Mechanistic Study and Ligand Design for the Formation of Zinc Formate Complexes from Zinc Hydride Complexes and Carbon Dioxide

Density functional theory (DFT) study of the reactions of mononuclear phenolate diamine zinc hydride complexes and CO₂ reveals a direct insertion mechanism with a rate-determining C–H bond formation step. A total of 16 zinc hydride complexes with various functional groups, including 3 experimental structures and 13 newly proposed complexes, have been optimized. The influences of various substituents at different positions, the ring size of nitrogen bidentate ligands, and the ortho groups of nitrogen on the reaction rate are investigated. Computational results indicate that the ortho effect of nitrogen is the most effective factor in reducing the reaction energy barrier, and the complex with isopropyls as the ortho groups of the nitrogen atom has the lowest barrier of 10.9 kcal/mol.