A novel dinuclear ruthenium complex bridged through a substituted phenazine ligand formed by ruthenium-promoted oxidative assembly of 1,3-diaminobenzene.

Abstract

The reaction of [Ru(acac)3] (acac = acetylacetonate) with molten 1,3-diaminobenzene affords the crystalline monometallic compound [Ru(L1)-(acac)21 (1: L1 = N-(3'-aminophenyl)1,2-(3-amino)benzoquinone diimine) along with an unstable dimetallic compound [Ru2(mu-L2)(acac)4] (2: L2=N-4,6-bis(3'-aminophenyl)imino-3,5-diimino-hex-1-ene). Compound 2 transforms to a stable dimetallic compound [Ru2(mu-L3)(acac)4] (3: L3 = 2-amino-6(3'-aminophenyl)imino-9-imino-phenazine) in boiling 2-methoxyethanol. The above compounds are formed by ruthenium-mediated oxidative di- or trimerization of the diamine with the formation of several new C-N bonds. The products have been thoroughly characterized. FAB mass spectra, along with other physicochemical data, were used for their formulations. The compounds 1, 2, and 3 display intense peaks due to their parent molecular ions at m/z 512, 916, and 914, respectively. Final characterization of complex 3 was made by single-crystal X-ray structure determination. The structure of 3 confirmed the formation of three new C-N bonds and the bridging ligand L3 from 1,3-diaminobenzene. The conversion, 2 --> 3 is an oxidative ring-closure reaction, which is associated with dehydrogenation reactions. The monometallic compound 1, showed a reversible metal-based anodic response at 0.35 V. On the other hand, both the compounds 2 and 3 showed a pair of well-resolved metal-based anodic oxidations, for which the separation between the two successive anodic responses were high (>0.4 V). In addition, all of them showed multiple cathodic responses that were in the range -1.0 to -2.0 V.