Deoxygenative Coupling of CO with a Tetrametallic Magnesium Hydride Complex.

Addition of CO to a tetrametallic magnesium hydride cluster results in both carbon-carbon bond formation and deoxygenation to generate an acetaldehyde enolate [COH] which remains coordinated to the cluster. To the best of our knowledge, this is the first example of formation of an isolable complex containing an [COH] fragment from reaction of CO with a metal hydride, and the first example of CO homologation and deoxygenation at a main group metal. DFT studies suggest that key steps in the mechanism involve nucleophilic attack of an oxymethylene on a formyl ligand to generate an unstable [COH] fragment, which undergoes subsequent deoxygenation.