Homobimetallic Ruthenium-Arene Complexes Bearing Vinylidene Ligands Synthesis, Characterization, and Catalytic Application in Olefin Metathesis

Five new arylvinylidene complexes with substituents ranging from electron-donating to strongly withdrawing (p-OMe, p-Me, p-Cl, p-CF3, and m-(CF3)2) were isolated in high yields by reacting [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(PCy3)] (3) with the corresponding phenylacetylene derivatives. The known phenylvinylidene complex [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(PCy3)] (5) was also obtained from [RuCl2(p-cymene)]2, tricyclohexylphosphine, and phenylacetylene under microwave irradiation. The influence of the remote aryl substituents on structural features was investigated by IR, NMR, and XRD spectroscopies. A very good linear relationship was observed between the chemical shift of the vinylidene α-carbon atom and the Hammett σ-constants of the aryl group substituents. The catalytic activity of the six homobimetallic complexes was probed in various types of olefin metathesis reactions. Unsubstituted phenylvinylidene compound 5 served as a lead structure for these experiments. Its reaction with norbornene afforded hig...