The protonation of arene-bis(ethylene) complexes of ruthenium and osmium

Abstract

Treatment of the bis(ethylene) complexes M(η 6-arene)(η 2-C 2H 4) 2 (M = Ru, arene = C 6Me 6 ( 1); M = Os, arene = 1,3,5-C 6H 3Me 3 ( 2)) with HPF 6 gives isolable monoprotonated salts 3 and 4. Variable temperature 1H and 13C NMR spectra show that the ruthenium compound 3 contains a β-agostic ethyl(ethylene) cation [ Ru(CH 2CH 2-μ-H )(C 2H 4)(η-C 6Me 6)] + in which the bridging hydrogen atom migrates rapidly between the ethyl group and coordinated ethylene, even at −100°C. This process, combined with rotation of the ethylene ligand, causes all nine hydrogen atoms to become equivalent at high temperature. The osmium salt 4 contains a hydridobis(ethylene) cation [OsH(C 2H 4) 2(η-C 6H 3Me 3)] + in which the ethylene ligands rotate rapidly about the metal-olefin axis even at −100°C. Migration of the hydride ligand between the metal atom and the ethylene ligands in 4 is slow on the NMR time scale at room temperature; the presumed intermediate ethyl derivative can be trapped by addition of ligands (L) to give stable salts [Os(C 2H 5)(C 2H 4)(L)(η-C 6H 3Me 3)]PF 6 (L = Bu tNC, P(OMe) 3).