TY - JOUR A1 - Mützel, Carina A1 - Farrell, Jeffrey M. A1 - Shoyama, Kazutaka A1 - Würthner, Frank T1 - 12b,24b-Diborahexabenzo[a,c,fg,l,n,qr]pentacene: A Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbon JF - Angewandte Chemie International Edition N2 - Herein we devise and execute a new synthesis of a pristine boron-doped nanographene. Our target boron-doped nanographene was designed based on DFT calculations to possess a low LUMO energy level and a narrow band gap derived from its precise geometry and B-doping arrangement. Our synthesis of this target, a doubly B-doped hexabenzopentacene (B\(_{2}\)-HBP), employs six net C−H borylations of an alkene, comprising consecutive hydroboration/electrophilic borylation/dehydrogenation and BBr\(_{3}\)/AlCl\(_{3}\)/2,6-dichloropyridine-mediated C−H borylation steps. As predicted by our calculations, B\(_{2}\)-HBP absorbs strongly in the visible region and emits in the NIR up to 1150 nm in o-dichlorobenzene solutions. Furthermore, B\(_{2}\)-HBP possesses a very low LUMO level, showing two reversible reductions at −1.00 V and −1.17 V vs. Fc\(^{+}\)/Fc. Our methodology is surprisingly selective despite its implementation of unfunctionalized precursors and offers a new approach to the synthesis of pristine B-doped polycyclic aromatic hydrocarbons. KW - aromaticity KW - polycycles KW - pentacene KW - near infrared emitter KW - boron Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318808 VL - 61 IS - 8 ER - TY - JOUR A1 - Häring, Mathias A1 - Kerpen, Christoph A1 - Ribbeck, Tatjana A1 - Hennig, Philipp T. A1 - Bertermann, Rüdiger A1 - Ignat’ev, Nikolai V. A1 - Finze, Maik T1 - Dismutation of Tricyanoboryllead Compounds: The Homoleptic Tetrakis(tricyanoboryl)plumbate Tetraanion JF - Angewandte Chemie N2 - A series of unprecedently air-stable (tricyanoboryl)plumbate anions was obtained by the reaction of the boron-centered nucleophile B(CN)\(_{3}\)\(^{2-}\) with triorganyllead halides. Salts of the anions [R\(_{3}\)PbB(CN)\(_{3}\)]\(^{-}\) (R=Ph, Et) were isolated and found to be stable in air at room temperature. In the case of Me\(_{3}\)PbHal (Hal=Cl, Br), a mixture of the anions [Me\(_{4-n}\)Pb{B(CN)\(_{3}\)}\(_{n}\)]\(^{n-}\) (n=1, 2) was obtained. The [Et\(_{3}\)PbB(CN)\(_{3}\)]− ion undergoes stepwise dismutation in aqueous solution to yield the plumbate anions [Et4\(_{4-n}\)Pb{B(CN)\(_{3}\)}\(_{n}\)]\(^{n-}\) (n=1–4) and PbEt\(_{4}\) as by-product. The reaction rate increases with decreasing pH value of the aqueous solution or by bubbling O\(_{2}\) through the reaction mixture. Adjustment of the conditions allowed the selective formation and isolation of salts of all anions of the series [Et\(_{4-n}\)Pb{B(CN)\(_{3}\)}\(_{n}\)]\(^{n-}\) (n=2–4) including the homoleptic tetraanion [Pb{B(CN)\(_{3}\)}\(_{4}\)]\(^{4-}\). KW - anions KW - boron KW - cyanoborates KW - dismutations KW - lead Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318257 VL - 61 IS - 24 ER - TY - JOUR A1 - Bachmann, Jonas A1 - Helbig, Andreas A1 - Crumbach, Merian A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Helten, Holger T1 - Fusion of Aza‐ and Oxadiborepins with Furans in a Reversible Ring‐Opening Process Furnishes Versatile Building Blocks for Extended π‐Conjugated Materials JF - Chemistry – A European Journal N2 - 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. KW - aromaticity KW - boron KW - BN compounds KW - furan KW - polycycles Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293926 VL - 28 IS - 63 ER - TY - JOUR A1 - Zapf, Ludwig A1 - Peters, Sven A1 - Bertermann, Rüdiger A1 - Radius, Udo A1 - Finze, Maik T1 - Tricyanoborane‐Functionalized Anionic