) and NDP in a non-polar solvent provided the simple phosphine-borane adduct [NDP(BBr\(_{3}\))\(_{2}\)], which then underwent intramolecular halide abstraction to furnish the salt [NDP-BBr\(_{2}\)][BBr\(_{4}\)], featuring a different coordination mode from that of [NDP-B\(_{2}\)Br\(_{3}\)]Br. Direct deprotonation of NDP by KHMDS or PhCH2K generates mono- and dipotassium reagents, respectively. The monopotassium reagent reacts with one or half an equivalent of B\(_{2}\)(NMe\(_{2}\))\(_{2}\)Cl\(_{2}\) to afford NDP-based diboranes with three or four amino substituents.}, language = {en} } @article{BergerRueheSchwarzmannetal.2021, author = {Berger, Sarina M. and R{\"u}he, Jessica and Schwarzmann, Johannes and Phillipps, Alexandra and Richard, Ann-Katrin and Ferger, Matthias and Krummenacher, Ivo and Tumir, Lidija-Marija and Ban, Željka and Crnolatac, Ivo and Majhen, Dragomira and Barišić, Ivan and Piantanida, Ivo and Schleier, Domenik and Griesbeck, Stefanie and Friedrich, Alexandra and Braunschweig, Holger and Marder, Todd B.}, title = {Bithiophene-Cored, mono-, bis-, and tris-(Trimethylammonium)-Substituted, bis-Triarylborane Chromophores: Effect of the Number and Position of Charges on Cell Imaging and DNA/RNA Sensing}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {56}, doi = {10.1002/chem.202102308}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256963}, pages = {14057-14072}, year = {2021}, abstract = {The synthesis, photophysical, and electrochemical properties of selectively mono-, bis- and tris-dimethylamino- and trimethylammonium-substituted bis-triarylborane bithiophene chromophores are presented along with the water solubility and singlet oxygen sensitizing efficiency of the cationic compounds Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\). Comparison with the mono-triarylboranes reveals the large influence of the bridging unit on the properties of the bis-triarylboranes, especially those of the cationic compounds. Based on these preliminary investigations, the interactions of Cat\(^{1+}\), Cat\(^{2+}\), Cat(i)\(^{2+}\), and Cat\(^{3+}\) with DNA, RNA, and DNApore were investigated in buffered solutions. The same compounds were investigated for their ability to enter and localize within organelles of human lung carcinoma (A549) and normal lung (WI38) cells showing that not only the number of charges but also their distribution over the chromophore influences interactions and staining properties.}, language = {en} } @article{LindlGuoKrummenacheretal.2021, author = {Lindl, Felix and Guo, Xueying and Krummenacher, Ivo and Rauch, Florian and Rempel, Anna and Paprocki, Valerie and Dellermann, Theresa and Stennett, Tom E. and Lamprecht, Anna and Br{\"u}ckner, Tobias and Radacki, Krzysztof and B{\´e}langer-Chabot, Guillaume and Marder, Todd B. and Lin, Zhenyang and Braunschweig, Holger}, title = {Rethinking Borole Cycloaddition Reactivity}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {43}, doi = {10.1002/chem.202101290}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256888}, pages = {11226-11233}, year = {2021}, abstract = {Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels-Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long-established mechanistic picture of pericyclic rearrangements by demonstrating that seven-membered borepins (i. e., heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels-Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes.}, language = {en} } @article{GaertnerMarekArrowsmithetal.2021, author = {G{\"a}rtner, Annalena and Marek, Matth{\"a}us and Arrowsmith, Merle and Auerhammer, Dominic and Radacki, Krzysztof and Prieschl, Dominic and Dewhurst, Rian D. and Braunschweig, Holger}, title = {Boron- versus Nitrogen-Centered Nucleophilic Reactivity of (Cyano)hydroboryl Anions: Synthesis of Cyano(hydro)organoboranes and 2-Aza-1,4-diborabutatrienes}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {37}, doi = {10.1002/chem.202101025}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256853}, pages = {9694-9699}, year = {2021}, abstract = {Cyclic alkyl(amino)carbene-stabilized (cyano)hydroboryl anions were synthesized by deprotonation of (cyano)dihydroborane precursors. While they display boron-centered nucleophilic reactivity towards organohalides, generating fully unsymmetrically substituted cyano(hydro)organoboranes, they show cyano-nitrogen-centered nucleophilic reactivity towards haloboranes, resulting in the formation of hitherto unknown linear 2-aza-1,4-diborabutatrienes.}, language = {en} } @article{KrebsHaehnelKrummenacheretal.2021, author = {Krebs, Johannes and Haehnel, Martin and Krummenacher, Ivo and Friedrich, Alexandra and Braunschweig, Holger and Finze, Maik and Ji, Lei and Marder, Todd B.}, title = {Synthesis and Structure of an o-Carboranyl-Substituted Three-Coordinate Borane Radical Anion}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {31}, doi = {10.1002/chem.202100938}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256841}, pages = {8159-8167}, year = {2021}, abstract = {Bis(1-(4-tolyl)-carboran-2-yl)-(4-tolyl)-borane [(1-(4-MeC\(_{6}\)H\(_{4}\))-closo-1,2-C\(_{2}\)B\(_{10}\)H\(_{10}\)-2-)\(_{2}\)(4-MeC\(_{6}\)H\(_{4}\))B] (1), a new bis(o-carboranyl)-(R)-borane was synthesised by lithiation of the o-carboranyl precursor and subsequent salt metathesis reaction with (4-tolyl)BBr\(_{2}\). Cyclic voltammetry experiments on 1 show multiple distinct reduction events with a one-electron first reduction. In a selective reduction experiment the corresponding paramagnetic radical anion 1\(^{.-}\) was isolated and characterized. Single-crystal structure analyses allow an in-depth comparison of 1, 1\(^{.-}\), their calculated geometries, and the S\(_{1}\) excited state of 1. Photophysical studies of 1 show a charge transfer (CT) emission with low quantum yield in solution but a strong increase in the solid state. TD-DFT calculations were used to identify transition-relevant orbitals.}, language = {en} } @article{HessKrummenacherDellermannetal.2021, author = {Heß, Merlin and Krummenacher, Ivo and Dellermann, Theresa and Braunschweig, Holger}, title = {Rhodium-Mediated Stoichiometric Synthesis of Mono-, Bi-, and Bis-1,2-Azaborinines: 1-Rhoda-3,2-azaboroles as Reactive Precursors}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {37}, doi = {10.1002/chem.202100795}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256830}, pages = {9503-9507}, year = {2021}, abstract = {A series of highly substituted 1,2-azaborinines, including a phenylene-bridged bis-1,2-azaborinine, was synthesized from the reaction of 1,2-azaborete rhodium complexes with variously substituted alkynes. 1-Rhoda-3,2-azaborole complexes, which are accessible by phosphine addition to the corresponding 1,2-azaborete complexes, were also found to be suitable precursors for the synthesis of 1,2-azaborinines and readily reacted with alkynyl-substituted 1,2-azaborinines to generate new regioisomers of bi-1,2-azaborinines, which feature directly connected aromatic rings. Their molecular structures, which can be viewed as boron-nitrogen isosteres of biphenyls, show nearly perpendicular 1,2-azaborinine rings. The new method using rhodacycles instead of 1,2-azaborete complexes as precursors is shown to be more effective, allowing the synthesis of a wider range of 1,2-azaborinines.}, language = {en} } @article{KoleMerzAmaretal.2021, author = {Kole, Goutam Kumar and Merz, Julia and Amar, Anissa and Fontaine, Bruno and Boucekkine, Abdou and Nitsch, J{\"o}rn and Lorenzen, Sabine and Friedrich, Alexandra and Krummenacher, Ivo and Košćak, Marta and Braunschweig, Holger and Piantanida, Ivo and Halet, Jean-Fran{\c{c}}ois and M{\"u}ller-Buschbaum, Klaus and Marder, Todd B.}, title = {2- and 2,7-substituted para-N-methylpyridinium pyrenes: syntheses, molecular and electronic structures, photophysical, electrochemical, and spectroelectrochemical properties and binding to double-stranded (ds) DNA}, series = {Chemistry - A European Journal}, volume = {27}, journal = {Chemistry - A European Journal}, number = {8}, doi = {10.1002/chem.202004748}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256642}, pages = {2837-2853}, year = {2021}, abstract = {Two N-methylpyridinium compounds and analogous N-protonated salts of 2- and 2,7-substituted 4-pyridyl-pyrene compounds were synthesised and their crystal structures, photophysical properties both in solution and in the solid state, electrochemical and spectroelectrochemical properties were studied. Upon methylation or protonation, the emission maxima are significantly bathochromically shifted compared to the neutral compounds, although the absorption maxima remain almost unchanged. As a result, the cationic compounds show very large apparent Stokes shifts of up to 7200 cm\(^{-1}\). The N-methylpyridinium compounds have a single reduction at ca. -1.5 V vs. Fc/Fc\(^+\) in MeCN. While the reduction process was reversible for the 2,7-disubstituted compound, it was irreversible for the mono-substituted one. Experimental findings are complemented by DFT and TD-DFT calculations. Furthermore, the N-methylpyridinium compounds show strong interactions with calf thymus (ct)-DNA, presumably by intercalation, which paves the way for further applications of these multi-functional compounds as potential DNA-bioactive agents.}, language = {en} } @article{SchmidtFantuzziKlopfetal.2021, author = {Schmidt, Paul and Fantuzzi, Felipe and Klopf, Jonas and Schr{\"o}der, Niklas B. and Dewhurst, Rian D. and Braunschweig, Holger and Engel, Volker and Engels, Bernd}, title = {Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics}, series = {Chemistry - A European Journal}, volume = {27}, journal = {Chemistry - A European Journal}, number = {16}, doi = {10.1002/chem.202004619}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256636}, pages = {5160-5170}, year = {2021}, abstract = {Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.}, language = {en} } @article{LuJayaramanFantuzzietal.2022, author = {Lu, Wei and Jayaraman, Arumugam and Fantuzzi, Felipe and Dewhurst, Rian D. and H{\"a}rterich, Marcel and Dietz, Maximilian and Hagspiel, Stephan and Krummenbacher, Ivo and Hammond, Kai and Cui, Jingjing and Braunschweig, Holger}, title = {An unsymmetrical, cyclic diborene based on a chelating CAAC ligand and its small-molecule activation and rearrangement chemistry}, series = {Angewandte Chemie International Edition}, volume = {61}, journal = {Angewandte Chemie International Edition}, number = {3}, doi = {10.1002/anie.202113947}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256576}, year = {2022}, abstract = {A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved via consecutive two-electron reduction steps from an adduct of CAAC and B\(_2\)Br\(_4\)(SMe\(_2\))\(_2\). Theoretical studies revealed that this diborene has a considerably smaller HOMO-LUMO gap than those of reported NHC- and phosphine-supported diborenes. Complexation of the diborene with [AuCl(PCy\(_3\))] afforded two diborene-Au\(^I\) π complexes, while reaction with DurBH\(_2\), P\(_4\) and a terminal acetylene led to the cleavage of B-H, P-P, and C-C π bonds, respectively. Thermal rearrangement of the diborene gave an electron-rich cyclic alkylideneborane, which readily coordinated to Ag\(^I\) via its B=C double bond.}, language = {en} } @article{ZhangRadackiBraunschweigetal.2021, author = {Zhang, Fangyuan and Radacki, Krzysztof and Braunschweig, Holger and Lambert, Christoph and Ravat, Prince}, title = {Zinc-[7]helicenocyanine and its discrete π-stacked homochiral Dimer}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, doi = {10.1002/anie.202109380}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256534}, pages = {23656-23660}, year = {2021}, abstract = {In this communication, we demonstrate a novel approach to prepare a discrete dimer of chiral phthalocyanine (Pc) by exploiting the flexible molecular geometry of helicenes, which enables structural interlocking and strong aggregation tendency of Pcs. Synthesized [7]helicene-Pc hybrid molecular structure, zinc-[7]helicenocyanine (Zn-7HPc), exclusively forms a stable dimeric pair consisting of two homochiral molecules. The dimerization constants were estimated to be as high as 8.96×10\(^6\) M\(^{-1}\) and 3.42×107 M\(^{-1}\) in THF and DMSO, respectively, indicating remarkable stability of dimer. In addition, Zn\(^{-7}\)HPc exhibited chiral self-sorting behavior, which resulted in preferential formation of a homochiral dimer also in the racemic sample. Two phthalocyanine subunits in the dimeric form strongly communicate with each other as revealed by a large comproportionation constant and observation of an IV-CT band for the thermodynamically stable mixed-valence state.