@unpublished{StennettBissingerGriesbecketal.2019, author = {Stennett, Tom E. and Bissinger, Philipp and Griesbeck, Stefanie and Ullrich, Stefan and Krummenacher, Ivo and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 Both molecules also display weak near-IR fluorescence with small Stokes shifts.}, language = {en} } @unpublished{EnglertStoyArrowsmithetal.2019, author = {Englert, Lukas and Stoy, Andreas and Arrowsmith, Merle and M{\"u}ssig, Jonas H. and Thaler, Melanie and Deißenberger,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} } @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{HanftRadackiLichtenberg2021, author = {Hanft, Anna and Radacki, Krzysztof and Lichtenberg, Crispin}, title = {Cationic Bismuth Aminotroponiminates: Charge Controls Redox Properties}, series = {Chemistry - A European Journal}, volume = {27}, journal = {Chemistry - A European Journal}, number = {20}, doi = {10.1002/chem.202005186}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225669}, pages = {6230 -- 6239}, year = {2021}, abstract = {The behavior of the redox-active aminotroponiminate (ATI) ligand in the coordination sphere of bismuth has been investigated in neutral and cationic compounds, [Bi(ATI)\(_{3}\)] and [Bi(ATI)\(_{2}\)L\(_{n}\)][A] (L=neutral ligand; n=0, 1; A=counteranion). Their coordination chemistry in solution and in the solid state has been analyzed through (variable-temperature) NMR spectroscopy, line-shape analysis, and single-crystal X-ray diffraction analyses, and their Lewis acidity has been evaluated by using the Gutmann-Beckett method (and modifications thereof). Cyclic voltammetry, in combination with DFT calculations, indicates that switching between ligand- and metal-centered redox events is possible by altering the charge of the compounds from 0 in neutral species to +1 in cationic compounds. This adds important facets to the rich redox chemistry of ATIs and to the redox chemistry of bismuth compounds, which is, so far, largely unexplored.}, 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{PhilippKrahfussRadackietal.2021, author = {Philipp, Michael S. M. and Krahfuss, Mirjam J. and Radacki, Krzysztof and Radius, Udo}, title = {N-Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Antimony(III)}, series = {European Journal of Inorganic Chemistry}, volume = {2021}, journal = {European Journal of Inorganic Chemistry}, number = {38}, doi = {10.1002/ejic.202100632}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257408}, pages = {4007-4019}, year = {2021}, abstract = {A systematic study on Lewis-acid/base adducts of N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC\(^{Me}\) (1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) with antimony(III) chlorides of the general formula SbCl\(_{2}\)R (R=Cl, Ph, Mes) is presented. The reaction of the NHCs Me\(_{2}\)Im\(^{Me}\) (1,3,4,5-tetra-methyl-imidazolin-2-ylidene), iPr\(_{2}\)Im\(^{Me}\) (1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene), Mes\(_{2}\)Im, Dipp\(_{2}\)Im (R\(_{2}\)Im=1,3-di-organyl-imidazolin-2-ylidene; Mes=2,4,6-trimethylphenyl, Dipp=2,6-di-isopropylphenyl) and cAAC\(^{Me}\) with antimony(III) compounds SbCl\(_{2}\)R (R=Cl (1), Ph (2) and Mes (3)) yields the adducts NHC ⋅ SbCl\(_{2}\)R (R=Cl (4), Ph (5) and Mes (6); NHC=Me\(_{2}\)Im\(^{Me}\) (a), iPr\(_{2}\)Im\(^{Me}\) (b), Dipp\(_{2}\)Im (c) and Mes\(_{2}\)Im (d)) and cAAC\(^{Me}\) ⋅ SbCl\(_{2}\)R (R=Cl (4 e) and Ph (5 e)). Thermal treatment of (Dipp\(_{2}\)Im) ⋅ SbCl\(_{2}\)Ar (Ar=Ph (5 c) and Mes (6 c)) in benzene leads to isomerization to the backbone coordinated \(^{a}\)NHC-adduct \(^{a}\)Dipp\(_{2}\)Im ⋅ SbCl\(_{2}\)Ar (Ar=Mes (7) and Ph (8)) (\(^{"a"}\) denotes "abnormal" coordination mode of the NHC) in high yields. One of the chloride substituents at antimony of 7 can be abstracted by GaCl3 or Ag[BF\(_{4}\)] to obtain the imidazolium salts [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][BF\(_{4}\)] (9) and [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][GaCl\(_{4}\)] (10).}, language = {en} } @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{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{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{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{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{HanftRottschaeferWieprechtetal.2021, author = {Hanft, Anna and Rottsch{\"a}fer, Dennis and Wieprecht, Nele and Geist, Felix and Radacki, Krzysztof and Lichtenberg, Crispin}, title = {Aminotroponiminates: Impact of the NO\(_{2}\) Functional Group on Coordination, Isomerisation, and Backbone Substitution}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {57}, doi = {10.1002/chem.202102324}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256988}, pages = {14250-14262}, year = {2021}, abstract = {Aminotroponiminate (ATI) ligands are a versatile class of redox-active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron-withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro-substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N-binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first "naked" (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N-coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT-)NMR spectroscopy, single-crystal X-ray diffraction analysis, and DFT calculations.}, 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} }