Insertion of Carbon Dioxide into Mg−N Bonds. Structural Characterization of a Previously Unknown η<sup>2</sup> Chelation Mode to Magnesium in Magnesium Carbamates

Insertion reactions of CO<sub>2</sub> into magnesium amides that yield carbamates are known, and several different bonding modes of the −O<sub>2</sub>CNR<sub>2</sub> 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 η<sup>2</sup> chelating mode. We have now discovered that the insertion of CO<sub>2</sub> into Mg<sub>2</sub>(NCy<sub>2</sub>)<sub>4</sub> (Cy = cyclohexyl) in THF/HMPA (HMPA = hexamethylphosphoramide) forms the unsymmetrical dinuclear compound [Mg<sub>2</sub>(O<sub>2</sub>CNCy<sub>2</sub>)<sub>4</sub>(HMPA)] (<b>1</b>). X-ray diffraction analysis shows that <b>1</b> contains three different bonding modes of the carbamate to the Mg atoms, including the first example of the terminal bidentate η<sup>2</sup> mode.