Homogeneous hydrogenation of 1-hexene by ruthenium(II) carbonyl phosphine complexes of the types (R3P)2Ru(CO)2Cl2 and (R3P)3Ru(CO)Cl2: effects of the nature of the phosphine, of complex geometry and stoichiometry on catalytic efficiency

Article abstract of DOI:10.1016/0022-328X(88)80677-6

A series of ruthenium(II) complexes of the types (R3P)2Ru(CO)2Cl2 (R3P=BzlP, Ph3P, Ph2MeP, PhMe2P and Me3P) and (R3P)3Ru(CO)Cl2 (R3P=Ph2MeP, PhMe2P and Me3P) were investigated for their ability to catalyze the homogeneous hydrogenation of 1-hexene at 100 deg C and a hydrogen pressure of 100 psi in 50percent ethanol/benzene.Each of the complexes catalyzed both the hydrogenation of 1-hexene to hexane and its isomerization to 2- and 3-hexenes, probably by a monohydride pathway.Both the geometry and stoichiometry of the complex effect the rates of hydrogenation and isomerization.For both series of complexes, the catalytic rate decreases with a decrease in the size and an increase in the basicity of the phosphine.For the (R3P)2Ru(CO)2Cl2 complexes, the ttt isomers were more active than the cct isomers.However, for the (R3P)3Ru(CO)Cl2 complexes, the complex geometry did not influence the catalytic activity.Hydrogenation reactions using ttt-(Ph2MeP)2Ru(CO)2Cl2 were carried out in the presence of the Lewis acids: AlCl3, BCl3 and SnCl2*H2O as well as with Me3NO.Both BCl3 and AlCl3 completly infibited hydrogenation and reduced the rate of hexene isomerization.SnCl2*2H2O slowed the rate of hydrogenation but had little effect on isomerization.Me3NO had little effect on hydrogenation but significantly increased the rate of hexene isomerization.The ruthenium species present at the termination of the catalysis experiments were characterized by infrared and NMR spectroscopy.In most cases the thermodynamically stable isomer of these complexes was recovered in high yield.