Isolation of an Arsenic Diradicaloid with a Cyclic C(2)As(2)‐Core

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‐iPr(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.