}, language = {en} } @article{BruecknerFantuzziStennettetal.2021, author = {Br{\"u}ckner, Tobias and Fantuzzi, Felipe and Stennett, Tom E. and Krummenacher, Ivo and Dewhurst, Rian D. and Engels, Bernd and Braunschweig, Holger}, title = {Isolation of neutral, mono-, and dicationic B\(_2\)P\(_2\) rings by diphosphorus addition to a boron-boron triple bond}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {24}, doi = {10.1002/anie.202102218}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256451}, pages = {13661-13665}, year = {2021}, abstract = {The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P-P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B-B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.}, language = {en} } @article{HagspielFantuzziDewhurstetal.2021, author = {Hagspiel, Stephan and Fantuzzi, Felipe and Dewhurst, Rian D. and G{\"a}rtner, Annalena and Lindl, Felix and Lamprecht, Anna and Braunschweig, Holger}, title = {Adducts of the parent boraphosphaketene H\(_2\)BPCO and their decarbonylative insertion chemistry}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {24}, doi = {10.1002/anie.202103521}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256470}, pages = {13666-13670}, year = {2021}, abstract = {The first examples of Lewis base adducts of the parent boraphosphaketene (H\(_2\)B-PCO) and their cyclodimers are prepared. One of these adducts is shown to undergo mild decarbonylation and phosphinidene insertion into a B-C bond of a borole, forming very rare examples of 1,2-phosphaborinines, B/P isosteres of benzene. The strong donor properties of these 1,2-phosphaborinines are confirmed by the synthesis of their π complexes with the Group 6 metals.}, language = {en} } @article{RamlerFantuzziGeistetal.2021, author = {Ramler, Jaqueline and Fantuzzi, Felipe and Geist, Felix and Hanft, Anna and Braunschweig, Holger and Engels, Bernd and Lichtenberg, Crispin}, title = {The dimethylbismuth cation: entry into dative Bi-Bi bonding and unconventional methyl exchange}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, doi = {10.1002/anie.202109545}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256543}, pages = {24388-24394}, year = {2021}, abstract = {The dimethyl bismuth cation, [BiMe\(_2\)(SbF\(_6\))], has been isolated and characterized. Reaction with BiMe\(_3\) allows access to the first compound featuring Bi→Bi donor-acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual S\(_E\)2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi-C bond cleavage.}, language = {en} } @article{CzernetzkiArrowsmithFantuzzietal.2021, author = {Czernetzki, Corinna and Arrowsmith, Merle and Fantuzzi, Felipe and G{\"a}rtner, Annalena and Tr{\"o}ster, Tobias and Krummenacher, Ivo and Schorr, Fabian and Braunschweig, Holger}, title = {A neutral beryllium(I) radical}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {38}, doi = {10.1002/anie.202108405}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256529}, pages = {20776-20780}, year = {2021}, abstract = {The reduction of a cyclic alkyl(amino)carbene (CAAC)-stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, UV/Vis spectroscopy and X-ray crystallography. DFT calculations show significant spin density at beryllium and confirm donor-acceptor bonding between an alkylberyllium radical fragment and a neutral CAAC ligand.}, language = {en} } @article{HeRauchFriedrichetal.2021, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Krebs, Johannes and Krummenacher, Ivo and Bertermann, R{\"u}diger and Nitsch, J{\"o}rn and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Phenylpyridyl-fused boroles: a unique coordination mode and weak B-N coordination-induced dual fluorescence}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {9}, doi = {10.1002/anie.202013692}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256423}, pages = {4833-4840}, year = {2021}, abstract = {Phenylpyridyl-fused boroles [TipPBB1]\(_4\) and TipPBB2 were synthesized and their properties investigated. [TipPBB1]\(_4\) forms a tetramer in both the solid state and solution. TipPBB2 contains a 4-coordinate boron atom in the solid state but dissociates to give a 3-coordinate boron species in solution. TipPBB2 shows interesting temperature-dependent dual fluorescence in solution because of the equilibrium between 3- and 4-coordinate boron species due to weak N⋅⋅⋅B intermolecular coordination.}, language = {en} } @article{HagspielArrowsmithFantuzzietal.2021, author = {Hagspiel, Stephan and Arrowsmith, Merle and Fantuzzi, Felipe and Vargas, Alfredo and Rempel, Anna and Hermann, Alexander and Br{\"u}ckner, Tobias and Braunschweig, Holger}, title = {Highly colored boron-doped thiazolothiazoles from the reductive dimerization of boron isothiocyanates}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {12}, doi = {10.1002/anie.202015508}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256432}, pages = {6446-6450}, year = {2021}, abstract = {Reduction of (CAAC)BBr\(_2\)(NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z-isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)-stabilized, boron-doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates.}, language = {en} } @article{HagspielFantuzziDewhurstetal.2021, author = {Hagspiel, Stephan and Fantuzzi, Felipe and Dewhurst, Rian D. and G{\"a}rtner, Annalena and Lindl, Felix and Lamprecht, Anna and Braunschweig, Holger}, title = {Addukte des Stammboraphosphaketens H\(_{2}\)BPCO und deren Insertionsreaktionen mittels Decarbonylierung}, series = {Angewandte Chemie}, volume = {133}, journal = {Angewandte Chemie}, number = {24}, doi = {10.1002/ange.202103521}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244803}, pages = {13780 -- 13784}, year = {2021}, abstract = {Die ersten Beispiele f{\"u}r Lewis-Basen-Addukte des Stammboraphosphaketens H\(_{2}\)B-PCO und ihre cyclischen Dimere wurden hergestellt. Eines dieser Addukte zeigt unter milden Bedingungen eine Decarbonylierung und anschließende Insertion des Phosphinidens in die B-C-Bindung eines Borols, was in der Bildung sehr seltener Beispiele f{\"u}r 1,2-Phosphaborinine, B,P-Isostere von Benzol, resultiert. Die starken Donoreigenschaften dieser 1,2-Phosphaborinine wurden durch die Synthese ihrer π-Komplexe mit Metallen der Gruppe 6 best{\"a}tigt.}, language = {de} } @article{BruneckerArrowsmithFantuzzietal.2021, author = {Brunecker, Carina and Arrowsmith, Merle and Fantuzzi, Felipe and Braunschweig, Holger}, title = {Platin-vermittelte Kupplung von B=N-Einheiten: Synthese von BNBN-Analoga von 1,3-Dienen und Butatrien}, series = {Angewandte Chemie}, volume = {133}, journal = {Angewandte Chemie}, number = {31}, doi = {10.1002/ange.202106161}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244792}, pages = {17000 -- 17004}, year = {2021}, abstract = {Die 1:2-Reaktion von [μ-(dmpm)Pt(nbe)]\(_{2}\) (dmpm=Bis(dimethylphosphino)methan, nbe=Norbornen) mit Cl\(_{2}\)BNR(SiMe\(_{3}\)) (R=tBu, SiMe\(_{3}\)) f{\"u}hrt durch eine B-N-Kupplung {\"u}ber eine ClSiMe\(_{3}\)-Eliminierung zu unsymmetrischen (N-Aminoboryl)aminoboryl-Pt\(^{I}\)\(_{2}\)-Komplexen. Eine anschließende intramolekulare ClSiMe\(_{3}\)-Eliminierung des tBu-Derivats f{\"u}hrt zu einer Cyclisierung der BNBN-Einheit unter Bildung eines einzigartigen 1,3,2,4-Diazadiboretidin-2-yl-Liganden. Im Gegensatz hierzu steht die analoge Reaktion mit Br\(_{2}\)BN(SiMe\(_{3}\))\(_{2}\), die {\"u}ber eine zweifache BrSiMe\(_{3}\)-Eliminierung zu einem Pt\(^{II}\)\(_{2}\)-A-Frame-Komplex f{\"u}hrt, der von einem linearen Isoster des Butatriens verbr{\"u}ckt wird. Strukturelle und theoretische Daten best{\"a}tigen eine π-Elektronen-Delokalisierung {\"u}ber die gesamte BNBN-Einheit.}, language = {de} } @article{CrumbachBachmannFritzeetal.2021, author = {Crumbach, Merian and Bachmann, Jonas and Fritze, Lars and Helbig, Andreas and Krummenacher, Ivo and Braunschweig, Holger and Helten, Holger}, title = {Dithiophene-Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {17}, doi = {10.1002/anie.202100295}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-238996}, pages = {9290 -- 9295}, year = {2021}, abstract = {Access to dithiophene-fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one-electron reduction processes. The weak aromatic character of the novel 1,2,7-azadiborepin ring is demonstrated with in-depth theoretical investigations using nucleus-independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.}, language = {en} } @article{RangFantuzziArrowsmithetal.2021, author = {Rang, Maximilian and Fantuzzi, Felipe and Arrowsmith, Merle and Krummenacher, Ivo and Beck, Eva and Witte, Robert and Matler, Alexander and Rempel, Anna and Bischof, Tobias and Radacki, Krzysztof and Engels, Bernd and Braunschweig, Holger}, title = {Reduktion und Umlagerung eines Bor(I)-Carbonylkomplexes}, series = {Angewandte Chemie}, volume = {133}, journal = {Angewandte Chemie}, number = {6}, doi = {10.1002/ange.202014167}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224409}, pages = {3000 -- 3005}, year = {2021}, abstract = {Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen-Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl-Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergest{\"u}tzte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar]\(^{.-}\) Zwischenstufe. Weiterf{\"u}hrende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.}, language = {de} } @article{RoyTroesterFantuzzietal.2021, author = {Roy, Dipak Kumar and Tr{\"o}ster, Tobias and Fantuzzi, Felipe and Dewhurst, Rian D. and Lenczyk, Carsten and Radacki, Krzysztof and Pranckevicius, Conor and Engels, Bernd and Braunschweig, Holger}, title = {Isolation and Reactivity of an Antiaromatic s-Block Metal Compound}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {7}, doi = {10.1002/anie.202014557}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224447}, pages = {3812 -- 3819}, year = {2021}, abstract = {The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry.}, language = {en} } @article{HuangWangDewhurstetal.2020, author = {Huang, Zhenguo and Wang, Suning and Dewhurst, Rian D. and Ignat'ev, Nikolai V. and Finze, Maik and Braunschweig, Holger}, title = {Boron: Its Role in Energy-Related Processes and Applications}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {23}, doi = {10.1002/anie.201911108}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218514}, pages = {8800 -- 8816}, year = {2020}, abstract = {Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy-efficient products has seen boron playing key roles in energy-related research, such as 1) activating and synthesizing energy-rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron-deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability—in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy-related processes and applications.}, language = {en} } @article{SaalfrankFantuzziKupferetal.2020, author = {Saalfrank, Christian and Fantuzzi, Felipe and Kupfer, Thomas and Ritschel, Benedikt and Hammond, Kai and Krummenacher, Ivo and Bertermann, R{\"u}diger and Wirthensohn, Raphael and Finze, Maik and Schmid, Paul and Engel, Volker and Engels, Bernd and Braunschweig, Holger}, title = {cAAC-stabilisierte 9,10-Diboraanthracene - offenschalige Singulettbiradikale}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {43}, doi = {10.1002/ange.202008206}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218582}, pages = {19502 -- 19507}, year = {2020}, abstract = {Geringe HOMO-LUMO-Abst{\"a}nde und eine hohe Ladungstr{\"a}germobilit{\"a}t pr{\"a}destinieren die h{\"o}heren Acene f{\"u}r Anwendungen im Bereich der Organoelektronik. Die Leistungsf{\"a}higkeit derartiger Verbindungen steigt hierbei dramatisch mit der Anzahl anellierter Benzolringe. Gr{\"o}ßere Acenmengen sind synthetisch bisher jedoch nur f{\"u}r Acene bis Heptacen verl{\"a}sslich zug{\"a}nglich. Theoretischen Studien zufolge besitzen (Oligo)acene offenschalige Singulettbiradikal- und (Poly)acene polyradikalische Grundzust{\"a}nde. Eindeutige experimentelle Belege f{\"u}r diese Vorhersagen sind hingegen {\"a}ußerst selten. Durch den Einbau von zwei Boratomen in das Anthracengrundger{\"u}st konnten wir den HOMO-LUMO-Abstand von Acenen dramatisch verringern und zwar ohne die Notwendigkeit einer Ausweitung des konjugierten π-Systems. Stabilisierung der Borzentren durch cyclische (Alkyl)(amino)carbene lieferte hierbei neutrale 9,10-Diboraanthracene mit disjunkten, offenschaligen Singulettbiradikal-Grundzust{\"a}nden.