C-C Bond Formation of Mg- and Zn-Activated Carbon Dioxide.

Gas-phase activation of CO by chloride tagged metal atoms, [ClM] (M=Mg, Zn), has been investigated by mass spectrometry and high-level quantum chemistry. Both metals activate CO with significant bending of the CO moiety to form complexes with the general formula [ClM,CO ] . The structure of the metal-CO complex depends on the method of formation, and the energy landscapes and reaction dynamics have been probed by collisional induced dissociation and thermal ion molecule reactions with isotopically labeled species. Having established these structural relationships, the gas-phase reactivity of [ClM(κ -O C)] with acetaldehyde (here considered a carbohydrate mimic) was then studied. Formation of lactate and enolate-pyruvate complexes are observed, showing that CO fixation by C-C bond formation takes place. For M=Zn, even formation of free pyruvate ([C H O ] ) is observed. Implications of the observed CO reactivity for the electrochemical conversion of carbon dioxide, and to biochemical and artificial photosynthesis is briefly discussed. Detailed potential energy diagrams obtained by the quantum chemical calculations offer models consistent with experimental observation.