Hydrogenation of Carbon Dioxide to Methanol Catalyzed by Iron, Cobalt, and Manganese Cyclopentadienone Complexes: Mechanistic Insights and Computational Design.

Density functional theory study of the hydrogenation of carbon dioxide to methanol catalyzed by iron, cobalt, and manganese cyclopentadienone complexes reveals a self-promoted mechanism, which features a methanol- or water-molecule-assisted proton transfer for the cleavage of H2 . The total free energy barrier of the formation of methanol from CO2 and H2 catalyzed by Knölker's iron cyclopentadienone complex, [2,5-(SiMe3 )2 -3,4-(CH2 )4 (η5 -C4 COH)]Fe(CO)2 H, is 26.0 kcal mol-1 in the methanol solvent. We also evaluated the catalytic activities of 8 other experimentally reported iron cyclopentadienone complexes and 37 iron, cobalt, and manganese cyclopentadienone complexes proposed in this study. In general, iron and manganese complexes have relatively higher catalytic activities. Among all calculated complexes, [2,5-(SiMe3 )2 -3,4-CH3 CHSCH2 (η5 -C4 COH)]Fe(CO)2 H (1Fe-Casey-S-CH3 ) is the most active one with a total free energy barrier of 25.1 kcal mol-1 in the methanol solvent. Such a low barrier indicates that 1Fe-Casey-S-CH3 is a very promising low-cost and high efficiency catalyst for the conversion of CO2 and H2 to methanol under mild conditions.