Ruthenium(0) Catalyzed Isomerization of Allylbenzene. The Detection and Isolation of A Hydrido-η3-Allyl Intermediate

Abstract

Allylbenzene is isomerized to cis- and trans-β-methylstyrene at 35–60°C in the presence of [(C6H5)3P]4Ru(π-CH3CN)·CH3CN. Two hydrido-η3-1-phenylallyl ruthenium complexes have been detected by proton nmr spectroscopy during the reaction and the predominant one of formula [(C6H5)3P]2RuH(η3-C3H4C6H5)(CH3CN) has been isolated. The structure of this intermediate contains cis phosphines, mutually trans hydrido and acetonitrile ligands and the 1-phenylallyl ligand in a syn-configuration. A similar structure with an anti-configuration of the 1-phenylallyl ligand is suggested for the other detected intermediate. These complexes indicate that this isomerization is initiated by oxidative-addition of ruthenium(0) to an allylic C-H bond with the formation of distinct η3-allyl metal hydride species as has been proposed in a number of metal catalyzed olefin transformations.