Reduction of CO2 by Pyridine Monoimine Molybdenum Carbonyl Complexes: Cooperative Metal-Ligand Binding of CO2

• Published in: Chemistry : a European journal 2015-06, Vol.21 (23), p.8497-8503
• Main Authors: Sieh, Daniel, Lacy, David C., Peters, Jonas C., Kubiak, Clifford P.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbonyl compounds; Chemical reduction; Chemistry; CO2 reduction; Electrochemistry; Ligands; Molybdenum; redox-active ligands; spectroelectrochemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500463

[(ArPMI)Mo(CO)4] complexes (PMI=pyridine monoimine; Ar=Ph, 2,6‐di‐iso‐propylphenyl) were synthesized and their electrochemical properties were probed with cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC). The complexes undergo a reduction at more positive potentials than the related [(bipyridine)Mo(CO)4] complex, which is ligand based according to IR‐SEC and DFT data. To probe the reaction product in more detail, stoichiometric chemical reduction and subsequent treatment with CO2 resulted in the formation of a new product that is assigned as a ligand‐bound carboxylate, [( iPr 2PhPMI)Mo(CO)3(CO2)]2−, by NMR spectroscopic methods. The CO2 adduct [( iPr 2PhPMI)Mo(CO)3(CO2)]2− could not be isolated and fully characterized. However, the CC coupling between the CO2 molecule and the PDI ligand was confirmed by X‐ray crystallographic characterization of one of the decomposition products of [( iPr 2PhPMI)Mo(CO)3(CO2)]2−. Molybdenum pyridine monoimine tetracarbonyl complexes were synthesized and fully characterized. They were tested for electrocatalytic carbon dioxide reduction, but no catalytic turnover was observed. From reactions of the chemically reduced complexes with CO2, the CO2 carbon atom was shown to bind to the ligand backbone of the pyridine monoimine ligand.