Synthesis, characterization and some catalytic properties of ruthenium complexes Ru(PPh(3))(2)Cl-2(L)(2) [L=4-Bu(t)-py, 4-vinyl-py,4-CN-py,4-Me-py,3-Me-py, L(2)=4,4'-bipy]. Kinetics of cyclohexene hydrogenation catalysed by Ru(PPh(3))(2)Cl-2(4-Bu(t)-py)(2)

The complexes Ru(PPh(3))(2)Cl-2(L)(2) (L =4-Bu(t)-py, 4-vinyl-py, 4-CN-py, 4-Me-py, 3-Me-py, L(2) = 4,4'-bipy) have been prepared by reaction of RUCl(2)(PPh(3))(3) with the appropriate ligand under mild conditions and characterized by elemental analysis, IR, NMR (H-1 and P-31) and UV-vis spectra; the Ru-II derivatives display a RuP2Cl2N2 core with a trans, cis, cis arrangement of the donor atoms. Ru(PPh(3))(2)Cl-2(4-Bu(t)-py)(2) is an efficient catalyst precursor for the homogeneous hydrogenation of cyclohexene and benzaldehyde under moderate conditions. A kinetic study of the hydrogenation of cyclohexene led to a rate law r = k(cat)[Ru][H-2], which corresponds to a mechanism involving a fast coordination of cyclohexene to an electronically unsaturated hydride RuHCl(PPh(3))(2)(4-Bu(t)-py), followed by a rate-limiting oxidative addition of H-2 and rapid reductive elimination of the product.