P-C bond activation chemistry: Evidence for 1,1-carboboration reactions proceeding with phosphorus-carbon bond cleavage

Article abstract of DOI:10.1021/ja1110283

A series of diarylphosphinyl-substituted acetylenes of the type (aryl) ₂P-C≡C-R (aryl = phenyl or mesityl, R = Ph or n-propyl) react with the strongly Lewis acid reagent B(C₆F₅)₃ in toluene at elevated temperatures (70-105 °C) to give the 1,1-carboboration products 4. Treatment of bis(diphenylphosphinyl)acetylene with B(C₆F₅)₃ under analogous conditions proceeded with phosphinyl migration to yield the 1,1-carboboration product 4d, bearing a geminal pair of Ph₂P substituents at one former acetylene carbon atom and a C₆F₅ substituent and the remaining -B(C ₆F₅)₂ group at the other. Prolonged thermolysis of 4d resulted in an intramolecular aromatic substitution reaction by means of Ph₂P attack on the adjacent C₆F₅ ring to yield the zwitterionic phospha-indene derivative 7. The compounds 4a, 4c, 4d, and 7 were characterized by X-ray diffraction.