N‐Heterocyclic Carbenes: Adjustment of Charge and Stereo‐Electronic Properties JF - Chemistry – A European Journal N2 - The 1‐methyl‐3‐(tricyanoborane)imidazolin‐2‐ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3‐methylimidazole adduct 1. Regarding charge and stereo‐electronic properties, anion 2 closes the gap between well‐known neutral NHCs and the ditopic dianionic NHC, the 1,3‐bis(tricyanoborane)imidazolin‐2‐ylidenate dianion (IIb). The influence of the number of N‐bonded tricyanoborane moieties on the σ‐donating and π‐accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3‐dimethylimidazolin‐2‐ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)\(_{4}\)] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V\(_{bur}\)) and σ‐donor and π‐acceptor abilities of NHCs can be effectively fine‐tuned via the number of tricyanoborane substituents. KW - N-heterocyclic carbene KW - anionic carbene KW - boron KW - cyanoborate KW - imidazolate Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-287200 VL - 28 IS - 39 ER - TY - THES A1 - Hagspiel, Stephan Alexander T1 - Synthesis and Reactivity of Pseudohalide-substituted Boranes and Borylenes T1 - Synthese und Reaktivität Pseudohalogenid-substituierter Borane und Borylene N2 - This work involves the synthesis and reactivity of pseudohalide-substituted boranes and borylenes. A series of compounds of the type (CAAC)BR2Y (CAAC = cyclic alkyl(amino)carbene; R = H, Br; Y = CN, NCS, PCO) were prepared first. The two-electron reduction of (CAAC)BBr2Y (Y = CN, NCS) in the presence of a second Lewis base L (L = N-heterocyclic carbene) resulted in the formation of the corresponding doubly Lewis base-stabilized pseudohaloborylenes (CAAC)(L)BY. These borylenes show versatile reactivity patterns, including their oxidation to the corresponding radical cations, coordination via the respective pseudohalide substituent to group 6 metal carbonyl complexes, as well as a boron-centered protonation with Brønsted acids to boronium cations. Reduction of (CAAC)BBr2(NCS) in the absence of a second donor ligand, led to the formation of boron-doped thiazolothiazoles via reductive dimerization of two isothiocyanatoborylenes. These B,N,S-heterocycles possess a low degree of aromaticity as well as interesting photophysical properties and can furthermore be protonated as well as hydroborated. Additionally, CAAC adducts of the parent boraphosphaketene (CAAC)BH2(PCO) could be prepared, which readily reacted with boroles [Ph4BR'] (R' = aryl) via decarbonylation in a ring expansion reaction. The obtained 1,2-phosphaborinines represent B,P-isosteres of benzene and consequently could be coordinated to metal carbonyl complexes of the chromium triade via η6-coordination, resulting in new half-sandwich complexes thereof. N2 - Diese Arbeit beinhaltet die Synthese und Reaktivität von Pseudohalogenid-substituierten Boranen und Borylenen. Dabei wurde zunächst eine Reihe an Verbindungen des Typs (CAAC)BR2Y (CAAC = cyclisches Alkyl(amino)carben; R = H, Br; Y = CN, NCS, PCO) dargestellt. Die Zweielektronenreduktion von (CAAC)BBr2Y (Y = CN, NCS) in der Gegenwart einer weiteren Lewis-Base L (L = N-heterocyclisches Carben) resultierte in der Bildung der entsprechenden zweifach Lewis-Basen-stabilisierten Pseudohalogenborylene (CAAC)(L)BY. Diese Borylene zeigen eine vielseitige Folgechemie, wobei sie zu den korrespondierenden Radikalkationen oxidiert, über den jeweiligen Pseudohalogenidsubstituenten an Metallcarbonylkomplexe der Gruppe 6 koordiniert sowie mit Brønsted-Säuren Bor-zentriert zu Boroniumkationen protoniert werden können. Die Reduktion von (CAAC)BBr2(NCS) in Abwesenheit eines weiteren