TY  - JOUR
A1  - Weiser, Jonas
A1  - Cui, Jingjing
A1  - Dewhurst, Rian D.
A1  - Braunschweig, Holger
A1  - Engels, Bernd
A1  - Fantuzzi, Felipe
T1  - Structure and bonding of proximity‐enforced main‐group dimers stabilized by a rigid naphthyridine diimine ligand
JF  - Journal of Computational Chemistry
N2  - 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.
KW  - bond theory
KW  - computational chemistry
KW  - density functional calculations
KW  - main group elements
KW  - N ligands
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312586
VL  - 44
IS  - 3
SP  - 456
EP  - 467
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  - Härterich, Marcel
A1  - Matler, Alexander
A1  - Dewhurst, Rian D.
A1  - Sachs, Andreas
A1  - Oppel, Kai
A1  - Stoy, Andreas
A1  - Braunschweig, Holger
T1  - A step-for-step main-group replica of the Fischer carbene synthesis at a borylene carbonyl
JF  - Nature Communications
N2  - 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.
KW  - chemical bonding
KW  - ligands
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-357270
VL  - 14
ER  - 
TY  - JOUR
A1  - Witte, Robert
A1  - Arrowsmith, Merle
A1  - Lamprecht, Anna
A1  - Schorr, Fabian
A1  - Krummenacher, Ivo
A1  - Braunschweig, Holger
T1  - C−C and C−N Bond Activation, Lewis‐Base Coordination and One‐ and Two‐Electron Oxidation at a Linear Aminoborylene
JF  - Chemistry – A European Journal
N2  - 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.
KW  - bond activation
KW  - boraselenone
KW  - dicoordinate borylene
KW  - one-electron oxidation
KW  - push-pull stabilization
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312491
VL  - 29
IS  - 16
ER  - 
TY  - JOUR
A1  - Brückner, Tobias
A1  - Ritschel, Benedikt
A1  - Jiménez‐Halla, J. Oscar C.
A1  - Fantuzzi, Felipe
A1  - Duwe, Dario
A1  - Markl, Christian
A1  - Dewhurst, Rian D.
A1  - Dietz, Maximilian
A1  - Braunschweig, Holger
T1  - Metal‐Free Intermolecular C−H Borylation of N‐Heterocycles at B−B Multiple Bonds
JF  - Angewandte Chemie International Edition
N2  - 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.
KW  - Boron
KW  - Borylation
KW  - Carbene
KW  - Diboryne
KW  - Hydroarylation
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312385
VL  - 62
IS  - 5
ER  - 
TY  - JOUR
A1  - Full, Felix
A1  - Wölflick, Quentin
A1  - Radacki, Krzysztof
A1  - Braunschweig, Holger
A1  - Nowak‐Król, Agnieszka
T1  - Enhanced Optical Properties of Azaborole Helicenes by Lateral and Helical Extension
JF  - Chemistry – A European Journal
N2  - 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.
KW  - azaborole
KW  - circularly polarized luminescence
KW  - fluorescence
KW  - helicene
KW  - π-extension
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293671
VL  - 28
IS  - 62
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  - Lu, Wei
A1  - Jayaraman, Arumugam
A1  - Fantuzzi, Felipe
A1  - Dewhurst, Rian D.
A1  - Härterich, Marcel
A1  - Dietz, Maximilian
A1  - Hagspiel, Stephan
A1  - Krummenbacher, Ivo
A1  - Hammond, Kai
A1  - Cui, Jingjing
A1  - Braunschweig, Holger
T1  - An unsymmetrical, cyclic diborene based on a chelating CAAC ligand and its small-molecule activation and rearrangement chemistry
JF  - Angewandte Chemie International Edition
N2  - 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.
KW  - inorganic chemistry
KW  - thermal rearrangement
KW  - alkylideneborane
KW  - carbene
KW  - diborene
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256576
VL  - 61
IS  - 3
ER  - 
TY  - JOUR
A1  - Dietz, Maximilian
A1  - Arrowsmith, Merle
A1  - Reichl, Stephan
A1  - Lugo‐Fuentes, Leonardo I.
A1  - Jiménez‐Halla, J. Oscar C.
A1  - Scheer, Manfred
A1  - Braunschweig, Holger
T1  - Stable Two‐Legged Parent Piano‐Stool and Mixed Diborabenzene‐E\(_{4}\) (E=P, As) Sandwich Complexes of Group 8
JF  - Angewandte Chemie International Edition
N2  - 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.
KW  - 1,4-Diborabenzene
KW  - bonding
KW  - group 8 metals
KW  - Parent Piano-Stool Complex
KW  - Pnictogen reduction
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293880
VL  - 61
IS  - 36
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  -