Reduction of Transition-Metal-Coordinated Carbon Monoxide by a Rare-Earth Hydride Cluster: Isolation of Well-Defined Heteromultimetallic Oxycarbene, Oxymethyl, Carbene, and Methyl Complexes

摘要

The reduction of coordinated carbon monoxide (CO) in transition-metal carbonyl complexes by metal hydrides is of critical importance, not only for mechanistic aspects of the Fischer-Tropsch synthesis, which involves the hydrogena-tion of CO in the presence of transition-metal catalysts, but also because of its potential applications in the development of homogeneous catalytic systems for the selective formation of hydrocarbons and oxygenates. To date, extensive studies have been carried out on the hydrogenation of coordinated CO by main-group-metal hydride reagents (e.g., LiAlH4 and NaBH4) or transition-metal hydride complexes, for example [Cp*2ZrHX] (Cp* = C5Me5; X = H, halide), The formation of various products (or intermediates) such as formyl (M- CHO), oxycarbene (M=CHOM), enediolate (MOCH= CHOM), oxymethyl (MCH2OM), and methyl (M-Me or M-CH2-M) species has been observed, but only a limited number of these compounds has been structurally characterized. In contrast, the reduction of coordinated CO by rare-earth (Group 3 and lanthanide) metal hydrides has hardly been studied. The only precedent was the reaction of scandocene hydride complex [Cp*2ScH(thf)] with [CpCo(CO)2] (Cp = C5H5), which yielded the scandoxycarbene species [CpCo(-CO)C(H)OScCp*2].