Chemistry of ruthenium in N_2P_2X_2 (X = Cl, Br) coordination sphere: Synthesis, characterization and reactivities

摘要

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh_3)_3X_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. Indichloromethane 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)_2Ci_2] (bpy = 2,2'-bipyridine) to produce N,N,N',N'-tetramethylbenzidine and [Ru~(III)(bpy)_2Cl_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 thecoordinated pap and bpy are also observed.