}, language = {en} } @article{PaprockiHrobarikHarrimanetal.2020, author = {Paprocki, Valerie and Hrob{\´a}rik, Peter and Harriman, Katie L. M. and Luff, Martin S. and Kupfer, Thomas and Kaupp, Martin and Murugesu, Muralee and Braunschweig, Holger}, title = {Ein neutrales 1,4-Diborabenzol als \(\pi\)-Ligand in Actinoidkomplexen}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {31}, doi = {10.1002/ange.202004501}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218181}, pages = {13209 -- 13216}, year = {2020}, abstract = {Die \(\pi\)-Koordination von Aren- und anionischen Heteroarenliganden ist ein allgegenw{\"a}rtiges Strukturmotiv in der metallorganischen Chemie der d- und f-Block-Elemente. Im Gegensatz dazu sind vergleichbare \(\pi\)-Wechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, f{\"u}r den f-Block weit weniger verbreitet, was z. T. mit einer geringeren Effektivit{\"a}t der Metall-zu-Ligand-R{\"u}ckbindung in Zusammenhang gebracht werden kann. F{\"u}r die Actinoide sind π-Komplexe mit neutralen Heteroarenliganden sogar g{\"a}nzlich unbekannt. Durch Ausnutzung der außergew{\"o}hnlichen \(\pi\)-Donorst{\"a}rke eines 1,4-Diborabenzols ist es uns nun gelungen, eine Reihe stabiler π-Halbsandwichkomplexe des Thoriums(IV) und des Urans(IV) {\"u}ber einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4-Diborabenzols mit ThCl\(_{4}\)(dme)\(_{2}\) bzw. UCl\(_{4}\) in Gegenwart einer Lewis-Base. Hierdurch konnten die ersten Beispiele f{\"u}r Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwich-artigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke Actinoid-Heteroaren-Wechselwirkung in diesen Molek{\"u}len im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der Ligand-zu-Metall-\(\pi\)-Wechselwirkung geleistet, w{\"a}hrend \(\pi\)/δ-R{\"u}ckbindungsanteile kaum eine Rolle spielen.}, language = {de} } @article{MerzDietrichNitschetal.2020, author = {Merz, Julia and Dietrich, Lena and Nitsch, J{\"o}rn and Krummenacher, Ivo and Braunschweig, Holger and Moos, Michael and Mims, David and Lambert, Christoph and Marder, Todd B.}, title = {Synthesis, Photophysical and Electronic Properties of Mono-, Di-, and Tri-Amino-Substituted Ortho-Perylenes, and Comparison to the Tetra-Substituted Derivative}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {52}, doi = {10.1002/chem.202001475}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217835}, pages = {12050 -- 12059}, year = {2020}, abstract = {We synthesized a series of new mono-, di-, tri- and tetra-substituted perylene derivatives with strong bis(para-methoxyphenyl)amine (DPA) donors at the uncommon 2,5,8,11-positions. The properties of our new donor-substituted perylenes were studied in detail to establish a structure-property relationship. Interesting trends and unusual properties are observed for this series of new perylene derivatives, such as a decreasing charge transfer (CT) character with increasing number of DPA moieties and individual reversible oxidations for each DPA moiety. Thus, (DPA)-Per possesses one reversible oxidation while (DPA)\(_{4}\)-Per has four. The mono- and di-substituted derivatives display unusually large Stokes shifts not previously reported for perylenes. Furthermore, transient absorption measurements of the new derivatives reveal an excited state with lifetimes of several hundred microseconds, which sensitizes singlet oxygen with quantum yields of up to 0.83.}, language = {en} } @article{SaalfrankFantuzziKupferetal.2020, author = {Saalfrank, Christian and Fantuzzi, Felipe and Kupfer, Thomas and Ritschel, Benedikt and Hammond, Kai and Krummenacher, Ivo and Bertermann, R{\"u}diger and Wirthensohn, Raphael and Finze, Maik and Schmid, Paul and Engel, Volker and Engels, Bernd and Braunschweig, Holger}, title = {cAAC-Stabilized 9,10-diboraanthracenes—Acenes with Open-Shell Singlet Biradical Ground States}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {43}, doi = {10.1002/anie.202008206}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217795}, pages = {19338 -- 19343}, year = {2020}, abstract = {Narrow HOMO-LUMO gaps and high charge-carrier mobilities make larger acenes potentially high-efficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have open-shell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMO-LUMO gap of acenes without the necessity of unfavorable elongation of their conjugated π system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10-diboraanthracenes, which are shown to feature disjointed, open-shell singlet biradical ground states.}, language = {en} } @article{NeesKupferHofmannetal.2020, author = {Nees, Samuel and Kupfer, Thomas and Hofmann, Alexander and Braunschweig, Holger}, title = {Planar Cyclopenten-4-yl Cations: Highly Delocalized π Aromatics Stabilized by Hyperconjugation}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {42}, doi = {10.1002/anie.202009644}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218358}, pages = {18809 -- 18815}, year = {2020}, abstract = {Theoretical studies predicted the planar cyclopenten-4-yl cation to be a classical carbocation, and the highest-energy isomer of C\(_{5}\)H\(_{7}\)\(^{+}\). Hence, its existence has not been verified experimentally so far. We were now able to isolate two stable derivatives of the cyclopenten-4-yl cation by reaction of bulky alanes Cp\(^{R}\)AlBr\(_{2}\) with AlBr3. Elucidation of their (electronic) structures by X-ray diffraction and quantum chemistry studies revealed planar geometries and strong hyperconjugation interactions primarily from the C-Al σ bonds to the empty p orbital of the cationic sp\(^{2}\) carbon center. A close inspection of the molecular orbitals (MOs) and of the anisotropy of current (induced) density (ACID), as well as the evaluation of various aromaticity descriptors indicated distinct aromaticity for these cyclopenten-4-yl derivatives, which strongly contrasts the classical description of this system. Here, strong delocalization of π electrons spanning the whole carbocycle has been verified, thus providing rare examples of π aromaticity involving saturated sp\(^{3}\) carbon atoms.}, language = {en} } @article{RauchFuchsFriedrichetal.2020, author = {Rauch, Florian and Fuchs, Sonja and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {Highly Stable, Readily Reducible, Fluorescent, Trifluoromethylated 9-Borafluorenes}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {56}, doi = {10.1002/chem.201905559}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218390}, pages = {12794 -- 12808}, year = {2020}, abstract = {Three different perfluoroalkylated borafluorenes (\(^{F}\)Bf) were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para substituents on their exo-aryl moieties, being a proton \(^{F}\)Xyl\(^{F}\)Bf, \(^{F}\)Xyl: 2,6-bis(trifluoromethyl)phenyl), a trifluoromethyl group (\(^{F}\)Mes\(^{F}\)Bf, \(^{F}\)Mes: 2,4,6-tris(trifluoromethyl)phenyl) or a dimethylamino group (p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf, p-NMe\(_{2}\)-\(^{F}\)Xyl: 4-(dimethylamino)-2,6-bis(trifluoromethyl)phenyl), respectively. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron-deficient derivative \(^{F}\)Mes\(^{F}\)Bf was also chemically reduced and its radical anion isolated and characterized. Furthermore, all compounds exhibit very long fluorescent lifetimes of about 250 ns up to 1.6 μs; however, the underlying mechanisms responsible for this differ. The donor-substituted derivative p-NMe\(_{2}\)-\(^{F}\)Xyl\(^{F}\)Bf exhibits thermally activated delayed fluorescence (TADF) from a charge-transfer (CT) state, whereas the \(^{F}\)Mes\(^{F}\)Bf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition-dipole moments.}, language = {en} } @article{RauchEndresFriedrichetal.2020, author = {Rauch, Florian and Endres, Peter and Friedrich, Alexandra and Sieh, Daniel and H{\"a}hnel, Martin and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Ji, Lei and Marder, Todd B.}, title = {An Iterative Divergent Approach to Conjugated Starburst Borane Dendrimers}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {57}, doi = {10.1002/chem.202001985}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218345}, pages = {12951 -- 12963}, year = {2020}, abstract = {Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C-H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF\(_{2}\)] or [N(nBu\(_{4}\))][HF\(_{2}\)]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas.}, language = {en} } @article{NeesKupferHofmannetal.2020, author = {Nees, Samuel and Kupfer, Thomas and Hofmann, Alexander and Braunschweig, Holger}, title = {Stabilisierung planarer Cyclopenten-4-yl-Kationen durch Hyperkonjugation und π-Delokalisierung}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {42}, doi = {10.1002/ange.202009644}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218456}, pages = {18971 -- 18978}, year = {2020}, abstract = {Theoretischen Untersuchungen zufolge stellt das planare Cyclopenten-4-yl-Kation das energetisch ung{\"u}nstigste C\(_{5}\)H\(_{7}\)\(^{+}\)-Isomer dar und ist am ehesten als klassisches Carbokation zu beschreiben, wobei dessen Existenz experimentell bislang noch nicht nachgewiesen werden konnte. Durch Umsetzung sterisch {\"u}berfrachteter Alane vom Typ Cp\(^{R}\)AlBr\(_{2}\) mit AlBr3 ist uns nun die Isolierung zweier stabiler Derivate des Cyclopenten-4-yl-Kations gelungen. Untersuchungen zu deren (elektronischer) Struktur (XRD, QM) offenbarten planare Geometrien und starke Hyperkonjugationswechselwirkungen zwischen den C-Al-σ-Bindungen und dem unbesetzten p-Orbital der kationischen sp\(^{2}\)-Kohlenstoffzentren. Die Analyse der Molek{\"u}lorbitale (MOs), der Anisotropie der induzierten Stromdichte (ACID) sowie verschiedener Aromatizit{\"a}tsdeskriptoren deuten hierbei auf ein hohes Maß an Delokalisierung und π-Aromatizit{\"a}t in diesen Systemen hin, was einer klassischen Beschreibung grundlegend widerspricht. Unsere Cyclopenten-4-yl-Kationen geh{\"o}ren somit zu den wenigen Beispielen aromatischer Carbocyclen, in denen eine Delokalisierung der π-Elektronen {\"u}ber ges{\"a}ttigte sp\(^{3}\)-Kohlenstoffatome hinweg beobachtet wird.}, language = {de} } @article{HermannFantuzziArrowsmithetal.2020, author = {Hermann, Alexander and Fantuzzi, Felipe and Arrowsmith, Merle and Zorn, Theresa and Krummenacher, Ivo and Ritschel, Benedikt and Radacki, Krzysztof and Engels, Bernd and Braunschweig, Holger}, title = {Oxidation, Coordination, and Nickel-Mediated Deconstruction of a Highly Electron-Rich Diboron Analogue of 1,3,5-Hexatriene}, series = {Angewandte Chemie, International Edition}, volume = {59}, journal = {Angewandte Chemie, International Edition}, number = {36}, doi = {10.1002/anie.202006131}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-240652}, pages = {15717-15725}, year = {2020}, abstract = {The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyl- diborene, which, although isoelectronic to a 1,3,5-triene, displays no extended p conjugation because of twisting of the C\(_2\)B\(_2\)C\(_2\) chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η\(^2\)-B\(_2\) and η\(^4\)-C\(_2\)B\(_2\) fashion, respectively, it undergoes a complex rearrangement to an η\(^4\)-1,3-diborete upon complexation with nickel(0).