Photochemical Alkene Hydrophosphination with Bis(trichlorosilyl)phosphine

Bis(trichlorosilyl)phosphine (HP(SiCl3)2, 1) was prepared from [TBA][P(SiCl3)2] ([TBA]2, TBA = tetra-n-butylammonium) and triflic acid in 36% yield. Phosphine 1 is an efficient reagent for hydrophosphination of unactivated terminal olefins under UV irradiation (15-60 min) and gives rise to bis(trichlorosilyl)alkylphosphines (RP(SiCl3)2, R = (CH2)5CH3, 88%; (CH2)7CH3, 98%; (CH2)2C(CH3)3, 76%; CH2Cy, 93%; (CH2)2Cy, 95%; CH2CH(CH3)(CH2)2CH3, 82%; (CH2)3O(CH2)3CH3, 95%; (CH2)3Cl, 83%; (CH2)2SiMe3, 92%; (CH2)5C(H)CH2, 44%) in excellent yields. The products require no further purification beyond filtration and removal of volatile material under reduced pressure. The P-Si bonds of prototypical products RP(SiCl3)2 (R = -(CH2)5CH3, -(CH2)7CH3) are readily functionalized to give further phosphorus-containing products: H3C(CH2)7PCl2 (56%), [H3C(CH2)5P(CH2Ph)3]Br (84%), H3C(CH2)7PH2 (61%), H3C(CH2)5P(O)(H)(OH) (81%), and H3C(CH2)5P(O)(OH)2 (55%). Experimental mechanistic investigations, accompanied by quantum chemical calculations, point toward a radical-chain mechanism. Phosphine 1 enables the fast, high-yielding, and atom-efficient preparation of compounds that contain phosphorus-carbon bonds in procedures that bypass white phosphorus (P4), a toxic and high-energy intermediate of the phosphorus industry.