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.