CHEMISTRY OF RUTHENIUM(II) COMPLEXES OF N-SUBSTITUTED 1,2-BENZOQUINONE DIIMINES - SYNTHESIS, STRUCTURE AND REDOX PROPERTIES

A series of ruthenium complexes of N-aryl-1,2-benzoquinone diimine che lates [Ru(acac)(2)L] have been isolated via ruthenium promoted oxidati ve dimerization of arylamines. These compounds were obtained from the reaction of [Ru(acac)(3)] and arylamines. The crystal structure of one representative case has been determined to authenticate the formation of the compound from a heretofore unknown chemical transformation. Th e structural data revealed a planar diimine L, The two C-C (imine) and two conjugate C-C double bonds in the quinonoid ring are localized an d are indicative of the bivalent state of the metal ion. A plausible r eaction pathway is discussed. Extended Huckel calculations on [Ru(acac )(2)L] revealed that the metal-ligand overlap is high. The electronic transitions of the complexes are discussed based on the frontier MO di agram. There are multiple transitions in the range 1100 to 250 nm. The highly intense transition at ca, 520 nm has been assigned to a transi tion involving two heavily mixed metal-ligand orbitals, The diimine co mplexes undergo four successive one electron transfer processes. Two a re metal centered, occurring at positive potentials, and two are ligan d reductions at negative potentials. The E degrees(298) values of all the four redox processes are dependent on the nature of substitution o f the quinone diimine ligand. The structure and physicochemical proper ties of these complexes are compared with those of [Ru(acac)(2)(bqdi)] (bqdi = o-benzoquinone diimine) obtained from the reaction of[Ru(acac )(3)] and o-phenylenediamine.