Kinetic study of iridium(I) complexes as homogeneous hydrogenation catalysts

Abstract

A study is described of the kinetics of reactions in which the complexes trans-IrX(CO)(PPh3)2, where X = Cl, Br, and I, are used for the catalytic homogeneous hydrogenation of olefinic bonds. Catalytic activity is enhanced in coordinating solvents such as dimethylacetamide. The rate law is complex, showing between zero and first order in each of iridium, substrate, and hydrogen concentrations, and the mechanisms proposed show the importance of a dissociation step in making available a coordination site on the transition metal complex. The dependence of rate on the halogen followed the order I > Br > Cl. Quite remarkably, traces of oxygen in the system enhance the hydrogenation rate considerably.