Insertion of Carbon Dioxide into Mg−N Bonds. Structural Characterization of a Previously Unknown η2 Chelation Mode to Magnesium in Magnesium Carbamates

Insertion reactions of CO2 into magnesium amides that yield carbamates are known, and several different bonding modes of the −O2CNR2 moiety to magnesium have been previously identified. However, conspicuous by its absence is the simplest mode of chelation of the carbamate to a single Mg atom, the η2 chelating mode. We have now discovered that the insertion of CO2 into Mg2(NCy2)4 (Cy = cyclohexyl) in THF/HMPA (HMPA = hexamethylphosphoramide) forms the unsymmetrical dinuclear compound [Mg2(O2CNCy2)4(HMPA)] (1). X-ray diffraction analysis shows that 1 contains three different bonding modes of the carbamate to the Mg atoms, including the first example of the terminal bidentate η2 mode.