C−C Bond Formation of Mg‐ and Zn‐Activated Carbon Dioxide

• Published in: Chemistry : a European journal Vol. 24; no. 18; pp. 4710 - 4717
• Main Authors: Miller, Glenn B. S., Uggerud, Einar
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 26.03.2018
• Subjects: Acetaldehyde; Activated carbon; Atomic properties; Bonding; Carbohydrates; Carbon dioxide; Carbon dioxide fixation; Carbon sequestration; Chemistry; CO2 fixation; Coordination compounds; C−C bond formation; Electrochemistry; Energy of dissociation; Lactic acid; Magnesium; Mass spectrometry; Mass spectroscopy; Metals; Photosynthesis; Potential energy; Pyruvic acid; Quantum chemistry; Zinc; C−C bond formation; magnesium; mass spectrometry; CO2 fixation; zinc
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201706069

Gas‐phase activation of CO2 by chloride tagged metal atoms, [ClM]− (M=Mg, Zn), has been investigated by mass spectrometry and high‐level quantum chemistry. Both metals activate CO2 with significant bending of the CO2 moiety to form complexes with the general formula [ClM,CO2]−. The structure of the metal–CO2 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(κ2‐O2C)]− with acetaldehyde (here considered a carbohydrate mimic) was then studied. Formation of lactate and enolate‐pyruvate complexes are observed, showing that CO2 fixation by C−C bond formation takes place. For M=Zn, even formation of free pyruvate ([C3H3O3]−) is observed. Implications of the observed CO2 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. Activating CO2: Anionic chloride tagged complexes of magnesium and zinc, [ClM]− (M=Mg, Zn), can bind and activate CO2 to form complexes of the form [ClMCO2]−. It is demonstrated that complexes of this kind, [ClM(κ2‐O2C)]−, are carbon nucleophiles that can add to C=O bonds. Addition to CO2 results in carbonate and oxalate complexes, whereas addition to acetaldehyde results in lactate complexes and free pyruvate (see scheme).