Reactions of Tri-tert-Butylphosphatetrahedrane as a Spring-LoadedPhosphinidene Synthon Featuring Nickel-Catalyzed Transfer toUnactivated Alkenes

Cage-opening reactions of the highly strained tri-tert-butylphosphatetrahedrane (1), shown here to function as asynthon of (tri-tert-butylcyclopropenyl)phosphinidene, are described. Treatment of1with a base-stabilized silylene led to thecorresponding phosphasilene, which was isolated in 72% yield as a red crystalline solid. Phosphinidene transfer was also observedwhen1(2 equiv) was combined with the Wittig reagent Ph3PCH2to form a diphosphirane (50% isolated yield). The reaction isproposed 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 correspondingphosphiranes 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 [tBu3C3]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 followingphosphinidene transfer.

Automated summary

Cage-opening reactions and phosphinidene transfer of highly strained tri-tert-butylphosphatetrahedrane were described. Nickel-catalyzed phosphinidene transfer to various substrates was also investigated, revealing the removable protecting ability of the tri-tert-butyl cyclopropenyl group.