Geometrically Enforced Donor-Facilitated Dehydrocoupling Leading to an Isolable Arsanylidine-Phosphorane

A proximate Lewis basic group facilitates the mild dehydrogenative P–As intramolecular coupling in the phosphine-arsine peri-substituted acenaphthene <b>3</b>, affording thermally and hydrolytically stable arsanylidine-phosphorane <b>4</b> with a sterically accessible two-coordinate arsenic atom. The formation of <b>4</b> is thermoneutral due to the dehydrogenation being concerted with the donor coordination. Reaction of <b>4</b> with a limited amount of oxygen reveals arsinidene-like reactivity via formation of cyclooligoarsines, supporting the formulation of the bonding in <b>4</b> as base-stabilized arsinidene R₃P→AsR