}, language = {en} } @article{BruecknerHessStennettetal.2021, author = {Br{\"u}ckner, Tobias and Heß, Merlin and Stennett, Tom E. and Rempel, Anna and Braunschweig, Holger}, title = {Synthesis of Boron Analogues of Enamines via Hydroamination of a Boron-Boron Triple Bond}, series = {Angewandte Chemie, International Edition}, volume = {60}, journal = {Angewandte Chemie, International Edition}, number = {2}, doi = {10.1002/anie.202012101}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-240669}, pages = {736-741}, year = {2021}, abstract = {An N-heterocyclic-carbene-stabilized diboryne undergoes rapid, high-yielding and catalyst-free hydroamina- tion reactions with primary amines, yielding 1-amino-2-hydro- diborenes, which can be considered boron analogues of enamines. The electronics of the organic substituent at nitrogen influence the structure and further reactivity of the diborene product. With electron-rich anilines, a second hydroamination can occur at the diborene to generate 1,1-diamino-2,2-dihy- drodiboranes. With isopropylamine, the electronic influence of the alkyl substituent upon the diborene leads to an unprece- dented boron-mediated intramolecular N-dearylation reaction of an N-heterocyclic carbene unit.}, language = {en} } @article{StennettJayaramanBrueckneretal.2020, author = {Stennett, Tom E. and Jayaraman, Arumugam and Br{\"u}ckner, Tobias and Schneider, Lea and Braunschweig, Holger}, title = {Hydrophosphination of boron-boron multiple bonds}, series = {Chemical Science}, volume = {11}, journal = {Chemical Science}, doi = {10.1039/c9sc05908c}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-240681}, pages = {1335-1341}, year = {2020}, abstract = {Five compounds containing boron-boron multiple bonds are shown to undergo hydrophosphination reactions with diphenylphosphine in the absence of a catalyst. With diborenes, the products obtained are highly dependent on the substitution pattern at the boron atoms, with both 1,1- and 1,2- hydrophosphinations observed. With a symmetrical diboryne, 1,2-hydrophosphination yields a hydro(phosphino)diborene. The different mechanistic pathways for the hydrophosphination of diborenes are rationalised with the aid of density functional theory calculations.}, language = {en} } @article{ThiessErnstKupferetal.2020, author = {Thiess, Torsten and Ernst, Moritz and Kupfer, Thomas and Braunschweig, Holger}, title = {Facile Access to Substituted 1,4-Diaza-2,3-Diborinines}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {13}, doi = {10.1002/chem.201905356}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214650}, pages = {2967 -- 2972}, year = {2020}, abstract = {Several bis(dimethylamino)-substituted 1,4-diaza-2,3-diborinines (DADBs) were synthesized with variable substituents at the backbone nitrogen atoms. By reaction with HCl or BX\(_{3}\) (X=Br, I), these species were successfully converted into their synthetically more useful halide congeners. The high versatility of the generated B-X bonds in further functionalization reactions at the boron centers was demonstrated by means of salt elimination (MeLi) and commutation (NMe\(_{2}\) DADBs) reactions, thus making the DADB system a general structural motif in diborane(4) chemistry. A total of 18 DADB derivatives were characterized in the solid state by X-ray diffraction, revealing a strong dependence of the heterocyclic bonding parameters from the exocyclic substitution pattern at boron. According to our experiments towards the realization of a Dipp-substituted, sterically encumbered DADB, the mechanism of DADB formation proceeds via a transient four-membered azadiboretidine intermediate that subsequently undergoes ring expansion to afford the six-membered DADB heterocycle.}, language = {en} } @article{EwingDellermannAngelWongetal.2020, author = {Ewing, William C. and Dellermann, Theresa and Angel Wong, Y. T. and Mattock, James D. and Vargas, Alfredo and Bryce, David L. and Dewhurst, Rian D. and Braunschweig, Holger}, title = {\(\pi\)-Complexes of Diborynes with Main Group Atoms}, series = {Chemistry - An Asian Journal}, volume = {15}, journal = {Chemistry - An Asian Journal}, number = {10}, doi = {10.1002/asia.202000185}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214677}, pages = {1553 -- 1557}, year = {2020}, abstract = {We present herein an in-depth study of complexes in which a molecule containing a boron-boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B-B triple bond and the tellurium center. These complexes thus extend the well-known Dewar-Chatt-Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of \(\pi\)-complexes in the \(\pi\)-complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal-free continuum with conventional unsaturated three-membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.}, language = {en} } @article{BruneckerMuessigArrowsmithetal.2020, author = {Brunecker, Carina and M{\"u}ssig, Jonas H. and Arrowsmith, Merle and Fantuzzi, Felipe and Stoy, Andreas and B{\"o}hnke, Julian and Hofmann, Alexander and Bertermann, R{\"u}diger and Engels, Bernd and Braunschweig, Holger}, title = {Boranediyl- and Diborane(4)-1,2-diyl-Bridged Platinum A-Frame Complexes}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {39}, doi = {10.1002/chem.202001168}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214707}, pages = {8518 -- 8523}, year = {2020}, abstract = {Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt\(^{0}\)\(_{2}\) complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt-B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt-B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.}, language = {en} } @article{BraunschweigKrummenacherMailaenderetal.2016, author = {Braunschweig, Holger and Krummenacher, Ivo and Mail{\"a}nder, Lisa and Pentecost, Leanne and Vargas, Alfredo}, title = {Formation of a stable radical by oxidation of a tetraorganoborate}, series = {Chemical Communications}, volume = {52}, journal = {Chemical Communications}, number = {43}, doi = {10.1039/c6cc02916g}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-191321}, pages = {7005-7008}, year = {2016}, abstract = {Herein, we describe the selective formation of a stable neutral spiroborate radical by one-electron oxidation of the corresponding tetraorganoborate salt Li[B(C\(_4\)Ph\(_4\))\(_2\)], formally containing a tetrahedral borate centre and a s-cis-butadiene radical cation as the spin-bearing site. Spectroscopic and computational methods have been used to determine the spin distribution and the chromism observed in the solid state.}, language = {en} } @article{BraunschweigEwingGhoshetal.2016, author = {Braunschweig, Holger and Ewing, William C. and Ghosh, Sundargopal and Kramer, Thomas and Mattock, James D. and {\"O}streicher, Sebastian and Vargas, Alfredo and Werner, Christine}, title = {Trimetallaborides as starting points for the syntheses of large metal-rich molecular borides and clusters}, series = {Chemical Science}, volume = {7}, journal = {Chemical Science}, number = {1}, doi = {10.1039/c5sc03206g}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-191511}, pages = {109-116}, year = {2016}, abstract = {Treatment of an anionic dimanganaborylene complex ([{Cp(CO)\(_2\)Mn}\(_2\)B]\(^-\)) with coinage metal cations stabilized by a very weakly coordinating Lewis base (SMe\(_2\)) led to the coordination of the incoming metal and subsequent displacement of dimethylsulfide in the formation of hexametalladiborides featuring planar four-membered M\(_2\)B\(_2\) cores (M = Cu, Au) comparable to transition metal clusters constructed around four-membered rings composed solely of coinage metals. The analogies between compounds consisting of B\(_2\)M\(_2\) units and M\(_4\) (M = Cu, Au) units speak to the often overlooked metalloid nature of boron. Treatment of one of these compounds (M = Cu) with a Lewis-basic metal fragment (Pt(PCy\(_3\))\(_2\)) led to the formation of a tetrametallaboride featuring two manganese, one copper and one platinum atom, all bound to boron in a geometry not yet seen for this kind of compound. Computational examination suggests that this geometry is the result of d\(^{10}\)-d\(^{10}\) dispersion interactions between the copper and platinum fragments.}, language = {en} } @unpublished{SchmidtFantuzziArrowsmithetal.2020, author = {Schmidt, Uwe and Fantuzzi, Felipe and Arrowsmith, Merle and Hermann, Alexander and Prieschl, Dominic and Rempel, Anna and Engels, Bernd and Braunschweig, Holger}, title = {Tuneable reduction of cymantrenylboranes to diborenes or borylene-derived boratafulvenes}, series = {Chemical Communications}, journal = {Chemical Communications}, doi = {10.1039/D0CC06398C}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-222149}, year = {2020}, abstract = {Whereas the reduction of N-heterocyclic carbene (NHC)-stabilised cymantrenyldibromoboranes, (NHC)BBr\(_2\)Cym, in benzene results in formation of the corresponding diborenes (NHC)\(_2\)B\(_2\)Cym\(_2\), a change of solvent to THF yields a borylene of the form (NHC)\(_2\)BCym, stabilised through its boratafulvene resonance form.}, language = {en} } @article{SchmidtWernerArrowsmithetal.2020, author = {Schmidt, Uwe and Werner, Luis and Arrowsmith, Merle and Deissenberger, Andrea and Hermann, Alexander and Hofmann, Alexander and Ullrich, Stefan and Mattock, James D. and Vargas, Alfredo and Braunschweig, Holger}, title = {Trans-selektive Dihydroborierung eines cis-Diborens durch Insertion: Synthese eines linearen sp\(^3\)-sp\(^2\)-sp\(^3\)-Triborans und anschließende Kationisierung}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {1}, doi = {10.1002/ange.201911645}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219713}, pages = {333-337}, year = {2020}, abstract = {Die Reaktion zwischen Aryl- und Amino(dihydro)boranen und Dibora[2]ferrocenophan 1 f{\"u}hrt zur Bildung von 1,3-trans-Dihydrotriboranen durch formale Hydrierung und Insertion eines Borylens in die B=B Doppelbindung. Die Aryltriboran-Derivate unterliegen einer reversiblen Photoisomerisierung zugunsten eines cis-1,2-μ-H-3-Hydrotriborans, w{\"a}hrend eine Hydridabstraktion zu kationischen Triboranen f{\"u}hrt, welche die ersten doppelt basenstabilisierten B\(_3\)H\(_4\)\(^+\)-Analoga darstellen.}, language = {de} } @article{Belanger‐ChabotBraunschweig2019, author = {B{\´e}langer-Chabot, Guillaume and Braunschweig, Holger}, title = {Hexahalodiborate Dianions: A New Family of Binary Boron Halides}, series = {Angewandte Chemie International Edition}, volume = {58}, journal = {Angewandte Chemie International Edition}, number = {40}, doi = {10.1002/anie.201906666}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219688}, pages = {14270-14274}, year = {2019}, abstract = {The electron-precise binary boron subhalide species [B\(_2\)X\(_6\)]\(^{2-}\) X=F, Br, I) were synthesized and their structures confirmed by X-ray crystallography. The existence of the previously claimed [B\(_2\)Cl\(_6\)]\(^{2-}\), which had been questioned, was also confirmed by X-ray crystallography. The dianions are isoelectronic to hexahaloethanes, are subhalide analogues of the well-known tetrahaloborate anions (BX\(_4\)\(^-\)), and are rare examples of molecular electron-precise binary boron species beyond B\(_2\)X\(_4\), BX\(_3\), and [BX\(_4\)]\(^-\).}, language = {en} } @article{BelangerChabotBraunschweig2019, author = {B{\´e}langer-Chabot, Guillaume and Braunschweig, Holger}, title = {Hexahalogendiborat-Dianionen: Eine neue Klasse bin{\"a}rer Borhalogenide}, series = {Angewandte Chemie}, volume = {131}, journal = {Angewandte Chemie}, number = {40}, doi = {10.1002/ange.201906666}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212605}, pages = {14408-14412}, year = {2019}, abstract = {Die elektronenpr{\"a}zisen bin{\"a}ren Borsubhalogenide [B\(_2\)X\(_6\)]\(^{2-}\) (X=F, Br, I) wurden synthetisiert und strukturell im Festk{\"o}rper untersucht. Zudem konnte die vermutete Existenz von [B\(_2\)Cl\(_6\)]\(^{2-}\) mittels R{\"o}ntgendiffraktometrie nachgewiesen werden. Diese Dianionen sind isoelektronisch zu den Hexahalogeniden des Ethans und k{\"o}nnen als Homologe des Tetrahalogenborat-Anions BX\(_4\)\(^-\) betrachtet werden. Dar{\"u}ber hinaus geh{\"o}ren sie zu den seltenen Beispielen von elektronenpr{\"a}zisen bin{\"a}ren Borverbindungen (B\(_2\)X\(_4\), BX\(_3\), [BX\(_4\)]\(^-\)).