Stereoselectivity in a Chiral Ruthenium Ethylene Hydride Complex: Evidence of an Agostic Intermediate

Treatment of Ru(η6:η1-Me2NC6H4C6H4PCy2)Cl2 with MeLi resulted in the formation of Ru(η6:η1-Me2NC6H4C6H4PCy2)Me2, which reacted with Ph3CPF6 to form the cationic olefin hydride complex [Ru(η6:η1-Me2NC6H4C6H4PCy2)(H2CCH2)(H)]PF6. The new complexes were characterized by spectroscopy and by X-ray crystallographic analysis. The diastereomeric olefin hydride complexes were observed to exhibit two fluxional processes: a facile olefin rotation and another process that results in the exchange of the hydride and olefin protons. As the rate of diastereomer interconversion is much slower than that of olefin insertion, our studies suggest that the latter exchange takes place through an agostic species which undergoes dynamic methyl rotation.