Reactions of Tri- tert -Butylphosphatetrahedrane as a Spring-Loaded Phosphinidene Synthon Featuring Nickel-Catalyzed Transfer to Unactivated Alkenes.

Cage-opening reactions of the highly strained tri- tert -butylphosphatetrahedrane ( 1 ), shown here to function as a synthon of (tri- tert -butylcyclopropenyl)phosphinidene, are described. Treatment of 1 with a base-stabilized silylene led to the corresponding phosphasilene, which was isolated in 72% yield as a red crystalline solid. Phosphinidene transfer was also observed when 1 (2 equiv) was combined with the Wittig reagent Ph 3 PCH 2 to form a diphosphirane (50% isolated yield). The reaction is proposed to proceed through a generated phosphaalkene intermediate, which was characterized by NMR spectroscopy. In addition, we report on nickel-catalyzed phosphinidene transfer to styrene, ethylene, neohexene, and 1,3-cyclohexadiene; the corresponding phosphiranes were isolated in 51-64% yield. Computational studies suggest the intermediacy of a nickel phosphinidene species. Treatment of the ethylene-derived phosphirane product with triflic acid delivered elimination of [ t Bu 3 C 3 ]OTf and formation of a P-H bond, illustrating the ability of the tri- tert -butyl cyclopropenyl group to serve as a protecting group that is removable following phosphinidene transfer.