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(L1–L3)(X)(EPh3)2] (where L1–L3 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, d5) 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 (gx ≠ gy ≠ gz) 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.

Graphical abstractRuthenium(III) complexes of general formula [Ru(L1–L3)(X)(EPh3)2] (where X = Cl (or) Br; E = P or As, L1–L3 are dianionic tridentate chelator) have been synthesized and characterized by analytical and spectral methods. The catalytic activity of one of the complexes [Ru(pcr-chx)Br(AsPh3)2] (7) was examined in the transfer hydrogenation of ketones and was found to be an efficient catalyst with conversion up to 99% in the presence of isopropanol/KOH.Figure optionsDownload full-size imageDownload as PowerPoint slide