Hydrogenation of Carbon Dioxide and Aryl Isocyanates by a Tetranuclear Tetrahydrido Yttrium Complex. Isolation, Structures, and CO<sub>2</sub> Insertion Reactions of Methylene Diolate and μ<sub>3</sub>-Oxo Yttrium Complexes
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The reaction of carbon dioxide with a tetranuclear tetrahydrido yttrium complex [(C5Me4SiMe3)Y(μ-H)]4(L) (L = Me3SiCC(H)C(H)CSiMe3) (1) rapidly afforded the corresponding bis(methylene diolate) complex [(C5Me4SiMe3)Y]4(μ-O2CH2)2(L) (2), while the reactions of an aryl isocyanate with 1 led to selective formation of the μ3-oxo complex [(C5Me4SiMe3)Y]4(μ-O)( μ-H)2(L) (5) or [(C5Me4SiMe3)Y]4(μ-O)2(L) (7), depending on the substrate ratio. Both the methylene diolate and the oxo complexes can undergo CO2 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 CΟ2. The high reactivity of the polynuclear μ3-oxo yttrium complexes 5 and 7 could also make them novel molecular models for study of metal oxide-supported catalysts.
