Highly Strained Arene-Fused 1,2-Diborete Biradicaloid

Abstract

The stepwise reduction of a doubly cyclic alkyl(amino)carbene (CAAC)-stabilized 2,3-bis(dibromoboryl)naphthalene enables the isolation of the corresponding mono- and bis(boryl) radicals (one- and two-electron reduction), a 2π-aromatic 1,2-diborete (four-electron reduction), which shows biradical character in the solid-state EPR spectrum, and its cyclic bis(alkylidene)diboron dianion (six-electron reduction). The X-ray crystallographic analysis of the diborete shows a highly strained and twisted four-membered ring with a formal cis-diborene motif featuring a very elongated B–B double bond. Calculations based on DFT and multireference approaches reveal that the diborete possesses an open-shell singlet biradicaloid ground state, which is slightly energetically preferred to its EPR-active triplet-state congener. The addition of CO to the diborete resulted in B–B bond splitting and the formation of the corresponding closed-shell singlet, doubly Lewis base-stabilized bis(borylene), whereas a twofold γ insertion of phenyl azide generates a 1,3-bis(diazenyl)-1,3,2,4-diazadiboretidine.

Structure and Electronics of a Series of CAAC-Stabilized Diboron-Doped Acenes from 1,4-Diboranaphthalene to 6,13-Diborapentacene

“… DFT calculations show that 9,10-(CAAC) 2 -DBA exhibits an OSS biradical GS with a very small S–T gap of only 0.14 kcal mol –1 and a large closed-to-open shell singlet (C-OS) gap of −12.6 kcal mol –1 . The open-shell character of 9,10-(CAAC) 2 -DBA is favored by the two strongly π-accepting CAAC ligands, which help stabilize the unpaired electrons in radical main-group systems. − Like its NHC analogue, 9,10-(CAAC) 2 -DBA activates O 2 via a [4 + 2] cycloaddition, as well as sulfur and selenium to form S- and Se-bridged 9,10-DHDBA compounds, respectively …”

BN‐Butafulvenes and Their Application in the Synthesis of Highly Substituted BN‐9,1‐Naphthalenes

“…According to our computational results, BN‐butafulvene III lies much higher in free energy than BN‐benzene IV (Δ G =31.4 kcal mol −1 ) and BN‐pentafulvene V (Δ G =17.1 kcal mol −1 ) at G4MP2 (see Supporting Information for more details), a stability order consistent with the carbonaceous counterparts [5] . Likewise, III is synthetically challenging due to the inherent ring strain, which is nevertheless a fascinating feature that is extensively applied in synthetic chemistry [23–33] …”

“…[5] Likewise, III is synthetically challenging due to the inherent ring strain, which is nevertheless a fascinating feature that is extensively applied in synthetic chemistry. [23][24][25][26][27][28][29][30][31][32][33] Recently, we have spent effort on developing the coordination chemistry of bis(alkynyl)boranes, which led to success in the isolation of two different types of metallaboracycles. [34,35] One of them, the urana-borabicyclic complex, which was obtained by treating the uranacyclopropene complex [(C 5 Me 5 ) 2 U{η 2 -1,2-C 2 (SiMe 3 ) 2 }] (1) with Bamino bis(alkynyl)borane (Me 3 Si) 2 NB(C�CPh) 2 , comprises a BN-butafulvene unit that is fused to a Cp* 2 U (Cp* = pentamethylcyclopentadienyl) fragment.…”

BN‐Butafulvene und ihre Anwendung in der Synthese von hochsubstituierten BN‐9,1‐Naphthalinen

“…Nach unseren quantenchemischen Ergebnissen liegt die freie Reaktionsenthalpie von BN‐Butafulven III deutlich höher als die von BN‐Benzol IV (Δ G =31.4 kcal mol −1 ) und BN‐Pentafulven V (Δ G =17.1 kcal mol −1 ) bei G4MP2 (siehe Hintergrundinformationen für weitere Einzelheiten), eine Reihenfolge der Stabilität, die mit den kohlenstoffhaltigen Gegenstücken übereinstimmt [5] . Außerdem ist III aufgrund der inhärenten Ringspannung eine synthetische Herausforderung, die jedoch eine faszinierende Eigenschaft darstellt, die in der synthetischen Chemie ausgiebig genutzt wird [23–33] …”

“…[5] Außerdem ist III aufgrund der inhärenten Ringspannung eine synthetische Herausforderung, die jedoch eine faszinierende Eigenschaft darstellt, die in der synthetischen Chemie ausgiebig genutzt wird. [23][24][25][26][27][28][29][30][31][32][33] In jüngster Zeit haben wir uns mit der Entwicklung der Koordinationschemie von Bis(alkinyl)boranen befasst, was zur erfolgreichen Isolierung von zwei verschiedenen Arten von Metallaboracyclen geführt hat. [34,35] Einer von ihnen ist ein urana-bicyclischer Komplex, der durch Behandlung des Uranacyclopropen-Komplexes [(C 5 Me 5 ) 2 U{η 2 -1,2-C 2 -(SiMe 3 ) 2 }] (1) mit B-Aminobis(alkinyl)boran (Me 3 Si) 2 NB-(C�CPh) 2 erhalten wurde, umfasst eine BN-Butafulven-Einheit, die an ein Cp* 2 U-Fragment (Cp* = Pentamethylcyclopentadienyl) gebunden ist.…”