}, language = {de} } @article{MuessigLisinetskayaDewhurstetal.2020, author = {Muessig, Jonas H. and Lisinetskaya, Polina and Dewhurst, Rian D. and Bertermann, R{\"u}diger and Thaler, Melanie and Mitric, Roland and Braunschweig, Holger}, title = {Dibortetraiodid (B\(_2\)I\(_4\)) ist im Festk{\"o}rper ein Polymer aus sp3-hybridisiertem Bor}, series = {Angewandte Chemie}, volume = {132}, journal = {Angewandte Chemie}, number = {14}, doi = {10.1002/ange.201913590}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219653}, pages = {5574-5579}, year = {2020}, abstract = {Anhand der ersten Festk{\"o}rperstrukturen von Dibortetraiodid (B\(_2\)I\(_4\)) wird gezeigt, dass dieses nicht, wie lange angenommen, analog zu den leichteren Dibortetrahalogeniden B\(_2\)F\(_4\), B\(_2\)Cl\(_4\) und B\(_2\)Br\(_4\) in allen Aggregatzust{\"a}nden in Form diskreter Molek{\"u}le mit planaren, dreifach koordinierten Boratomen vorliegt. R{\"o}ntgenstrukturanalysen, Festk{\"o}rper-NMR- und IR-Messungen zeigen, dass B\(_2\)I\(_4\) im Festk{\"o}rper in zwei polymeren Konformeren vorkommt, die tetraedrisch koordinierte Boratome enthalten. Anhand von DFT-Rechnungen werden die IR-Spektren in L{\"o}sung und im Festk{\"o}rper simuliert und mit den experimentellen Daten verglichen.}, language = {de} } @article{LenczykRoyNitschetal.2019, author = {Lenczyk, Carsten and Roy, Dipak Kumar and Nitsch, J{\"o}rn and Radacki, Krzysztof and Rauch, Florian and Dewhurst, Rian D. and Bickelhaupt, F. Matthias and Marder, Todd B. and Braunschweig, Holger}, title = {Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {59}, issn = {1521-3765}, doi = {10.1002/chem.201902890}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-219537}, pages = {13566-13571}, year = {2019}, abstract = {The steric and electronic properties of aryl substituents in monoaryl borohydrides (Li[ArBH\(_3\)]) and dihydroboranes were systematically varied and their reactions with [Ru(PCy\(_3\))\(_2\)HCl(H\(_2\))] (Cy: cyclohexyl) were studied, resulting in bis(σ)-borane or terminal borylene complexes of ruthenium. These variations allowed for the investigation of the factors involved in the activation of dihydroboranes in the synthesis of terminal borylene complexes. The complexes were studied by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and density functional theory (DFT) calculations. The experimental and computational results suggest that the ortho-substitution of the aryl groups is necessary for the formation of terminal borylene complexes.}, language = {en} } @article{LiuLegareSeufertetal.2020, author = {Liu, Siyuan and L{\´e}gar{\´e}, Marc-Andr{\´e} and Seufert, Jens and Prieschl, Dominic and Rempel, Anna and Englert, Lukas and Dellermann, Theresa and Paprocki, Valerie and Stoy, Andreas and Braunschweig, Holger}, title = {2,2′-Bipyridyl as a Redox-Active Borylene Abstraction Agent}, series = {Inorganic Chemistry}, volume = {59}, journal = {Inorganic Chemistry}, number = {15}, doi = {10.1021/acs.inorgchem.0c01383}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-215595}, pages = {10866-10873}, year = {2020}, abstract = {2,2′-Bipyridyl is shown to spontaneously abstract a borylene fragment (R-B:) from various hypovalent boron compounds. This process is a redox reaction in which the bipyridine is reduced and becomes a dianionic substituent bound to boron through its two nitrogen atoms. Various transition metal-borylene complexes and diboranes, as a well as a diborene, take part in this reaction. In the latter case, our results show an intriguing example of the homolytic cleavage of a B═B double bond.}, language = {en} } @article{GoettelGaoDotzaueretal.2020, author = {Goettel, James T. and Gao, Haopeng and Dotzauer, Simon and Braunschweig, Holger}, title = {\(^{Me}\)CAAC=N\(^{-}\): A Cyclic (Alkyl)(Amino)Carbene Imino Ligand}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {5}, doi = {10.1002/chem.201904715}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212662}, pages = {1136-1143}, year = {2020}, abstract = {A cyclic (alkyl)(amino)carbene (CAAC) has been shown to react with a covalent azide similar to the Staudinger reaction. The reaction of \(^{Me}\)CAAC with trimethylsilyl azide afforded the N-silylated 2-iminopyrrolidine (\(^{Me}\)CAAC=NSiMe\(_{3}\)), which was fully characterized. This compound undergoes hydrolysis to afford the 2-iminopyrrolidine and trimethylsiloxane which co-crystallize as a hydrogen-bonded adduct. The N-silylated 2-iminopyrrolidine was used to transfer the novel pyrrolidine-2-iminato ligand onto both main-group and transition-metal centers. The reaction of the tetrabromodiborane bis(dimethyl sulfide) adduct with two equivalents of \(^{Me}\)CAAC=NSiMe\(_{3}\) afforded the disubstituted diborane. The reaction of \(^{Me}\)CAAC=NSiMe\(_{3}\) with TiCl\(_{4}\) and CpTiCl\(_{3}\) afforded \(^{Me}\)CAAC=NTiCl\(_{3}\) and \(^{Me}\)CAAC=NTiCl\(_{2}\)Cp, respectively.}, language = {en} } @article{LenczykRoyOberdorfetal.2019, author = {Lenczyk, Carsten and Roy, Dipak Kumar and Oberdorf, Kai and Nitsch, J{\"o}rn and Dewhurst, Rian D. and Radacki, Krzysztof and Halet, Jean-Fran{\c{c}}ois and Marder, Todd B. and Bickelhaupt, Matthias and Braunschweig, Holger}, title = {Toward Transition-Metal-Templated Construction of Arylated B\(_{4}\) Chains by Dihydroborane Dehydrocoupling}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {72}, doi = {10.1002/chem.201904772}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214324}, pages = {16544-16549}, year = {2019}, abstract = {The reactivity of a diruthenium tetrahydride complex towards three selected dihydroboranes was investigated. The use of [DurBH\(_{2}\)] (Dur=2,3,5,6-Me\(_{4}\)C\(_{6}\)H) and [(Me\(_{3}\)Si)\(_{2}\)NBH\(_{2}\)] led to the formation of bridging borylene complexes of the form [(Cp\(^{*}\)RuH)\(_{2}\)BR] (Cp\(^{*}\)=C\(_{5}\)Me\(_{5}\); 1 a: R=Dur; 1 b: R=N(SiMe\(_{3}\))\(_{2}\)) through oxidative addition of the B-H bonds with concomitant hydrogen liberation. Employing the more electron-deficient dihydroborane [3,5-(CF\(_{3}\))\(_{2}\)-C\(_{6}\)H\(_{3}\)BH\(_{2}\)] led to the formation of an anionic complex bearing a tetraarylated chain of four boron atoms, namely Li(THF)\(_{4}\)[(Cp\(^{*}\)Ru)\(_{2}\)B\(_{4}\)H\(_{5}\)(3,5-(CF\(_{3}\))\(_{2}\)C\(_{6}\)H\(_{3}\))\(_{4}\)] (4), through an unusual, incomplete threefold dehydrocoupling process. A comparative theoretical investigation of the bonding in a simplified model of 4 and the analogous complex nido-[1,2(Cp\(^{*}\)Ru)\(_{2}\)(μ-H)B\(_{4}\)H\(_{9}\)] (I) indicates that there appear to be no classical σ-bonds between the boron atoms in complex I, whereas in the case of 4 the B\(_{4}\) chain better resembles a network of three B-B σ bonds, the central bond being significantly weaker than the other two.}, language = {en} } @article{HattoriMichailSchmiedeletal.2019, author = {Hattori, Yohei and Michail, Evripidis and Schmiedel, Alexander and Moos, Michael and Holzapfel, Marco and Krummenacher, Ivo and Braunschweig, Holger and M{\"u}ller, Ulrich and Pflaum, Jens and Lambert, Christoph}, title = {Luminescent Mono-, Di-, and Tri-radicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {68}, doi = {10.1002/chem.201903007}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-208162}, pages = {15463-15471}, year = {2019}, abstract = {Up to three polychlorinated pyridyldiphenylmethyl radicals bridged by a triphenylamine carrying electron withdrawing (CN), neutral (Me), or donating (OMe) groups were synthesized and analogous radicals bridged by tris(2,6-dimethylphenyl)borane were prepared for comparison. All compounds were as stable as common closed-shell organic compounds and showed significant fluorescence upon excitation. Electronic, magnetic, absorption, and emission properties were examined in detail, and experimental results were interpreted using DFT calculations. Oxidation potentials, absorption and emission energies could be tuned depending on the electron density of the bridges. The triphenylamine bridges mediated intramolecular weak antiferromagnetic interactions between the radical spins, and the energy difference between the high spin and low spin states was determined by temperature dependent ESR spectroscopy and DFT calculations. The fluorescent properties of all radicals were examined in detail and revealed no difference for high and low spin states which facilitates application of these dyes in two-photon absorption spectroscopy and OLED devices.}, language = {en} } @article{MerzDietzVonhausenetal.2020, author = {Merz, Julia and Dietz, Maximilian and Vonhausen, Yvonne and W{\"o}ber, Frederik and Friedrich, Alexandra and Sieh, Daniel and Krummenacher, Ivo and Braunschweig, Holger and Moos, Michael and Holzapfel, Marco and Lambert, Christoph and Marder, Todd B.}, title = {Synthesis, Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor-Acceptor Pyrene Derivatives}, series = {Chemistry - A European Journal}, volume = {26}, journal = {Chemistry - A European Journal}, number = {2}, doi = {10.1002/chem.201904219}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-207486}, pages = {438-453}, year = {2020}, abstract = {We synthesized new pyrene derivatives with strong bis(para -methoxyphenyl)amine donors at the 2,7-positions and n -azaacene acceptors at the K-region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7-substituted pyrenes but not for K-region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin-Day class-II and delocalized Robin-Day class-III species.}, language = {en} } @article{HorrerKrahfussLubitzetal.2020, author = {Horrer, G{\"u}nther and Krahfuß, Mirjam J. and Lubitz, Katharina and Krummenacher, Ivo and Braunschweig, Holger and Radius, Udo}, title = {N-Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Complexes of Titanium(IV) and Titanium(III)}, series = {European Journal of Inorganic Chemistry}, volume = {2020}, journal = {European Journal of Inorganic Chemistry}, number = {3}, doi = {10.1002/ejic.201901207}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-208725}, pages = {281-291}, year = {2020}, abstract = {The reaction of one and two equivalents of the N -heterocyclic carbene IMes [IMes = 1,3-bis(2,4,6-trimethyl-phenyl)imidazolin-2-ylidene] or the cyclic (alkyl)(amino)carbene cAAC\(^{Me}\) [cAAC\(^{Me}\) = 1-(2,6-diisopropyl-phenyl)-3,3,5,5-tetra-methylpyrrolidin-2-ylidene] with [TiCl\(_{4}\)] in n -hexane results in the formation of mono- and bis-carbene complexes [TiCl\(_{4}\)(IMes)] 1 , [TiCl\(_{4}\)(IMes)2] 2 , [TiCl\(_{4}\)(cAAC\(^{Me}\))] 3 , and [TiCl\(_{4}\)(cAAC\(^{Me}\))\(_{2}\)] 4 , respectively. For comparison, the titanium(IV) NHC complex [TiCl\(_{4}\)(Ii Pr\(^{Me}\))] 5 (Ii Pr\(^{Me}\) = 1,3-diisopropyl-4,5-dimethyl-imidazolin-2-ylidene) has been synthesized and structurally characterized. The reaction of [TiCl\(_{4}\)(IMes)] 1 with PMe\(_{3}\) affords the mixed substituted complex [TiCl\(_{4}\)(IMes)(PMe\(_{3}\))] 6 . The reactions of [TiCl\(_{3}\)(THF)\(_{3}\)] with two equivalents of the carbenes IMes and cAAC\(^{Me}\) in n -hexane lead to the clean formation of the titanium(III) complexes [TiCl\(_{3}\)(IMes)\(_{2}\)] 7 and [TiCl\(_{3}\)(cAAC\(^{Me}\))\(_{2}\)] 8 . Compounds 1 -8 have been completely characterized by elemental analysis, IR and multinuclear NMR spectroscopy and for 2 -5 , 7 and 8 by X-ray diffraction. Magnetometry in solution, EPR and UV/Vis spectroscopy and DFT calculations performed on 7 and 8 are indicative of a predominantly metal-centered d\(^{1}\)-radical in both cases.}, language = {en} } @article{SchmidtWernerArrowsmithetal.2020, author = {Schmidt, Uwe and Werner, Luis and Arrowsmith, Merle and Deissenberger, Andrea and Hermann, Alexander and Hofmann, Alexander and Ullrich, Stefan and Mattock, James D. and Vargas, Alfredo and Braunschweig, Holger}, title = {trans-Selective Insertional Dihydroboration of a cis-Diborene: Synthesis of Linear sp\(^3\)-sp\(^2\)-sp\(^3\)-Triboranes and Subsequent Cationization}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {1}, doi = {10.1002/anie.201911645}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-208090}, pages = {325-329}, year = {2020}, abstract = {The reaction of aryl- and amino(dihydro)boranes with dibora[2]ferrocenophane 1 leads to the formation 1,3-trans -dihydrotriboranes by formal hydrogenation and insertion of a borylene unit into the B=B bond. The aryltriborane derivatives undergo reversible photoisomerization to the cis -1,2-μ-H-3-hydrotriboranes, while hydride abstraction affords cationic triboranes, which represent the first doubly base-stabilized B3H4\(^+\) analogues.