Titanocene(III) catalyzed homogeneous hydrosilation-hydrogenation of pyridines

The homogeneous catalytic hydrosilation-hydrogenation of pyridines is obser ved in the presence of Cp2TiMe2 (Cp = eta (5)-C5H5) and CpCp*TiMe2 (Cp* = e ta (5)-C5Me5) as catalysts and using PhSiH3 or PhMeSiH2 as the source of Si -H. Under appropriate conditions, and with appropriate ring-substitution, g ood yields of the N-silyl-dihydropyridine or N-silyltetrahydropyridine prod ucts are be obtained. Although complete saturation is not achieved with org anosilane alone, carrying out the reaction under moderate H-2 pressures can give excellent yields of N-silylpiperidines. Under moderate pressures of H -2, [Cp2TiH](2) catalyzes rapid H-D exchange between H-2 and the 2- and 6-p ositions of C5D5N. Under the same conditions, only traces of hydrogenation are observed. This, together with the regioselectivity of 3-picoline hydros ilation-hydrogenation, leads to the conclusion that the key step in the rea ction is probably addition of Ti-Si to C=N.