Hydrogenation of biomass derivate catalysed by ruthenium (II) complexes containing phosphorus-nitrogen ligands under mild conditions

This work describes the synthesis and characterisation of Ru(II) complexes with the general formula RuCl₂(P,N)₂ (where P,N represents a heterobidentate P,N-donor chelated ligand) and their application as catalysts in furfural hydrogenation. The following precatalysts were synthetised: (dichloro bis-(N-(diphenylphosphino)pyridin-2-amine)ruthenium(II)) (RuL1), (dichloro bis-(N-(diphenylphosphino)pyrimidine-2-amine)ruthenium(II)) (RuL2), (dichloro bis-(2-((diphenylphosphino)methyl)pyridine)ruthenium(II))(RuL3), (dichloro bis-(2-((diphenylphosphino)ethyl)pyridine)ruthenium(II))(RuL4) and dichloro bis-(8-(diphenylphosphino)quinoline)ruthenium(II)) (RuL5). The major isomer in the synthesis of complexes RuL1 RuL2, RuL3 and RuL5, were cis-Cl, cis-N and cis-P configuration, only for the synthesis of complex RuL4 the major isomer was trans-Cl, trans-N, trans-Cl. All catalysts were active in the furfural hydrogenation; however, the RuL4 and RuL5 catalysts showed the best activity and selectivity in the proposed catalytic reaction, obtaining conversions of 88% and 97%, respectively, with a selectivity of 100% to furfuryl alcohol, using mild condition pressure (10 bar molecular hydrogen) and temperature (100 °C). The maximum turnovers were obtained with the catalysts RuL4 and RuL5 with values of 1760 h⁻¹(88% conversion) and 1940 h⁻¹(97% conversion), respectively, after only 30 mins. of reaction.