Hydrogenation of carbon dioxide and aryl isocyanates by a tetranuclear tetrahydrido yttrium complex.: Isolation, structures, and CO2 insertion reactions of methylene diolate and μ3-oxo yttrium complexes

The reaction of carbon dioxide with a tetranuclear tetrahydrido yttrium complex [(C 5Me 4SiMe 3)Y(μ-H)] 4(L) (L = Me 3SiCC(H)C(H)CSiMe 3) (1) rapidly afforded the corresponding bis(methylene diolate) complex [(C 5Me 4SiMe 3)Y] 4(μ-O 2CH 2) 2(L) (2), while the reactions of an aryl isocyanate with 1 led to selective formation of the μ 3-oxo complex [(C 5Me 4SiMe 3)Y] 4(μ-O)( μ-H) 2(L) (5) or [(C 5Me 4SiMe 3)Y] 4(μ-O) 2(L) (7), depending on the substrate ratio. Both the methylene diolate and the oxo complexes can undergo CO 2 insertion reactions to give the corresponding carbonate complexes. These reactions not only yield a new series of polynuclear yttrium complexes having novel structures but also shed new light on the mechanistic aspects of the heterogeneous hydrogenation of CO 2. The high reactivity of the polynuclear μ 3-oxo yttrium complexes 5 and 7 could also make them novel molecular models for study of metal oxide-supported catalysts. Copyright © 2004 American Chemical Society.