Synthesis of new ruthenium complexes and their use as catalysts in the hydrogenation of diene compounds

Abstract

Ruthenium half-sandwich complexes [Cp*Ru (diene compound)]⁺X⁻ containing various commercially available diene compounds as ligands were tested as catalysts for the hydrogenation of diene compounds. Complexes containing acyclic, cyclic, bicyclic dienes, and α,β-unsaturated carboxylic acids and their derivatives as diene ligands were successfully prepared. The anionic part of the complexes (X⁻) was represented by triflate, perchlorate and tetrafluoroborate ions. Hydrogenations were carried out in homogeneous and heterogeneous arrangements. The desired products with Z-configuration of the double bond were formed with high selectivity (95–99%) in both cases. It was found out that selectivity was influenced neither by the type of diene ligand nor by the type of the anionic part of the complex. The hydrogenation rate was influenced by the type and the size of the diene ligand. The rate of hydrogenation of diene using complexes containing isolated cyclic or bicyclic ligands was the highest. The lowest reaction rates were observed using complexes with acyclic dienes. The influence of the type of the anionic part of the complex on the reaction rate was also studied. The lowest rate of hydrogenation was observed using complexes with tetrafluoroborate anion. The difference in reaction rates using complexes with triflate and perchlorate anions was not significant. This work added important information for the understanding the mechanism of diene hydrogenation using ruthenium half-sandwich complexes.