Synthesis and characterization of [RuCl3(P-P)(H2O)] complexes; P-P = achiral or chiral, chelating ditertiary phosphine ligands

The reaction of the dinuclear [RuCl2(dppb)](2)(mu-dppb) (dppb = 1,4-bis(diphenylphosphino)butane) with Cl-2 in MeOH for similar to 30 min at room temperature gives the bright-red solid mer-RuCl3(dppb)(H2O) (1); Cl-2 treatment for similar to 10 min affords the red-brown, mixed valence complex [RuCl(dppb)](2)(mu-Cl)(3) (2). Controlled bulk coulometric reduction of 50% of the content of a CH2Cl2 solution of 1 also produces 2, formed by the reaction of 1 with "RuCl2(dppb)" produced in situ during the electrolysis. Complexes 1 and 2 were characterized by spectroscopic techniques [including electron spin resonance (ESR)], magnetic moments and cyclic voltammetry, and the structure of 1 was determined by X-ray diffraction. The structure shows that the aquo ligand forms hydrogen bonds with two cis-chlorine ligands of the neighboring molecule of the complex; this interaction gives rise to exchange coupling between two Ru(III) centers that is reflected in the ESR spectrum. A species 3 analogous to 1 has been obtained with the diop ligand [diop = (2R,3R)- or (2S,3S)-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] , on using RuCl2(diop)(PPh3) or [RuCl(diop)](2)(mu-Cl)(3) as precursors. The RuCl3(P-P)L complexes (P-P = dppb, diop; L = dimethyl sulfoxide, MeOH) are readily synthesized from 1 or 3.