Donorliganden führte über die reduktive Dimerisierung zweier Isothiocyanatoborylene zur Bildung Bor-dotierter Thiazolothiazole. Diese B,N,S-Heterocyclen verfügen über ein geringes Ausmaß an Aromatizität sowie interessante photophysikalische Eigenschaften, und können darüber hinaus protoniert wie auch hydroboriert werden. Des Weiteren konnten CAAC-Addukte des Stammboraphosphaketens (CAAC)BH2(PCO) dargestellt werden, die bereitwillig unter Decarbonylierung in einer Ringerweiterungsreaktion mit Borolen [Ph4BR‘] (R‘ = Aryl) reagieren. Die erhaltenen 1,2-Phosphaborinine stellen B,P-Isostere des Benzols dar und konnten folglich über eine η6-Koordination an Metallcarbonylkomplexe der Chromtriade koordiniert werden, woraus neue Halbsandwichkomplexe dieser resultierten. KW - Borylene KW - Pseudohalogenide KW - Heteroaromaten KW - boron KW - pseudohalides KW - heterocycles KW - aromaticity KW - DFT KW - Bor KW - Pseudohalogenide KW - Heterocyclen KW - Aromatizität KW - DFT Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-249459 ER - TY - JOUR A1 - Huang, Mingming A1 - Hu, Jiefeng A1 - Krummenacher, Ivo A1 - Friedrich, Alexandra A1 - Braunschweig, Holger A1 - Westcott, Stephen A. A1 - Radius, Udo A1 - Marder, Todd B. T1 - Base-Mediated Radical Borylation of Alkyl Sulfones JF - Chemistry—A European Journal N2 - 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. KW - boron KW - boronate KW - boronic acid KW - metal-free KW - radical Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257281 VL - 28 IS - 3 ER - TY - JOUR A1 - Schorr, Fabian A1 - Schopper, Nils A1 - Riensch, Nicolas A1 - Fantuzzi, Felipe A1 - Neder, Marco A1 - Dewhurst, Rian D. A1 - Thiess, Thorsten A1 - Brückner, Tobias A1 - Hammond, Kai A1 - Helten, Holger A1 - Finze, Maik A1 - Braunschweig, Holger T1 - Controlled Synthesis of Oligomers Containing Main-Chain B(sp\(^{2}\))-B(sp\(^{2}\)) Bonds JF - Chemistry—A European Journal N2 - 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. KW - oligomerization KW - boron KW - catenation KW - diborane KW - hydroboration Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257274 VL - 27 IS - 64 ER - TY - JOUR A1 - Cui, Jingjing A1 - Dietz, Maximilian A1 - Härterich, Marcel A1 - Fantuzzi, Felipe A1 - Lu, Wei A1 - Dewhurst, Rian D. A1 - Braunschweig, Holger T1 - Diphosphino-Functionalized 1,8-Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes JF - Chemistry—A European Journal N2 - 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. KW - pincer ligand KW - potassium reagent KW - diborane KW - naphthyridine KW - boron Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256994 VL - 27 IS - 63 ER - TY - JOUR A1 - Berger, Sarina M. A1 - Rühe, Jessica A1 - Schwarzmann, Johannes A1 - Phillipps, Alexandra A1 - Richard, Ann-Katrin A1 - Ferger, Matthias A1 - Krummenacher, Ivo A1 - Tumir, Lidija-Marija A1 - Ban, Željka A1 - Crnolatac, Ivo A1 - Majhen, Dragomira A1 - Barišić, Ivan A1 - Piantanida, Ivo A1 - Schleier, Domenik A1 - Griesbeck, Stefanie A1 - Friedrich, Alexandra A1 - Braunschweig, Holger A1 - Marder, Todd B. T1 - 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 JF - Chemistry—A European Journal N2 - 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. KW - singlet oxygen KW - boron KW - bioimaging KW - luminescence KW - nucleic acid Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256963 VL - 27 IS - 56 ER - TY - JOUR A1 - Gärtner, Annalena A1 - Marek, Matthäus A1 - Arrowsmith, Merle A1 - Auerhammer, Dominic A1 - Radacki, Krzysztof A1 - Prieschl, Dominic A1 - Dewhurst, Rian D. A1 - Braunschweig, Holger T1 - Boron- versus Nitrogen-Centered Nucleophilic Reactivity of (Cyano)hydroboryl Anions: Synthesis of Cyano(hydro)organoboranes and 2-Aza-1,4-diborabutatrienes JF - Chemistry—A European Journal N2 - 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. KW - nucleophile KW - boron KW - boryl anion KW - cumulene Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256853 VL - 27 IS - 37 ER - TY - JOUR A1 - Schmidt, Paul A1 - Fantuzzi, Felipe A1 - Klopf, Jonas A1 - Schröder, Niklas B. A1 - Dewhurst, Rian D. A1 - Braunschweig, Holger A1 - Engel, Volker A1 - Engels, Bernd T1 - Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics JF - Chemistry - A European Journal N2 - 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. KW - chemistry KW - radicals KW - ab initio calculations KW - boron KW - carbene ligands KW - density functional calculations Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256636 VL - 27 IS - 16 ER - TY - JOUR A1 - Brückner, Tobias A1 - Fantuzzi, Felipe A1 - Stennett, Tom E. A1 - Krummenacher, Ivo A1 - Dewhurst, Rian D. A1 - Engels, Bernd A1 - Braunschweig, Holger T1 - Isolation of neutral, mono-, and dicationic B\(_2\)P\(_2\) rings by diphosphorus addition to a boron-boron triple bond JF - Angewandte Chemie International Edition N2 - 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. KW - inorganic chemistry KW - radicals KW - boron KW - density functional calculations KW - oxidation KW - phosphorus heterocycles Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256451 VL - 60 IS - 24 ER - TY - JOUR A1 - Hagspiel, Stephan A1 - Fantuzzi, Felipe A1 - Dewhurst, Rian D. A1 - Gärtner, Annalena A1 - Lindl, Felix A1 - Lamprecht, Anna A1 - Braunschweig, Holger T1 - Adducts of the parent boraphosphaketene H\(_2\)BPCO and their decarbonylative insertion chemistry JF - Angewandte Chemie International Edition N2 - 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. KW - inorganic chemistry KW - phosphorus KW - boron KW - decarbonylation KW - heterocycles KW - ketenes Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256470 VL - 60 IS - 24 ER - TY - JOUR A1 - Zapf, Ludwig A1 - Radius, Udo A1 - Finze, Maik T1 - 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion - a ditopic dianionic N-heterocyclic carbene ligand JF - Angewandte Chemie International Edition N2 - The 1,3-bis(tricyanoborane)imidazolate anion 1 was obtained in high yield from lithium imidazolate and B(CN)\(_3\)−pyridine adduct. Anion 1 is chemically very robust and thus allowed the isolation of the corresponding H\(_5\)O\(_2\)\(^+\) salt. Furthermore, monoanion 1 served as starting species for the novel dianionic N-heterocyclic carbene (NHC), 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion 3 that acts as ditopic ligand via the carbene center and the cyano groups at boron. First reactions of this new NHC 3 with methyl iodide, elemental selenium, and [Ni(CO)\(_4\)] led to the methylated imidazolate ion 4, the dianionic selenium adduct 5, and the dianionic nickel tricarbonyl complex 6. These NHC derivatives provide a first insight into the electronic and steric properties of the dianionic NHC 3. Especially the combination of properties, such as double negative charge, different coordination sites, large buried volume and good σ-donor and π-acceptor ability, make NHC 3 a unique and promising ligand and building block. KW - inorganic chemistry KW - N-heterocyclic carbene KW - anioniccarbene KW - boron KW - cyanoborate KW - imidazolate Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256498 VL - 60 IS - 33 ER - TY - JOUR A1 - Crumbach, Merian A1 - Bachmann, Jonas A1 - Fritze, Lars A1 - Helbig, Andreas A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Helten, Holger T1 - Dithiophene‐Fused Oxadiborepins and Azadiborepins: A New Class of Highly Fluorescent Heteroaromatics JF - Angewandte Chemie International Edition N2 - 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. KW - aromaticity KW - BN compounds KW - boron KW - isoelectronic analogues KW - polycycles Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-238996 VL - 60 IS - 17 SP - 9290 EP - 9295 ER - TY - JOUR A1 - Huang, Zhenguo A1 - Wang, Suning A1 - Dewhurst, Rian D. A1 - Ignat'ev, Nikolai V. A1 - Finze, Maik A1 - Braunschweig, Holger T1 - Boron: Its Role in Energy‐Related Processes and Applications JF - Angewandte Chemie International Edition N2 - 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. KW - boron KW - electrolytes KW - hydrogen KW - OLEDs KW - small-molecule activation Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218514 VL - 59 IS - 23 SP - 8800 EP - 8816 ER - TY - THES A1 - Crumbach, Merian T1 - Modifying the Optoelectronic Properties of Polycyclic Aromatic Hydrocarbons and Linear Oligomers by Doping with Boron and Further Heteroatoms T1 - Modifizierung der Optoelektronischen Eigenschaften von Polyzyklischen Aromatischen Kohlenwasserstoffen und Linearen Oligomeren durch Dotierung mit Bor und weiteren Heteroatomen N2 - Der Austausch ausgewählter CC-Einheiten durch ihre isoelektronischen und isosteren BN-Einheiten in π-konjugierten organischen Verbindungen (BN/CC-Isosterie), insbesondere in polyzyklischen aromatischen Kohlenwasserstoffen (PAKs), hat sich als erfolgreiche Strategie zur Herstellung neuartiger organisch-anorganischer Hybridmaterialien erwiesen, die strukturelle Ähnlichkeiten mit ihren reinen Kohlenstoff Analoga aufweisen, aber in vielen Fällen mit veränderten faszinierenden Eigenschaften und Funktionen. In den ersten beiden Kapiteln werden die Synthese und Eigenschaften von neuartigen BNB-dotierten Phenalenylen, Dithienoazadiborepinen und Dithienooxadiborepinen vorgestellt. Die optoelektronischen Eigenschaften dieser neuen Bauelemente können durch Variation der eingebauten Ar- (Mes, Tip, FMes) und R-Gruppen (H, Me, i-Pr, t-Bu, Ph) effektiv eingestellt werden. Theoretische Untersuchungen, einschließlich NICS (Nucleus Independent Chemical Shift) Scans und AICD (Anisotropy of the Induced Current Density)-Berechnungen, wurden durchgeführt und geben Einblick in ihren aromatischen oder antiaromatischen Charakter. Der Einbau von BP-Einheiten, welche mit BN und CC valenz-isoelektronisch sind, in ungesättigte organische Verbindungen ist dagegen bisher kaum untersucht worden, obwohl das Potenzial der resultierenden BCP-Hybridmaterialien für elektronische Anwendungen erst kürzlich erkannt wurde. Konjugierte Hauptkettenpolymere mit BP-Fragmenten im Rückgrat sind bisher unbekannt. Die ersten molekularen Modellverbindungen für ein BP-Analogon des konjugierten Polymers Poly(p-phenylen-vinylen) (PPV) werden in Kapitel 3 vorgestellt. Theoretische Untersuchungen ergaben, dass die Mes*-Gruppe das Phosphor-zentrum vollständig planarisiert, wodurch der B=P-Doppelbindungscharakter verstärkt und eine Konjugation über die BP-Einheit ermöglicht wird. Es wurden verschiedene synthetische Ansätze zu diesen molekularen Modellverbindungen untersucht und eine erfolgreiche synthetische Strategie gefunden. N2 - The substitution of selected CC units by their isoelectronic and isosteric BN units in π−conjugated organic compounds (BN/CC isosterism), especially polycyclic aromatic hydrocarbons (PAHs), has emerged as a viable strategy to produce novel organic–inorganic hybrid materials with structural similarities to their all-carbon congeners, but in many cases with intriguing properties and