A new method to prepare functional phosphines through steady‐state photolysis of triarylphosphines

Abstract

AbstractThe steady‐state photolysis of triarylphosphine, Ar3P, was carried out using a xenon lamp or a high‐pressure mercury lamp under an argon atmosphere in a solvent containing a functional group, CH3X. Gas chromatograph‐mass spectroscopic analysis on the photolysis showed that a phosphine to which the functional group from the solvent is incorporated, Ar2PCH2X, was formed in a moderate yield, along with tetraaryldiphosphine, Ar2PPAr2. The product, Ar2PCH2CN, from the photolysis in acetonitrile (X=CN) was isolated by column chromatography. In the photolysis in other solvents tried here (ethyl acetate, acetone, 2‐butanone, and 3,3‐dimethyl‐2‐butanone), Ar2PCH2X formed in the reaction mixture was so labile on a silica‐gel column that it was treated with S8 powder to convert to the corresponding phosphine sulfide, Ar2P(=S)CH2X. The resulting phosphine sulfide was isolated by column chromatography. The isolated products in these reactions, Ar2PCH2CN and Ar2P(=S)CH2X, were characterized by 1H, 13C, and 31P NMR spectroscopy, IR spectroscopy, and elemental analysis or high‐resolution mass spectroscopy. The formation of Ar2PCH2X as well as Ar2PPAr2 is explained by homolytic cleavage of a P‐C bond of Ar3P in the photoexcited state. This reactivity of Ar3P in the photoexcited state is in sharp contrast to that exerted under aerobic conditions, where Ar3P in the photoexcited state donates readily an electron to oxygen producing the radical cation, Ar3P·+. This photoreaction, which affords a functional phosphine, Ar2PCH2X, in one‐pot with generating very small amounts of unidentified side products, has potential for use in preparing functional phosphines.