Rational synthesis of ruthenium-based metallo-supramolecular polymers as heterogeneous catalysts for catalytic transfer hydrogenation of carbonyl compounds

Abstract

Ruthenium-based metallo-supramolecular polymers (Ru-MSPs) were synthesized by complexing Ru ions with 1,4-bis(1,10-phenanthrolin-5-yl)benzene ligands for heterogeneously catalytic transfer hydrogenation of carbonyl compounds with formate. The degree of polymerization and the local environment of Ru atoms in Ru-MSP were tailored by tuning the ligand/metal ratio and the synthesis temperature/period. The coordinatively-unsaturated Ru atoms are identified as the active centers in Ru-MSP for carbonyl reduction. Ru-MSP is much more active than Ru-based counterparts including its monomeric analogue, which is attributed to (1) the higher electron density in Ru atoms that facilitates the selective dehydrogenation of formate via C-H dissociation, and (2) the lower LUMO of ligand moieties that activates the carbonyl oxygen via Lewis acid-base interactions. Furthermore, Ru-MSP displays high reusability and capability of catalyzing a wide scope of carbonyl compounds. These findings demonstrate that the rationally-designed polymerization is a promising approach to heterogenize the catalytically active metal complexes with enhanced performance.