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