Ruthenium-Catalyzed Methanol Production from Aqueous Paraformaldehyde and Mechanistic Study

Abstract

A series of water-soluble arene-Ru(II) complexes, [(η⁶-p-cymene)RuCl(L)]⁺Cl^‒ ([Ru]-7 – [Ru]-12) (L = substituted bis-imidazole methane) exhibited efficient and selective methanol production from paraformaldehyde in water. The findings inferred a crucial role of the ligand in tuning the catalytic performance. A pH-dependent behavior of this series of catalysts was observed, where the amount of base was influential in methanol production from paraformaldehyde. The catalyst [Ru]-7 (L1 = 4,4′-((2-hydroxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole) was the most efficient among the explored catalysts giving a turnover number (TON) of 1200 at 90 °C. A mechanistic cycle has also been proposed for the catalytic reaction based on the mass and NMR investigations including those using deuterium-labelled molecules.