Photochemical Alkene Hydrophosphination with Bis(trichlorosilyl)phosphine.

Bis(trichlorosilyl)phosphine (HP(SiCl 3 ) 2 , 1 ) was prepared from [TBA][P(SiCl 3 ) 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(SiCl 3 ) 2 , R = (CH 2 ) 5 CH 3 , 88%; (CH 2 ) 7 CH 3 , 98%; (CH 2 ) 2 C(CH 3 ) 3 , 76%; CH 2 Cy, 93%; (CH 2 ) 2 Cy, 95%; CH 2 CH(CH 3 )(CH 2 ) 2 CH 3 , 82%; (CH 2 ) 3 O(CH 2 ) 3 CH 3 , 95%; (CH 2 ) 3 Cl, 83%; (CH 2 ) 2 SiMe 3 , 92%; (CH 2 ) 5 C(H)CH 2 , 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(SiCl 3 ) 2 (R = -(CH 2 ) 5 CH 3 , -(CH 2 ) 7 CH 3 ) are readily functionalized to give further phosphorus-containing products: H 3 C(CH 2 ) 7 PCl 2 (56%), [H 3 C(CH 2 ) 5 P(CH 2 Ph) 3 ]Br (84%), H 3 C(CH 2 ) 7 PH 2 (61%), H 3 C(CH 2 ) 5 P(O)(H)(OH) (81%), and H 3 C(CH 2 ) 5 P(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 (P 4 ), a toxic and high-energy intermediate of the phosphorus industry.