Synthesis and Properties of Silylene Cobalt(III) Hydrides

Three hexa‐coordinate bis(silylene) cobalt(III) hydrides, (RC( t BuN) 2 (Cl)Si) 2 Co(PMe 3 )(SiH 2 Ph)(H)(Cl)) (R = p ‐MeC 6 H 4 ( 4 ), p ‐ t BuC 6 H 4 ( 5 ) and 3,5‐Me 2 C 6 H 3 ( 6 )), bearing different substituents on the silylene ligand benzene rings, were synthesized via reactions of the penta‐coordinate bis(silylene) cobalt(I) chlorides (RC( t BuN) 2 (Cl)Si) 2 Co(PMe 3 ) 2 (Cl)) (R = p ‐MeC 6 H 4 ( 1 ), p ‐ t BuC 6 H 4 ( 2 ) and 3,5‐Me 2 C 6 H 3 ( 3 )) with PhSiH 3 in diethyl ether. Additionally, the hexa‐coordinate mono(silylene) cobalt(III) hydride (RC( t BuN) 2 (Cl)Si)Co(PMe 3 ) 2 (SiH 2 Ph)(H)(Cl)) (R = 3,5‐Me 2 C 6 H 3 ) ( 7 ) was obtained from the reaction of complex 3 with PhSiH 3 in n ‐pentane. Complexes 4–7 demonstrated good catalytic activity and selectivity in the hydrosilylation of 1‐heptene and Ph 2 SiH 2 , affording the anti ‐Markovnikov product, heptyldiphenylsilane, as the major product. The introduction of alkyl groups on the silylene ligand benzene rings was found to reduce the catalytic activity of cobalt(III) hydrides 4–7 , while the anti ‐Markovnikov selectivity remained largely unaffected. This decrease in activity may be attributed to enhanced complex stability imparted by the electron‐donating alkyl groups. The molecular structures of complexes 4–7 were unequivocally determined by single crystal X‐ray diffraction analysis.