Iron and Ruthenium Heterobimetallic Carbonyl Complexes as Electrocatalysts for Alcohol Oxidation: Electrochemical and Mechanistic Studies

Carbonyl-containing Ru and Fe heterobimetallic complexes were prepared and tested as electrocatalysts for the oxidation of methanol and ethanol. GC analysis of the electrolyte solution during bulk electrolysis indicated that CpRu(CO)(mu-I)(mu-dppm)PtI2 (1), CpFe(CO)(mu-I)(mu-dppm)-PtI2 (2), and CpRu(CO)(mu-I)(mu-dppm)PdI2 (3) were catalysts for the electrooxidation of methanol and ethanol, while CpFe(CO)(mu-I)(mu-dppm)-PdI2 (4), CpRu(CO)I(mu-dppm)AuI (5), and CpFe(CO)I(mu-dppm)AuI (6) did not function as catalysts. The oxidation of methanol resulted in two- and four-electron oxidation to formaldehyde and formic acid, respectively, followed by condensation with unreacted methanol to yield dimethoxymethane and methyl formate as the observed products. The oxidation of ethanol afforded 1,1'-diethoxyethane as a result of two-electron oxidation to acetaldehyde and condensation with excess ethanol. FTIR analysis of the headspace gases during the electrochemical oxidation of methanol indicated formation of CO2. Isotopic labeling experiments demonstrated that the CO2 resulted from oxidation of the CO ligand instead of complete oxidation of CH3OH.