Isolation of an Arsenic Diradicaloid with a Cyclic C₂As₂‐Core

Abstract

Abstract Herein, we report on the synthesis, characterization, and reactivity studies of the first cyclic C 2 As 2 ‐diradicaloid {(IPr)CAs} 2 ( 6 ) (IPr = C{N(Dipp)CH} 2 ; Dipp = 2,6‐ i Pr 2 C 6 H 3 ). Treatment of (IPr)CH 2 ( 1 ) with AsCl 3 affords the Lewis adduct {(IPr)CH 2 }AsCl 3 ( 2 ). Compound 2 undergoes stepwise dehydrochlorination to yield {(IPr)CH}AsCl 2 ( 3 ) and {(IPr)CAsCl} 2 ( 5 a ) or [{(IPr)CAs} 2 Cl]OTf ( 5 b ). Reduction of 5 a (or 5 b ) with magnesium turnings gives 6 as a red crystalline solid in 90% yield. Compound 6 featuring a planar C 2 As 2 ring is diamagnetic and exhibits well resolved NMR signals. DFT calculations reveal a singlet ground state for 6 with a small singlet‐triplet energy gap of 8.7 kcal mol −1 . The diradical character of 6 amounts to 20% (CASSCF, complete active space self consistent field) and 28% (DFT). Treatments of 6 with (PhSe) 2 and Fe 2 (CO) 9 give rise to {(IPr)CAs(SePh)} 2 ( 7 ) and {(IPr)CAs} 2 Fe(CO) 4 ( 8 ), respectively.