}, language = {en} } @article{MuessigLisinetskayaDewhurstetal.2020, author = {Muessig, Jonas H. and Lisinetskaya, Polina and Dewhurst, Rian D. and Bertermann, R{\"u}diger and Thaler, Melanie and Mitric, Roland and Braunschweig, Holger}, title = {Tetraiododiborane(4) (B\(_2\)I\(_4\)) is a Polymer based on sp\(^3\) Boron in the Solid State}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, doi = {10.1002/anie.201913590}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-209428}, pages = {5531-5535}, year = {2020}, abstract = {Herein we present the first solid-state structures of tetraiododiborane(4) (B\(_2\)I\(_4\)), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B\(_2\)F\(_4\), B\(_2\)Cl\(_4\), and B\(_2\)Br\(_4\). Single-crystal X-ray diffraction, solid-state NMR, and IR measurements indicate that B\(_2\)I\(_4\) in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid-state structures, and these are compared with the experimental spectra.}, language = {en} } @article{ThiessMellerupBraunschweig2019, author = {Thiess, Torsten and Mellerup, Soren K. and Braunschweig, Holger}, title = {B-B Cleavage and Ring-Expansion of a 1,4,2,3-Diazadiborinine with N-Heterocyclic Carbenes}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {59}, doi = {10.1002/chem.201903259}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-206173}, pages = {13572-13578}, year = {2019}, abstract = {A 1,4,2,3-diazadiborinine derivative was found to form Lewis adducts with strong two-electron donors such as N-heterocyclic and cyclic (alkyl)(amino)carbenes. Depending on the donor, some of these Lewis pairs are thermally unstable, converting to sole B,N-embedded products upon gentle heating. The products of these reactions, which have been fully characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction, were identified as B,N-heterocycles with fused 1,5,2,4-diazadiborepine and 1,4,2-diazaborinine rings. Computational modelling of the reaction mechanism provides insight into the formation of these unique structures, suggesting that a series of B-H, C-N, and B-B bond activation steps are responsible for these "intercalation" reactions between the 1,4,2,3-diazadiborinine and NHCs.}, language = {en} } @article{HeRauchFriedrichetal.2019, author = {He, Jiang and Rauch, Florian and Friedrich, Alexandra and Sieh, Daniel and Ribbeck, Tatjana and Krummenacher, Ivo and Braunschweig, Holger and Finze, Maik and Marder, Todd B.}, title = {N-Heterocyclic Olefins as Electron Donors in Combination with Triarylborane Acceptors: Synthesis, Optical and Electronic Properties of D-π-A Compounds}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, doi = {10.1002/chem.201903118}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204690}, pages = {13777-13784}, year = {2019}, abstract = {N-heterocyclic olefins (NHOs), relatives of N-heterocyclic carbenes (NHCs), exhibit high nucleophilicity and soft Lewis basic character. To investigate their π-electron donating ability, NHOs were attached to triarylborane π-acceptors (A) giving donor (D)-π-A compounds 1-3. In addition, an enamine π-donor analogue (4) was synthesized for comparison. UV-visible absorption studies show a larger red shift for the NHO-containing boranes than for the enamine analogue, a relative of cyclic (alkyl)(amino) carbenes (CAACs). Solvent-dependent emission studies indicate that 1-4 have moderate intramolecular charge-transfer (ICT) behavior. Electrochemical investigations reveal that the NHO-containing boranes have extremely low reversible oxidation potentials (e.g., for 3, \(E^{ox}_{1/2}\) =-0.40 V vs. ferrocene/ferrocenium, Fc/Fc\(^+\), in THF). Time-dependent (TD) DFT calculations show that the HOMOs of 1-3 are much more destabilized than that of the enamine-containing 4, which confirms the stronger donating ability of NHOs.}, language = {en} } @article{AnsellKostakisBraunschweigetal.2016, author = {Ansell, Melvyn B. and Kostakis, George E. and Braunschweig, Holger and Navarro, Oscar and Spencer, John}, title = {Synthesis of functionalized hydrazines: facile homogeneous (N-heterocyclic carbene)-palladium(0)-catalyzed diboration and silaboration of azobenzenes}, series = {Advanced Synthesis \& Catalysis}, volume = {358}, journal = {Advanced Synthesis \& Catalysis}, number = {23}, doi = {10.1002/adsc.201601106}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186582}, pages = {3765-3769}, year = {2016}, abstract = {The bis(N-heterocyclic carbene)(diphenylacetylene)palladium complex Pd(ITMe)\(_2\)(PhCCPh)] (ITMe=1,3,4,5-tetramethylimidazol-2-ylidene) acts as a highly active pre-catalyst in the diboration and silaboration of azobenzenes to synthesize a series of novel functionalized hydrazines. The reactions proceed using commercially available diboranes and silaboranes under mild reaction conditions.}, language = {en} } @unpublished{HermannArrowsmithTrujilloGonzalezetal.2020, author = {Hermann, Alexander and Arrowsmith, Merle and Trujillo-Gonzalez, Daniel and Jim{\´e}nez-Halla, J. Oscar C. and Vargas, Alfredo and Braunschweig, Holger}, title = {Trapping of a Borirane Intermediate in the Reductive Coupling of an Arylborane to a Diborene}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.0c02306}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-203140}, year = {2020}, abstract = {The reductive coupling of an NHC-stabilized aryldibromoborane yields a mixture of trans- and cis-diborenes in which the aryl groups are coplanar with the diborene core. Under dilute reduction conditions two diastereomers of a borirane-borane intermediate are isolated, which upon further reduction give rise to the aforementioned diborene mixture. DFT calculations suggest a mechanism proceeding via nucleophilic attack of a dicoordinate borylene intermediate on the aryl ring and subsequent intramolecular B-B bond formation.}, language = {en} } @unpublished{BruecknerStennettHessetal.2019, author = {Br{\"u}ckner, Tobias and Stennett, Tom E. and Heß, Merlin and Braunschweig, Holger}, title = {Single and Double Hydroboration of B-B Triple Bonds and Conver- gent Routes to a Cationic Tetraborane}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.9b07991}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-188632}, year = {2019}, abstract = {A compound with a boron-boron triple bond is shown to undergo stepwise hydroboration reactions with catecholborane to yield an unsymmetrical hydro(boryl)diborene and a 2,3-dihydrotetraborane. Abstraction of H- from the latter compound produces an unusual cationic, planar tetraborane with a hydrogen atom bridging the central B2 moiety. Spectroscopic and crystallographic data and DFT calculations support a 'protonated diborene' structure for this compound, which can also be accessed via direct protonation of the corresponding diborene.}, language = {en} } @article{AuerhammerArrowsmithBraunschweigetal.2017, author = {Auerhammer, Dominic and Arrowsmith, Merle and Braunschweig, Holger and Dewhurst, Rian D. and Jim{\´e}nez-Halla, J. Oscar C. and Kupfer, Thomas}, title = {Nucleophilic addition and substitution at coordinatively saturated boron by facile 1,2-hydrogen shuttling onto a carbene donor}, series = {Chemical Science}, volume = {8}, journal = {Chemical Science}, number = {10}, doi = {10.1039/c7sc03193a}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170255}, pages = {7066-7071}, year = {2017}, abstract = {The reaction of [(cAAC\(^{Me}\))BH\(_{3}\)] (cAAC\(^{Me}\) = 1-(2,6-iPr\(_{2}\)C\(_{6}\)H\(_{3}\))-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li\(^{+}\)[(cAAC\(^{Me}\)H)BH\(_{2}\)R]- (R = sp\(^{3}\)-, sp\(^{2}\)-, or sp-hybridised organic substituent), by migration of one boron-bound hydrogen atom to the adjacent carbene carbon of the cAAC ligand. A subsequent deprotonation/salt metathesis reaction with Me3SiCl or spontaneous LiH elimination yielded the neutral cAAC-supported mono(organo)boranes, [(cAAC\(^{Me}\)H)BH\(_{2}\)R]- (R]. Similarly the reaction of [cAAC\(^{Me}\))BH\(_{3}\)] with a neutral donor base L resulted in adduct formation by shuttling one boron-bound hydrogen to the cAAC ligand, to generate [(cAAC\(^{Me}\)H)BH\(_{2}\)L], either irreversibly (L = cAAC\(^{Me}\)) or reversibly (L = pyridine). Variable-temperature NMR data and DFT calculations on [(cAAC\(^{Me}\)H)BH\(_{2}\)(cAAC\(^{Me}\))] show that the hydrogen on the former carbene carbon atom exchanges rapidly with the boron-bound hydrides.}, language = {en} } @article{BruecknerDewhurstDellermannetal.2019, author = {Br{\"u}ckner, Tobias and Dewhurst, Rian D. and Dellermann, Theresa and M{\"u}ller, Marcel and Braunschweig, Holger}, title = {Mild synthesis of diboryldiborenes by diboration of B-B triple bonds}, series = {Chemical Science}, volume = {10}, journal = {Chemical Science}, doi = {10.1039/C9SC02544H}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186306}, pages = {7375-7378}, year = {2019}, abstract = {A set of diboryldiborenes are prepared by the mild, catalyst-free, room-temperature diboration of the B-B triple bonds of doubly base-stabilized diborynes. Two of the product diboryldiborenes are found to be air- and water-stable in the solid state, an effect that is attributed to their high crystallinity and extreme insolubility in a wide range of solvents.}, language = {en} } @unpublished{LegarePranckeviciusBraunschweig2019, author = {L{\´e}gar{\´e}, Marc-Andr{\´e} and Pranckevicius, Conor and Braunschweig, Holger}, title = {Metallomimetic Chemistry of Boron}, series = {Chemical Reviews}, journal = {Chemical Reviews}, doi = {10.1021/acs.chemrev.8b00561}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186317}, year = {2019}, abstract = {The study of main-group molecules that behave and react similarly to transition-metal (TM) complexes has attracted significant interest in recent decades. Most notably, the attractive idea of replacing the all-too-often rare and costly metals from catalysis has motivated efforts to develop main-group-element-mediated reactions. Main-group elements, however, lack the electronic flexibility of TM complexes that arises from combinations of empty and filled d orbitals and that seem ideally suited to bind and activate many substrates. In this review, we look at boron, an element that despite its nonmetal nature, low atomic weight, and relative redox staticity has achieved great milestones in terms of TM-like reactivity. We show how in interelement cooperative systems, diboron molecules, and hypovalent complexes the fifth element can acquire a truly metallomimetic character. As we discuss, this character is powerfully demonstrated by the reactivity of boron-based molecules with H2, CO, alkynes, alkenes and even with N2.}, language = {en} } @unpublished{EnglertStoyArrowsmithetal.2019, author = {Englert, Lukas and Stoy, Andreas and Arrowsmith, Merle and M{\"u}ssig, Jonas H. and Thaler, Melanie and Deißenberger, Andrea and H{\"a}fner, Alena and B{\"o}hnke, Julian and Hupp, Florian and Seufert, Jens and Mies, Jan and Damme, Alexander and Dellermann, Theresa and Hammond, Kai and Kupfer, Thomas and Radacki, Krzysztof and Thiess, Torsten and Braunschweig, Holger}, title = {Stable Lewis Base Adducts of Tetrahalodiboranes: Synthetic Methods and Structural Diversity}, series = {Chemistry - A European Journal}, journal = {Chemistry - A European Journal}, doi = {10.1002/chem.201901437}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-184888}, year = {2019}, abstract = {A series of 22 new bis(phosphine), bis(carbene) and bis(isonitrile) tetrahalodiborane adducts has been synthesized, either by direct adduct formation with highly sensitive B2X4 precursors (X = Cl, Br, I) or by ligand exchange at stable B2X4(SMe2)2 precursors (X = Cl, Br) with labile dimethylsulfide ligands. The isolated compounds have been fully characterized using NMR spectroscopic, (C,H,N)- elemental and, for 20 of these compounds, X-ray crystallographic analysis, revealing an unexpected variation in the bonding motifs. Besides the classical B2X4L2 diborane(6) adducts, some of the more sterically demanding carbene ligands induce a halide displacement leading to the first halide-bridged monocationic diboron species, [B2X3L2]A (A = BCl4, Br, I). Furthermore, low-temperature 1:1 reactions of B2Cl4 with sterically demanding N-heterocyclic carbenes led to the formation of kinetically unstable mono-adducts, one of which was structurally characterized. A comparison of the NMR and structural data of new and literature-known bis-adducts shows several trends pertaining to the nature of the halides and the stereoelectronic properties of the Lewis bases employed.