ALKENE COMPLEXES OF RUTHENIUM(O) - CRYSTAL-STRUCTURES, ISOMERISM AND FLUXIONALITY

The ligand arrangements in alkene complexes (Ru(CO)2(alkene)LL'] (alke ne = E- or Z-MeO2CCH = CHCO2Me, L = L' = PMe2Ph or AsMe2Ph, or L = PMe 2Ph, L' = P(OMe)3; alkene = H2C = CH2, H2C = CHCO2Me, E-NCCH = CHCN, Z -MeO2CCH = CClCO2Me, or E- or Z-MeO2CCH = CPhCO2Me, L = L' = PMe2Ph] h ave been determined by IR and NMR spectroscopy and, in two instances, by X-ray crystallography. Three types of arrangement have been identif ied: their relative stabilities are discussed in terms of steric inter actions between the alkene substituents and the ligands L and L'. Vari able-temperature NMR studies on [Ru(CO)2(E-MeO2CCH = CHCO2Me)(PMe2Ph)2 ] have revealed that the complex is fluxional but that the fluxional m otion is restricted by these same interactions. With Z-MeO2CCH=CHCO2Me , complex formation is accompanied by alkene isomerisation: deuterium labelling experiments have thrown light on the mechanism of isomerisat ion.