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

Abstract

Treatment of the bis(ethylene) complexes M(η6-arene)(η2-C2H4)2 (M = Ru, arene = C6Me6 (1); M = Os, arene = 1,3,5-C6H3Me3 (2)) with HPF6 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(CH2CH2-μ-H)(C2H4)(η-C6Me6)]+ 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(C2H4)2(η-C6H3Me3)]+ 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(C2H5)(C2H4)(L)(η-C6H3Me3)]PF6 (L = ButNC, P(OMe)3). Show more