Development of Effective Bidentate Diphosphine Ligands of Ruthenium Catalysts toward Practical Hydrogenation of Carboxylic Acids

Hydrogenation of carboxylic acids (CAs) to alcohols represents one of the most ideal reduction methods for utilizing abundant CAs as alternative carbon and energy sources. However, systematic studies on the effects of metal-to-ligand relationships on the catalytic activity of metal complex catalysts are scarce. We previously demonstrated a rational methodology for CA hydrogenation, in which CA-derived cationic metal carboxylate [(PP)M(OCOR)](+) (M = Ru and Re; P = one P coordination) served as the catalyst prototype for CA self-induced CA hydrogenation. Herein, we report systematic trial-and-error studies on how we could achieve higher catalytic activity by modifying the structure of bidentate diphosphine (PP) ligands of molecular Ru catalysts. Carbon chains connecting two P atoms as well as Ar groups substituted on the P atoms of PP ligands were intensively varied, and the induction of active Ru catalysts from precatalyst Ru(acac)(3) was surveyed extensively. As a result, the activity and durability of the (PP)Ru catalyst substantially increased compared to those of other molecular Ru catalyst systems, including our original Ru catalysts. The results validate our approach for improving the catalyst performance, which would benefit further advancement of CA self-induced CA hydrogenation.

Automated summary

The study focused on modifying the structure of bidentate diphosphine (PP) ligands to achieve higher catalytic activity in carboxylic acid hydrogenation, leading to significantly increased activity and durability of the (PP)Ru catalyst compared to other molecular Ru catalyst systems. The approach used in this study could benefit further advancements in carboxylic acid self-induced hydrogenation.