Kinetic study of the hydrosilylation of acetophenone by [Rh(cod)Cl]2/(R)-BINAP

The [Rh(cod)Cl](2)/(R)-BINAP catalyzed hydrosilylation reaction between acetophenone and H2SiPh2, H2SiEt2, H2SiBu2, HSiBu3, HSiPh3, and HSi(p-F3CC6H4)(3) in benzene-d(6) at 63degreesC has been studied by H-1 NMR spectroscopy, GC/MS, and H/D exchange experiments with acetophenone-d(6), The reactions afford varying amounts of PhCH(OSiZ(3))Me (3), PhC(OSiZ(3))= CH2 (4), and PhCH(OH)Me (5). The product distribution of the reaction is dependent on the order of mixing for the secondary silanes but independent of the order of mixing for tertiary silanes. The product distributions and initial rates of reaction of the tertiary silanes, which react more slowly than the secondary silanes, are dependent on the stereoclectronic properties of the silane, with HSi(p-F3CC6H4)(3) being 10 times more reactive than HSiPh3. The reaction involving HSiBu3 is first order in the initial concentration of [Rh(cod)Cl](2)/(R)-BINAP as well as the concentration of HSiBu3 but shows a saturation effect at high concentrations of acetophenone. In the earliest phases of the reaction, the coordinated cyclooctadiene is liberated and converted to cyclooctane and cyclooctene. The requisite hydrogens for the hydrogenation process come mainly from HSiBu3. The products 4 and 5 appear to be formed independently of the formation of 3. The catalysts for the formation of 4 and 5 appeared to decay, thereby abruptly terminating the formation of these materials after about 40% of the acetophenone had been consumed. Simulation of the kinetic results, based on the Ojima mechanism, qualitatively fits the production of 3.