Two novel reactions of a ruthenium-coordinated phenazine -: Oxidative aromatic ring hydroxylation and dimerization via a new C-N bond formation

The reaction of [Ru(CH3OH)(2)(N boolean AND N)(2)](2+) [N boolean AND N = 2,2'-bipyridine (bpy) and 1,10-ortho-phenanthroline(phen)] with the phenazine ligand, [HL1 = 6-p-anisyl-2-(p-anisylamino)-3(4H)-p-anisylimine-9-methoxyphenazine] in the presence of a base (NEt3) afforded two mononuclear ruthenium complexes, [Ru(L-1)(N boolean AND N)(2)]X (2), and [Ru(LO)(N boolean AND N)(2)]X-2 (3), [LO = 7-methoxy-5-(4-methoxyphenyl)-2,3-bis(4-methoxyphenylimino)-3,5-dihydro-2H-phenazin-1-one] together with a diruthenium complex [(N boolean AND N)(2)(RuLRu)-Ru-2(N boolean AND N)(2)]X-3 (4), [L-2 = 7,8'-dimethoxy-5,10'-bis(4-methoxyphenyl)-2,3'-bis(4-methoxy-phenylamino)-3,2'-bis(4'-methoxyphenylimino)-3,5,2',10'- tetrahydro-[1,5']biphenazinyl-5'-ylium], (X = ClO4- or CF3SO3-). The complexes 3 and 4 were also obtained from the pure complex 2 under two different experimental conditions. Oxidative aromatic ring hydroxylation of the complex 2 produced 3 while the diruthenium complex, 4, was formed by dimerization of 2 via a new C-N bond formation. The products were thoroughly characterized with the help of H-1 NMR and ESI-MS spectral measurements. Final authentication of the two complexes of the transformed phenazine ligands viz. 3 and 4 were made by single-crystal X-ray structure determination of the two representative complexes. These compounds are intensely colored and show transitions in the visible region, which are ascribed as metal-to-ligand charge transfer (MLCT). Notably, intensities of the two MLCT of the compound 4 are significantly higher than those of 2 and 3. Redox properties of the complexes are reported. Electrochemical oxidation of compound 2, even in the presence of trace moisture, produced compound 3. Cyclic voltammetry of compound 3 shows a reductive response near -0.35 V. Its one-electron reduced product is blue and shows an intense EPR signal at g = 2.001. The voltammogram of the diruthenium complex 4 consists of two responses near 0.70 and 0.85 V. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)