}, language = {en} } @unpublished{BruecknerArrowsmithHessetal.2019, author = {Br{\"u}ckner, Tobias and Arrowsmith, Merle and Heß, Merlin and Hammond, Kai and M{\"u}ller, Marcel and Braunschweig, Holger}, title = {Synthesis of fused B,N-heterocycles by alkyne cleavage, NHC ring-expansion and C-H activation at a diboryne}, series = {Chemical Communications}, journal = {Chemical Communications}, doi = {10.1039/C9CC02657F}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-184899}, year = {2019}, abstract = {The addition of alkynes to a staturated N-heterocyclic carbene (NHC)-supported diboryne results in spontaneous cycloaddition, with complete B≡B and C≡C triple bond cleavage, NHC ring- expansion and activation of a variety of C-H bonds, leading to the formation of complex mixtures of fused B,N-heterocycles.}, language = {en} } @unpublished{ArrowsmithDoemlingSchmidtetal.2019, author = {Arrowsmith, Merle and D{\"o}mling, Michael and Schmidt, Uwe and Werner, Luis and Castro, Abril C. and Jim{\´e}nez-Halla, J. Oscar C. and M{\"u}ssig, Jonas and Prieschl, Dominic and Braunschweig, Holger}, title = {Spontaneous trans-Selective Transfer Hydrogenation of Apolar B=B Double Bonds}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201902656}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-184874}, year = {2019}, abstract = {The transfer hydrogenation of NHC-supported diborenes with dimethylamine borane proceeds with high selectivity for the trans-1,2-dihydrodiboranes(6). DFT calculations suggest a stepwise proton-first-hydride-second reaction mechanism via an intermediate μ-hydrodiboronium dimethylaminoborate ion pair.}, language = {en} } @unpublished{StennettBissingerGriesbecketal.2019, author = {Stennett, Tom E. and Bissinger, Philipp and Griesbeck, Stefanie and Ullrich, Stefan and Krummenacher, Ivo and Auth, Michael and Sperlich, Andreas and Stolte, Matthias and Radacki, Krzysztof and Yao, Chang-Jiang and W{\"u}rthner, Frank and Steffen, Andreas and Marder, Todd B. and Braunschweig, Holger}, title = {Near-Infrared Quadrupolar Chromophores Combining Three-Coordinate Boron-Based Superdonor and Superacceptor Units}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201900889}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-180391}, year = {2019}, abstract = {In this work, two new quadrupolar A-π-D-π-A chromophores have been prepared featuring a strongly electron- donating diborene core and strongly electron-accepting dimesitylboryl F(BMes2) and bis(2,4,6-tris(trifluoromethyl)phenyl)boryl (BMes2) end groups. Analysis of the compounds by NMR spectroscopy, X-ray crystallography, cyclic voltammetry and UV-vis-NIR absorption and emission spectroscopy indicated that the compounds possess extended conjugated π-systems spanning their B4C8 cores. The combination of exceptionally potent π-donor (diborene) and π- acceptor (diarylboryl) groups, both based on trigonal boron, leads to very small HOMO-LUMO gaps, resulting in strong absorption in the near-IR region with maxima in THF at 840 and 1092 nm, respectively, and very high extinction coefficients of ca. 120,000 M-1cm-1. Both molecules also display weak near-IR fluorescence with small Stokes shifts.}, language = {en} } @unpublished{MuessigThalerDewhurstetal.2019, author = {Muessig, Jonas H. and Thaler, Melanie and Dewhurst, Rian D. and Paprocki, Valerie and Seufert, Jens and Mattock, James D. and Vargas, Alfredo and Braunschweig, Holger}, title = {Phosphine-Stabilized Diiododiborenes: Isolable Diborenes with Six Labile Bonds}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201814230}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178608}, year = {2019}, abstract = {The lability of B=B, B-P and B-halide bonds is combined in the syntheses of the first diiododiborenes. In a series of reactivity tests, these diiododiborenes demonstrate cleavage of all six of their central bonds in different ways, leading to products of B=B hydrogenation and dihalogenation as well as halide exchange.}, language = {en} } @article{ArnoldBraunschweigGruss2011, author = {Arnold, Thomas and Braunschweig, Holger and Gruss, Katrin}, title = {cyclo-Tri-mu-oxido-tris{[(eta 5,eta 5)-1,2-bis(cyclopentadienyl)-1,1,2,2-tetramethyldisilane]zirconium(IV)}: a trimeric disila-bridged oxidozirconocene}, series = {Acta Crystallographica Section E: metal-organic compounds}, volume = {67}, journal = {Acta Crystallographica Section E: metal-organic compounds}, doi = {10.1107/S1600536811007094}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-134802}, pages = {M391-sup-23}, year = {2011}, abstract = {The title compound, [Zr(3)(C(14)H(20)Si(2))(3)O(3)], consists of three disila-bridged zirconocene units, which are connected via an oxide ligand, forming a nearly planar six-membered ring with a maximum displacement of 0.0191 (8) A. The compound was isolated as a by-product from a mixture of [(C(5)H(4)SiMe(2))(2)ZrCl(2)] and Li[AlH(4)] in Et(2)O.}, language = {en} } @unpublished{StennettMattockPentecostetal.2018, author = {Stennett, Tom and Mattock, James and Pentecost, Leanne and Vargas, Alfredo and Braunschweig, Holger}, title = {Chelated Diborenes and their Inverse-Electron-Demand Diels- Alder Reactions with Dienes}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201809217}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178268}, year = {2018}, abstract = {A doubly base-stabilized diborane based on a benzylphosphine linker was prepared by a salt elimination reaction between 2-LiC\(_6\)H\(_4\)CH\(_2\)PCy\(_2\).Et\(_2\)O and B\(_2\)Br\(_4\). This compound was reduced with KC8 to its corresponding diborene, with the benzylphosphine forming a five-membered chelate. The diborene reacts with butadiene, 2-trimethylsiloxy-1,3-butadiene and isoprene to form 4,5-diboracyclohexenes, which interconvert between their 1,1- (geminal) and 1,2- (vicinal) chelated isomers. The 1,1-chelated diborene undergoes a halide-catalysed isomerisation into its thermodynamically favoured 1,2-isomer, which undergoes Diels-Alder reactions more slowly than the kinetic product.}, language = {en} } @unpublished{StennettBertermannBraunschweig2018, author = {Stennett, Tom and Bertermann, R{\"u}diger and Braunschweig, Holger}, title = {Construction of Linear and Branched Tetraboranes via 1,1- and 1,2-Diboration of Diborenes}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201809976}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178276}, year = {2018}, abstract = {Sterically unencumbered diborenes based on a benzylphosphine chelate undergo diboration reactions with bis(catecholato)diboron in the absence of a catalyst to yield tetraboranes. The symmetrical diborenes studied undergo 1,2- diborations, whereas an unsymmetrical derivative was found to yield a triborylborane-phosphine adduct as the result of a formal 1,1-diboration. A related borylborylene compound also underwent a 1,2-diboration to produce a borylene-borane adduct.}, language = {en} } @unpublished{BoehnkeArrowsmithBraunschweig2018, author = {B{\"o}hnke, Julian and Arrowsmith, Merle and Braunschweig, Holger}, title = {Activation of a Zerovalent Diboron Compound by Desymmetrization}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.8b06930}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167983}, year = {2018}, abstract = {The desymmetrization of the cyclic (alkyl)(amino)carbene-supported diboracumulene, B\(_2\)(cAAC\(^{Me}\))\(_2\) (cAAC\(^{Me}\) = 1- (2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) by mono-adduct formation with IMe\(^{Me}\) (1,3-dimethylimidazol-2-ylidene) yields the zerovalent sp-sp\(^2\) diboron compound B\(_2\)(cAAC\(^{Me}\))\(_2\)(IMe\(^{Me}\)), which provides a versatile platform for the synthesis of novel symmetrical and unsymmetrical zerovalent sp\(^2\)-sp\(^2\) diboron compounds by adduct formation with IMe\(^{Me}\) and CO, respectively. Furthermore, B\(_2\)(cAAC\(^{Me}\))\(_2\)(IMe\(^{Me}\)) displays enhanced reactivity compared to its symmetrical precursor, undergoing spontaneous intramolecular C-H activation and facile twofold hydrogenation, the latter resulting in B-B bond cleavage and the formation of the mixed-base parent borylene, (cAAC\(^{Me}\))(IMe\(^{Me}\))BH.}, language = {en} } @unpublished{HermannCidMattocketal.2018, author = {Hermann, Alexander and Cid, Jessica and Mattock, James D. and Dewhurst, Rian D. and Krummenacher, Ivo and Vargas, Alfredo and Ingleson, Michael J. and Braunschweig, Holger}, title = {Diboryldiborenes: π-Conjugated B\(_4\) Chains Isoelectronic to the Butadiene Dication}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201805394}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167977}, year = {2018}, abstract = {sp\(^2\)-sp\(^3\) diborane species based on bis(catecholato)diboron and N-heterocyclic carbenes (NHCs) are subjected to catechol/bromide exchange selectively at the sp\(^3\) boron atom. The reduction of the resulting 1,1-dibromodiborane adducts led to reductive coupling and isolation of doubly NHC-stabilized 1,2-diboryldiborenes. These compounds are the first examples of molecules exhibiting pelectron delocalization over an all-boron chain.}, language = {en} } @article{BoehnkeBruecknerHermannetal.2018, author = {B{\"o}hnke, Julian and Br{\"u}ckner, Tobias and Hermann, Alexander and Gonz{\´a}lez-Belman, Oscar F. and Arrowsmith, Merle and Jim{\´e}nez-Halla, J. Oscar C. and Braunschweig, Holger}, title = {Single and double activation of acetone by isolobal B≡N and B≡B triple bonds}, series = {Chemical Science}, volume = {9}, journal = {Chemical Science}, doi = {10.1039/c8sc01249k}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164286}, pages = {5354-5359}, year = {2018}, abstract = {B≡N and B≡B triple bonds induce C-H activation of acetone to yield a (2-propenyloxy)aminoborane and an unsymmetrical 1-(2- propenyloxy)-2-hydrodiborene, respectively. DFT calculations showed that, despite their stark electronic differences, both the B≡N and B≡B triple bonds activate acetone via a similar coordination-deprotonation mechansim. In contrast, the reaction of acetone with a cAAC-supported diboracumulene yielded a unique 1,2,3-oxadiborole, which according to DFT calculations also proceeds via an unsymmetrical diborene, followed by intramolecular hydride migration and a second C-H activation of the enolate ligand.}, language = {en} } @unpublished{StoyBoehnkeJiménezHallaetal.2018, author = {Stoy, Andreas and B{\"o}hnke, Julian and Jiménez-Halla, J. Oscar C. and Dewhurst, Rian D. and Thiess, Torsten and Braunschweig, Holger}, title = {CO\(_2\) Binding and Splitting by Boron-Boron Multiple Bonds}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201802117}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164265}, year = {2018}, abstract = {CO\(_2\) is found to undergo room-temperature, ambient- pressure reactions with two species containing boron-boron multiple bonds, leading to incorporation of either one or two CO\(_2\) molecules. In one case, a thermally-unstable intermediate was structurally characterized, indicating the operation of an initial 2+2 cycloaddition mechanism in the reaction.}, language = {en} } @unpublished{CidHermannRadcliffeetal.2018, author = {Cid, Jessica and Hermann, Alexander and Radcliffe, James E. and Curless, Liam D. and Braunschweig, Holger and Ingleson, Michael J.}, title = {Synthesis of Unsymmetrical Diboron(5) Compounds and Their Conversion to Diboron(5) Cations}, series = {Organometallics}, journal = {Organometallics}, doi = {10.1021/acs.organomet.8b00288}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164299}, year = {2018}, abstract = {Reaction of bis-catecholatodiboron-NHC adducts, B\(_2\)Cat\(_2\)(NHC), (NHC = IMe (tetramethylimidazol-2-ylidene), IMes (1,3-dimesitylimidazol-2-ylidene) or IDIPP (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)) with BCl3 results in the replacement of the catecholato group bound to the four coordinate boron with two chlorides to yield diboron(5) Lewis acid-base adducts of formula CatB-BCl\(_2\)(NHC). These compounds are precursors to diboron(5) monocations, accessed by adding AlCl\(_3\) or K[B(C\(_6\)F\(_5\))\(_4\)] as halide abstraction agents in the presence of a Lewis base. The substitution of the chlorides of CatB-BCl\(_2\)(NHC) for hydrides is achieved using Bu\(_3\)SnH and a halide abstracting agent to form 1,1-dihydrodiboron(5) compounds, CatB-BH\(_2\)(NHC). Attempts to generate diboron(4) monocations of formula [CatB-B(Y)(NHC)]\(^+\) (Y = Cl or H) led to the rapid formation of CatBY.