The thermal catalytic hydrosilylation of 1,3-butadiene (1), trans-2-methyl-1, 3-pentadiene (2), 2,3-dimethyl-1,3-butadiene (3), and isoprene (4), with triethylsilane were studied in the presence of M(CO)(3) (o-xylene) (M = Cr, Mo, W) complexes in polar and nonpolar solvents such as tetrahydrofuran, hexane and toluene. Mo(CO)(3) (o-xylene) was found to be the only active catalyst for the hydrosilylation of 3 with triethylsilane, which gave 1-triethylsilyl-2,3-dimethyl-2-butene (3a), as hydrosilylated product in tetrahydrofuran. The product was identified by means of H-1 and C-13-NMR and GLC. The same catalyst, Mo(CO)(3) (o-xylene), decomposed to MO(CO)(6) without giving hydrosilylated products of 1, 2 and 4 in tetrahydrofuran. M(CO)(3) (o-xylene) (M = Cr, Mo, W) complexes were found to be stable for about 6 h in hexane and toluene, and showed no catalytic activity for the hydrosilylation of 1, 2, 3 and 4.