Chemistry of ruthenium in N(2)P(2)X(2) (X=Cl, Br) coordination sphere: Synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh(3))(3)X(2)] (X = Cl, Br) in dichloromethane solution affords [Ru(PPh(3))(2)(pap)X(2)]. These diamagnetic complexes exhibit a weak d-d transition and two intense MLCT transitions in the visible region. In dichloromethane solution they display a one-electron reduction of pap near -0.90V vs SCE and a reversible ruthenium(II)-ruthenium(III) oxidation near 0.70V vs SCE. The [Ru-III(PPh(3))(2)(pap)Cl-2](+) complex cation, generated by coulometric oxidation of [Ru(PPh(3))(2)(pap)Cl-2](+) shows two intense LMCT transitions in the visible region. It oxidizes N,N-dimethylaniline and [Ru-II(bpy)(2)Cl-2] (bpy = 2,2'-bipyridine) to produce N,N,N',N'-tetramethyIbenzidine and [Ru-III(bpy)(2)Cl-2](+) respectively. Reaction of [Ru(PPh(3))(2)(pap)X(2)] with Ag+ in ethanol produces [Ru(PPh(3))(2)(pap)(EtOH)2](2+) which upon further reaction with L (L = pap, bpy, acetylacetonate ion(acac(-)) and oxalate ion (ox(2-))) gives complexes of type [Ru(PPh(3))(2)(pap)(L)](n+) (n = 0, 1, 2). All these diamagnetic complexes show a weak d-d transition and several intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation potential decreases in the order (of L): pap > bpy > acac(-) > ox(2-). Reductions of the coordinated pap and bpy are also observed.