Dual utility of a single diphosphine-ruthenium complex: a precursor for new complexes and, a pre-catalyst for transfer-hydrogenation and Oppenauer oxidation.

The diphosphine-ruthenium complex, [Ru(dppbz)(CO) 2 Cl 2 ] (dppbz = 1,2-bis(diphenylphosphino)benzene), where the two carbonyls are mutually cis and the two chlorides are trans , has been found to serve as an efficient precursor for the synthesis of new complexes. In [Ru(dppbz)(CO) 2 Cl 2 ] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl 2 ] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO) 2 Cl 2 ] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz) 2 Cl 2 ]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO) 2 Cl 2 ] could be displaced together by chelating mono-anionic bidentate ligands, viz. anions derived from 8-hydroxyquinoline (Hq) and 2-picolinic acid (Hpic) via loss of a proton, to afford the mixed-tris complexes [Ru(dppbz)(q) 2 ] and [Ru(dppbz)(pic) 2 ], respectively. The molecular structures of four selected complexes, viz. [Ru(dppbz)(CO)(dmso)Cl 2 ], [Ru(dppbz) 2 Cl 2 ], [Ru(dppbz)(q) 2 ] and [Ru(dppbz)(pic) 2 ], have been determined by X-ray crystallography. In dichloromethane solution, all the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the complexes shows redox responses within 0.71 to -1.24 V vs. SCE. [Ru(dppbz)(CO) 2 Cl 2 ] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.