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

Abstract

The diphosphine–ruthenium complex, [Ru(dppbz)(CO)₂Cl₂] (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)₂Cl₂] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl₂] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO)₂Cl₂] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz)₂Cl₂]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO)₂Cl₂] 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)Cl₂], [Ru(dppbz)₂Cl₂], [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)₂Cl₂] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.