}, language = {en} } @unpublished{ArrowsmithMattockBoehnkeetal.2018, author = {Arrowsmith, Merle and Mattock, James D. and B{\"o}hnke, Julian and Krummenacher, Ivo and Vargas, Alfredo and Braunschweig, Holger}, title = {Direct access to a cAAC-supported dihydrodiborene and its dianion}, series = {Chemical Communications}, journal = {Chemical Communications}, doi = {10.1039/C8CC01580E}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164276}, year = {2018}, abstract = {The two-fold reduction of (cAAC)BHX\(_2\) (cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene; X = Cl, Br) provides a facile, high-yielding route to the dihydrodiborene (cAAC)\(_2\)B\(_2\)H\(_2\). The (chloro)hydroboryl anion reduction intermediate was successfully isolated using a crown ether. Overreduction of the diborene to its dianion [(cAAC)\(_2\)B\(_2\)H\(_2\)]\(^{2-}\) causes a decrease in the B-B bond order whereas the B-C bond orders increase.}, language = {en} } @article{BoehnkeDellermannCeliketal.2018, author = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger}, title = {Isolation of diborenes and their 90°-twisted diradical congeners}, series = {Nature Communications}, volume = {9}, journal = {Nature Communications}, number = {Article number: 1197}, doi = {10.1038/s41467-018-02998-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160431}, year = {2018}, abstract = {Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.}, language = {en} } @unpublished{BoehnkeDellermannCeliketal.2018, author = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger}, title = {Isolation of diradical products of twisted double bonds}, series = {Nature Communications}, journal = {Nature Communications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160248}, year = {2018}, abstract = {Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.}, language = {en} } @unpublished{StennettMattockVollertetal.2018, author = {Stennett, Tom and Mattock, James and Vollert, Ivonne and Vargas, Alfredo and Braunschweig, Holger}, title = {Unsymmetrical, Cyclic Diborenes and Thermal Rearrangement to a Borylborylene}, series = {Angewandte Chemie, International Edition}, volume = {57}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201800671}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160258}, pages = {4098-4102}, year = {2018}, abstract = {Cyclic diboranes(4) based on a chelating monoanionic, benzylphosphine linker were prepared by boron-silicon exchange between arylsilanes and B\(_2\)Br\(_4\). Coordination of Lewis bases to the remaining sp\(^2\) boron atom yielded unsymmetrical sp\(^3\)-sp\(^3\) diboranes, which were reduced with KC\(_8\) to their corresponding trans-diborenes. These compounds were studied by a combination of spectroscopic methods, X-ray diffraction and DFT calculations. PMe\(_3\)-stabilized diborene 6 was found to undergo thermal rearrangement to gem- diborene 8. DFT calculations on 8 reveal a polar boron-boron bond, and indicate that the compound is best described as a borylborylene.}, language = {en} } @unpublished{AuerhammerArrowsmithBoehnkeetal.2018, author = {Auerhammer, Dominic and Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Dewhurst, Rian D. and Kupfer, Thomas}, title = {Brothers from Another Mother: a Borylene and its Dimer are Non-Interconvertible but Connected through Reactivity}, series = {Chemical Science}, journal = {Chemical Science}, doi = {10.1039/C7SC04789D}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157125}, year = {2018}, abstract = {The self-stabilizing, tetrameric cyanoborylene [(cAAC)B(CN)]4 (I, cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and its diborene relative, [(cAAC)(CN)B=B(CN)(cAAC)] (II), both react with disulfides and diselenides to yield the corresponding cAAC-supported cyanoboron bis(chalcogenides). Furthermore, reactions of I or II with elemental sulfur and selenium in various stoichiometries provided access to a variety of cAAC- stabilized cyanoboron-chalcogen heterocycles, including a unique dithiaborirane, a diboraselenirane, 1,3-dichalcogena-2,4-diboretanes, 1,3,4-trichalcogena- 2,5-diborolanes and a rare six-membered 1,2,4,5-tetrathia-3,6-diborinane. Stepwise addition reactions and solution stability studies provided insights into the mechanism of these reactions and the subtle differences in reactivity observed between I and II.}, language = {en} } @unpublished{BoehnkeBraunschweigJimenezHallaetal.2018, author = {B{\"o}hnke, Julian and Braunschweig, Holger and Jim{\´e}nez-Halla, Oscar and Krummenacher, Ivo and Stennett, Tom E.}, title = {Half-Sandwich Complexes of an Extremely Electron-Donating, Re-dox-Active η\(^6\)-Diborabenzene Ligand}, series = {Journal of the American Chemical Society}, journal = {Journal of the American Chemical Society}, doi = {10.1021/jacs.7b12394}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-156766}, year = {2018}, abstract = {The heteroarene 1,4-bis(CAAC)-1,4-diborabenzene (1; CAAC = cyclic (alkyl)(amino)carbene) reacts with [(MeCN)\(_3\)M(CO)\(_3\)] (M = Cr, Mo, W) to yield half-sandwich complexes of the form [(η\(^6\)-diborabenzene)M(CO)\(_3\)] (M = Cr (2), Mo (3), W (4)). Investigation of the new complexes with a combination of X-ray diffraction, spectroscopic methods and DFT calculations shows that ligand 1 is a remarkably strong electron donor. In particular, [(η\(^6\)-arene)M(CO)\(_3\)] complexes of this ligand display the lowest CO stretching frequencies yet observed for this class of complex. Cyclic voltammetry on complexes 2-4 revealed one reversi- ble oxidation and two reversible reduction events in each case, with no evidence of ring-slippage of the arene to the η\(^4\) binding mode. Treatment of 4 with lithium metal in THF led to identification of the paramagnetic complex [(1)W(CO)\(_3\)]Li·2THF (5). Compound 1 can also be reduced in the absence of a transition metal to its dianion 1\(^{2-}\), which possesses a quinoid-type structure.}, language = {en} } @unpublished{AuerhammerArrowsmithBissingeretal.2017, author = {Auerhammer, Dominic and Arrowsmith, Merle and Bissinger, Philipp and Braunschweig, Holger and Dellermann, Theresa and Kupfer, Thomas and Lenczyk, Carsten and Roy, Dipak and Sch{\"a}fer, Marius and Schneider, Christoph}, title = {Increasing the Reactivity of Diborenes: Derivatization of NHC- Supported Dithienyldiborenes with Electron-Donor Groups}, series = {Chemistry, A European Journal}, journal = {Chemistry, A European Journal}, doi = {10.1002/chem.201704669}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-155419}, year = {2017}, abstract = {A series of NHC-supported 1,2-dithienyldiborenes was synthesized from the corresponding (dihalo)thienylborane NHC precursors. NMR and UV-vis spectroscopic data, as well as X-ray crystallographic analyses, were used to assess the electronic and steric influences on the B=B double bond of various NHCs and electron-donating substituents on the thienyl ligands. Crystallographic data showed that the degree of coplanarity of the diborene core and thienyl groups is highly dependent on the sterics of the substituents. Furthermore, any increase in the electron- donating ability of the substituents resulted in the destabilization of the HOMO and greater instability of the resulting diborenes.}, language = {en} } @unpublished{WangArrowsmithBraunschweigetal.2017, author = {Wang, Sunewang Rixin and Arrowsmith, Merle and Braunschweig, Holger and Dewhurst, Rian and Paprocki, Valerie and Winner, Lena}, title = {CuOTf-mediated intramolecular diborene hydroarylation}, series = {Chemical Communications}, journal = {Chemical Communications}, doi = {10.1039/C7CC07371B}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154055}, year = {2017}, abstract = {Upon complexation to CuOTf, a PMe\(_3\)-stabilized bis(9-anthryl) diborene slowly undergoes an intramolecular hydroarylation reaction at room temperature. Subsequent triflation of the B-H bond with CuOTf, followed by a PMe\(_3\) transfer, finally yields a cyclic sp\(^2\)-sp\(^3\) boryl-substituted boronium triflate salt.}, language = {en} } @article{ArrowsmithBoehnkeBraunschweigetal.2016, author = {Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Celik, Mehmet and Claes, Christina and Ewing, William and Krummenacher, Ivo and Lubitz, Katharina and Schneider, Christoph}, title = {Neutral Diboron Analogues of Archetypal Aromatic Species by Spontaneous Cycloaddition}, series = {Angewandte Chemie, International Edition}, volume = {55}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201602384}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-138226}, pages = {11271-11275}, year = {2016}, abstract = {Among the numerous routes organic chemists have developed to synthesize benzene derivatives and heteroaro- matic compounds, transition-metal-catalyzed cycloaddition reactions are the most elegant. In contrast, cycloaddition reactions of heavier alkene and alkyne analogues, though limited in scope, proceed uncatalyzed. In this work we present the first spontaneous cycloaddition reactions of lighter alkene and alkyne analogues. Selective addition of unactivated alkynes to boron-boron multiple bonds under ambient con- ditions yielded diborocarbon equivalents of simple aromatic hydrocarbons, including the first neutral 6 π-aromatic dibora- benzene compound, a 2  π-aromatic triplet biradical 1,3-dibor- ete, and a phosphine-stabilized 2  π-homoaromatic 1,3-dihydro- 1,3-diborete. DFT calculations suggest that all three com- pounds are aromatic and show frontier molecular orbitals matching those of the related aromatic hydrocarbons, C\(_6\)H\(_6\) and C\(_4\)H\(_4\)\(^{2+}\), and homoaromatic C\(_4\)H\(_5\)\(^+\).}, language = {en} } @article{ArrowsmithBoehnkeBraunschweigetal.2016, author = {Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Celik, Mehmet and Dellermann, Theresa and Hammond, Kai}, title = {Uncatalyzed Hydrogenation of First-Row Main Group Multiple Bonds}, series = {Chemistry, A European Journal}, volume = {22}, journal = {Chemistry, A European Journal}, number = {48}, doi = {10.1002/chem.201604094}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-139364}, pages = {17169 -- 17172}, year = {2016}, abstract = {Room temperature hydrogenation of an SIDep-stabilized diboryne (SIDep = 1,3-bis(diethylphenyl)-4,5-dihydroimidazol-2-ylidene) and a CAAC-supported diboracumulene (CAAC = 1-(2,6- diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) provided the first selective route to the corresponding 1,2-dihydrodiborenes. DFT calculations showed an overall exothermic (ΔG = 19.4 kcal mol\(^{-1}\) two-step asynchronous H\(_2\) addition mechanism proceeding via a bridging hydride.}, subject = {Diborane}, language = {en} } @unpublished{ArrowsmithBoehnkeBraunschweigetal.2017, author = {Arrowsmith, Merle and B{\"o}hnke, Julian and Braunschweig, Holger and Celik, Mehmet Ali}, title = {Reactivity of a Dihydrodiborene with CO: Coordination, Insertion, Cleavage and Spontaneous Cyclic Alkyne Formation}, series = {Angewandte Chemie, International Edition}, journal = {Angewandte Chemie, International Edition}, doi = {10.1002/anie.201707907}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153318}, year = {2017}, abstract = {Under a CO atmosphere the dihydrodiborene [(cAAC)HB=BH(cAAC)] underwent coordination of CO concomitant with reversible hydrogen migration from boron to the carbene carbon atom, as well as reversible CO insertion into the B=B bond. Heating of the CO-adduct resulted in two unusual cAAC ring-expansion products, one presenting a B=C bond to a six-membered 1,2-azaborinane-3-ylidene, the other an unprecedented nine-membered cyclic alkyne resulting from reductive cleavage of CO and spontaneous C≡C triple bond formation.}, language = {en} }