Synthesis, characterization and reactivity of halides/pseudohalides and their complexes containing ruthenium II in the hydrogenation of cyclohexene

Abstract

In this paper, the influence of pseudohalide ligands coordinated to the ruthenium center on the hydrogenation of cyclohexene was investigated. The pseudohalide complexes containing ruthenium were synthesized from the cis-[RuCl2(dppb)(N-N)] {where N-N=2,2′-bipyridine (bipy) (1A), 4,4′-dimethyl-2,2′-bipyridine (Me-bipy) (2), or 4,4′-dimethoxy-2,2′-bipyridine (MeO-bipy) (3), dppb=1,4-bis(diphenylphosphino)butane}, by chloride exchange to provide complexes with general formula cis-[RuL2(dppb)(N-N)] {where L2=N3−(4), (7) and (9) CN−(5), (8) and (10) or SCN−(6) and (11)}. All complexes were characterized using spectroscopic, electrochemical techniques, as well as elemental analyses to check their molecular formulation and purity. Furthermore, crystal structure of the complexes cis-[Ru(N3)2(dppb)(bipy)] (4), cis-[Ru(CN)2(dppb)(bipy)] (5), cis-[Ru(SCN)2(dppb)(bipy)] (6), cis-[Ru(CN)2(dppb)(Me-bipy)] (8), and cis-[Ru(SCN)2(dppb)(MeO-bipy)] (11) were determined by single-crystal X-ray diffraction, as well as the X-ray structure of the solvate complex [RuCl(CH3CN)(dppb)(bipy)](PF6) (1B). Dichloride and pseudohalide complexes containing ruthenium were applied as pre-catalysts in the hydrogenation of cyclohexene, after pre-established conditions using the cis-[RuCl2(dppb)(bipy)] (1A) as a target complex. The quantitative conversion of cyclohexene to cyclohexane was obtained in 5h at 25°C using 0.1mol% of (1A) in methanol solution at 15atm H2. The substituted bipy derivatives (2) and (3) were also effective pre-catalysts, but pseudohalides were not under these conditions.