Reactions of Tri-<i>tert</i>-Butylphosphatetrahedrane as a Spring-Loaded Phosphinidene Synthon Featuring Nickel-Catalyzed Transfer to Unactivated Alkenes

Abstract

Cage-opening reactions of the highly strained tri-<i>tert</i>-butylphosphatetrahedrane (<b>1</b>), shown here to function as a synthon of (tri-<i>tert</i>-butylcyclopropenyl)phosphinidene, are described. Treatment of <b>1</b> 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 <b>1</b> (2 equiv) was combined with the Wittig reagent Ph₃PCH₂ 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 [^<i>t</i>Bu₃C₃]OTf and formation of a P-H bond, illustrating the ability of the tri-<i>tert</i>-butyl cyclopropenyl group to serve as a protecting group that is removable following phosphinidene transfer.