Isolation of an Arsenic Diradicaloid with a Cyclic C<sub>2</sub>As<sub>2</sub>‐Core
Henric Steffenfauseweh, Yury V. Vishnevskiy, Beate Neumann, Hans‐Georg Stammler, Diego M. Andrada, Rajendra S. Ghadwal
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.