TY - JOUR A1 - Roy, Dipak Kumar A1 - Tröster, Tobias A1 - Fantuzzi, Felipe A1 - Dewhurst, Rian D. A1 - Lenczyk, Carsten A1 - Radacki, Krzysztof A1 - Pranckevicius, Conor A1 - Engels, Bernd A1 - Braunschweig, Holger T1 - Isolation and Reactivity of an Antiaromatic s‐Block Metal Compound JF - Angewandte Chemie International Edition N2 - 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. KW - antiaromaticity KW - aromaticity KW - beryllium KW - heterocycles KW - s-block metals Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224447 VL - 60 IS - 7 SP - 3812 EP - 3819 ER - TY - JOUR A1 - Lindl, Felix A1 - Lamprecht, Anna A1 - Arrowsmith, Merle A1 - Khitro, Eugen A1 - Rempel, Anna A1 - Dietz, Maximilian A1 - Wellnitz, Tim A1 - Bélanger‐Chabot, Guillaume A1 - Stoy, Andreas A1 - Paprocki, Valerie A1 - Prieschl, Dominik A1 - Lenczyk, Carsten A1 - Ramler, Jacqueline A1 - Lichtenberg, Crispin A1 - Braunschweig, Holger T1 - Aromatic 1,2‐Azaborinin‐1‐yls as Electron‐Withdrawing Anionic Nitrogen Ligands for Main Group Elements JF - Chemistry – A European Journal N2 - 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. KW - 1,2-azaborinine KW - aromaticity KW - crystallographic analyses KW - N-functionalization KW - salt metathesis Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312222 VL - 29 IS - 11 ER - TY - JOUR A1 - Hagspiel, Stephan A1 - Arrowsmith, Merle A1 - Fantuzzi, Felipe A1 - Vargas, Alfredo A1 - Rempel, Anna A1 - Hermann, Alexander A1 - Brückner, Tobias A1 - Braunschweig, Holger T1 - Highly colored boron-doped thiazolothiazoles from the reductive dimerization of boron isothiocyanates JF - Angewandte Chemie International Edition N2 - 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. KW - inorganic chemistry KW - aromaticity KW - reduction KW - fused thiazaboroles KW - DFT KW - borylenes Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256432 VL - 60 IS - 12 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 - 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 -