Ruthenium(III) complexes of amine-bis(phenolate) ligands as catalysts for transfer hydrogenation of ketones

Twelve ruthenium(III) complexes bearing amine-bis(phenolate) tripodal ligands of general formula [Ru(L-1-L-3)(X)(EPh3)(2)] (where L-1-L-3 are dianionic tridentate chelator) have been synthesized by the reaction of ruthenium(III) precursors [RuX3(EPh3)(3)] (where E = P, X = Cl; E = As, X = Cl or Br) and [RuBr3(PPh3)(2)(CH3OH)] with the tripodal tridentate ligands H2L1, H2L2 and H2L3 in benzene in 1:1 molar ratio. The newly synthesized complexes have been characterized by analytical (elemental and magnetic susceptibility) and spectral methods. The complexes are one electron paramagnetic (low-spin, d(5)) in nature. The EPR spectra of the powdered samples at RT and the liquid samples at LNT shows the presence of three different 'g' values (g(x) not equal g(y) not equal g(z)) indicate a rhombic distortion around the ruthenium ion. The redox potentials indicate that all the complexes undergo one electron transfer process. The catalytic activity of one of the complexes [Ru(pcr-chx)Br(AsPh3)(2)] was examined in the transfer hydrogenation of ketones and was found to be efficient with conversion up to 99% in the presence of isopropanol/KOH. (c) 2007 Elsevier Ltd. All rights reserved.