Olefin Isomerization and Hydrosilylation Catalysis by Lewis Acidic Organofluorophosphonium Salts

Organofluorophosphonium salts of the formula [(C₆F₅)_3–<i>x</i>Ph_<i>x</i>PF]­[B­(C₆F₅)₄] (<i>x</i> = 0, 1) exhibit Lewis acidity derived from a low-lying σ* orbital at P opposite F. This acidity is evidenced by the reactions of these salts with olefins, which catalyze the rapid isomerization of 1-hexene to 2-hexene, the cationic polymerization of isobutylene, and the Friedel–Crafts-type dimerization of 1,1-diphenylethylene. In the presence of hydrosilanes, olefins and alkynes undergo efficient hydrosilylation catalysis to the alkylsilanes. Experimental and computational considerations of the mechanism are consistent with the sequential activation and 1,2-addition of hydrosilane across the unsaturated C–C bonds