Ligand Modification-Induced Electronic Effects and Synergistic Protic Solvent Effects Promote C═O Bond Hydrogenation

Catalytic hydrogenation conducted on heterogeneous catalysts usually proceeds via the Horiuti-Polanyi mechanism. Despite the feasibility of homolytically dissociated hydrogen species on metal surfaces for the hydrogenation of nonpolar bonds, sluggish hydrogenation of ketones and aldehydes is observed under mild conditions due to the mismatched electronic features of H atoms on the metal surfaces and the polar C═O bonds. Here, we employed well-defined model catalysts to demonstrate that ligand-modified Pd surfaces exhibit significantly higher activity for the hydrogenation of polar unsaturated C═O bonds compared to clean Pd surfaces. Detailed experimental analysis and DFT calculations revealed that ligand-induced interfacial electronic effects facilitate the nucleophilic addition of hydride to the C+ site in the C═O bond. Simultaneously, the transfer of the proton in the protic solvent to the O site promotes overall hydrogenation. The rational design and utilization of hydrogen species with different electronic properties disrupt the linear scaling relationship involved in stepwise hydrogenation on metal surfaces, thereby significantly boosting the catalytic hydrogenation of C═O bonds under mild conditions.