Preparation, mechanism of formation, structure, and reactions of η-allyl complexes of ruthenium(II)

Abstract

Reaction of either of two isomers of [Ru(CO)₂Cl₂(PMe₂Ph)₂] or either of two isomers of [{Ru(CO)Cl₂(PMe₂Ph)₂}₂] with SnBu₃(C₃H₅) yields a single isomer of [Ru(CO)Cl(η-C₃H₅)(PMe₂Ph)₂]. A mechanism involving the intermediate formation of the five-co-ordinate species [Ru(CO)Cl₂(PMe₂Ph)₂] and [Ru(CO)Cl(σ-C₃H₅)(PMe₂Ph)₂] is proposed for the reactions. Treatment of complexes [{Ru(Co)₂Cl₂L}₂](L = phosphorus or arsenic ligand) with SnBu₃(C₃H₅) yields the related complexes [Ru(CO)₂Cl(η-C₃H₅)L], and the method can be extended to the preparation of 1-methylallyl and 2-methylallyl complexes. Simulation of the complex ¹H n.m.r. spectra of [Ru(CO)₂Cl(η-C₃H₅)(PMe₂Ph)] and its AsMe₂Ph analogue provides detailed information about the coupling between the protons in the allyl ligand. Treatment of [Ru(CO)₂Cl(η-C₃H₅)(PMe₂Ph)] with excess of PMe₂Ph results in the formation of [Ru(CO)Cl(COC₃H₅)(PMe₂Ph)₃], which is very slowly converted in solution into [Ru(CO)Cl(η-C₃H₅)(PMe₂Ph)₂]: the key intermediate in the system appears to be [Ru(CO)₂Cl(σ-C₃H₅)(PMe₂Ph)₂].