Alkene complexes of ruthenium(0): crystal structures, isomerism and fluxionality

Abstract

The ligand arrangements in alkene complexes [Ru(CO)₂(alkene)LL′][alkene =E- or Z-MeO₂CCHCHCO₂Me, L = L′= PMe₂Ph or AsMe₂Ph, or L = PMe₂Ph, L′= P(OMe)₃; alkene = H₂CCH₂, H₂CCHCO₂Me, E-NCCHCHCN, Z-MeO₂CCHCClCO₂Me, or E- or Z-MeO₂CCHCPhCO₂Me, L = L′= PMe₂Ph] have been determined by IR and NMR spectroscopy and, in two instances, by X-ray crystallography. Three types of arrangement have been identified: their relative stabilities are discussed in terms of steric interactions between the alkene substituents and the ligands L and L′. Variable-temperature NMR studies on [Ru(CO)₂(E-MeO₂CCHCHCO₂Me)(PMe₂Ph)₂] have revealed that the complex is fluxional but that the fluxional motion is restricted by these same interactions. With Z-MeO₂CCHCHCO₂Me, complex formation is accompanied by alkene isomerisation: deuterium labelling experiments have thrown light on the mechanism of isomerisation.