functions. In the first two chapters the synthesis and properties of novel BNB-doped phenalenyls, dithienoazadiborepins and dithienooxadiborepins are presented. The optoelectronic properties of these new building blocks can be effectively tuned by variation of the incorporated Ar (Mes, Tip, FMes) and R groups (H, Me, i-Pr, t-Bu, Ph). Theoretical investigations, including NICS (Nucleus Independent Chemical Shift) scans and AICD (Anisotropy of the Induced Current Density) calculations, have been performed which provide insight into their aromatic or antiaromatic character, respectively. The incorporation of BP units, on the other hand, which are valence isoelectronic with BN and CC, into unsaturated organic compounds, has been scarcely studied, though the potential of the resulting BCP hybrid materials for electronic applications has been recognized quite recently. Main chain conjugated polymers featuring BP fragments in the backbone are unknown so far. The first molecular model compounds for a BP analogue of the conjugated polymer poly(p-phenylene vinylene) (PPV) are presented in chapter 3. Theoretical investigations revealed that the Mes* group to fully planarizes the phosphorus center, increasing the B=P double bond character and enabling conjugation over the BP unit. Different synthetic approaches to the molecular model compounds have been investigated and a viable synthetic strategy was found. KW - Aromatizität KW - Isoelektronisches Prinzip KW - Polycyclische Aromaten KW - Oligomere KW - Bor KW - BN compounds KW - boron KW - BP compounds KW - polycycles KW - oligomers KW - Bor-Stickstoff-Verbindungen KW - Bor KW - Bor-Phosphor-Verbindungen KW - Polyzyklen KW - Oligomere Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-242845 ER - TY - JOUR A1 - Saalfrank, Christian A1 - Fantuzzi, Felipe A1 - Kupfer, Thomas A1 - Ritschel, Benedikt A1 - Hammond, Kai A1 - Krummenacher, Ivo A1 - Bertermann, Rüdiger A1 - Wirthensohn, Raphael A1 - Finze, Maik A1 - Schmid, Paul A1 - Engel, Volker A1 - Engels, Bernd A1 - Braunschweig, Holger T1 - cAAC‐Stabilized 9,10‐diboraanthracenes—Acenes with Open‐Shell Singlet Biradical Ground States JF - Angewandte Chemie International Edition N2 - 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. KW - acenes KW - biradicals KW - bond Activation KW - boron KW - heterocycles Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-217795 VL - 59 IS - 43 SP - 19338 EP - 19343 ER - TY - JOUR A1 - Rauch, Florian A1 - Fuchs, Sonja A1 - Friedrich, Alexandra A1 - Sieh, Daniel A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Finze, Maik A1 - Marder, Todd B. T1 - Highly Stable, Readily Reducible, Fluorescent, Trifluoromethylated 9‐Borafluorenes JF - Chemistry – A European Journal N2 - 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. KW - borafluorenes KW - boron KW - EPR spectroscopy KW - fluorescence KW - heterocycles Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218390 VL - 26 IS - 56 SP - 12794 EP - 12808 ER - TY - JOUR A1 - Hermann, Alexander A1 - Fantuzzi, Felipe A1 - Arrowsmith, Merle A1 - Zorn, Theresa A1 - Krummenacher, Ivo A1 - Ritschel, Benedikt A1 - Radacki, Krzysztof A1 - Engels, Bernd A1 - Braunschweig, Holger T1 - Oxidation, Coordination, and Nickel-Mediated Deconstruction of a Highly Electron-Rich Diboron Analogue of 1,3,5-Hexatriene JF - Angewandte Chemie, International Edition N2 - 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). KW - boron KW - diborenes KW - carbenes KW - conjugation KW - density-functional calculations KW - rearrangements KW - structure elucidation Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-240652 VL - 59 IS - 36 ER -