Carbon dioxide into metal-alkoxide bonds

The insertion of carbon dioxide into a transition metal-oxygen bond, e.g., a metal alkoxide, results in an organic carbonate ester, coordinated in either a monodentate or bidentate manner. Only a limited number of such reactions have been observed, and little mechanistic information is available. The reactions may proceed by interaction of C02 with ROH or RO in solution followed by metal coordination, in a manner similar to the C02 reactions with the early transition metal dialkylamides. Alternatively, direct attack of C02 on the alkoxide oxygen might occur, or a C02 adduct may form as an intermediate. 

Basic ionic metal oxides or hydroxides such as CaO or KOH absorb CO2 to give metallic carbonates. Many covalent organometallic oxides or alkoxides similarly undergo insertion of carbon dioxide into the metal-oxygen bond to give the corresponding metal carbonates or alkyl metal carbonates ... 

Carbon dioxide also can undergo insertion into metal—heteroatom bonds. The following shows the reversible reaction with alkoxides - ... 

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