Ruthenium complexes of quinone related N-aryl-1,2-diimines.: Metal mediated synthesis, X-ray structure and chemical reaction

A family of ruthenium N-aryl-1,2-diiminoarene chelate complexes, [RuCl2(bpy) (diim)], 1 ( bpy = 2,2'-bipyridine, diim = N-aryl-1,2-diiminoarene) were isolated from the reaction of [RuCl3 (bpy)] and a primary aromatic amine (ArNH2) in the presence of aerial oxygen. The diim ligand was formed in situ due to oxidative dimerisation of ArNH2. The metal complex, in this reaction, acts as a mediator. The dichloro complexes were characterized based on their physicochemical data. The X-ray structure of one member of the family was determined and the results used to authenticate the formation of the product from an unusual oxidative fusion of aromatic monoamines. The X-ray structure of 1c (substituent R on the aromatic ring = Cl) revealed a cis geometry with respect to two coordinated chlorides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine oxidation state of the ligand bound to ruthenium in its bivalent oxidation state. These complexes showed multiple transitions in the near-IR and visible regions. The highly intense transition at around 540 nm has been assigned to a transition involving two heavily mixed metal ligand orbitals. The ruthenium( III) / ruthenium( II) couple for the dihalo complexes appeared at a high anodic potential ( range 0.50 to 0.90 V), which for differently substituted compounds depend on the Hammett Sigmasigma(p) parameters of the substitution on the diim ligand. The syntheses and characterization of a few heteroleptic tris-chelates, [Ru(bpy) (diim) L] (ClO4)2.nH(2)O(L = a bidentate N,N-donor), involving the reaction of 1 with two moles of the silver reagent, [AgL2] (ClO4), are reported. The tris-chelates showed intense charge transfer in their electronic spectra and multiple cathodic voltammetric responses, which have been assigned as reductions of coordinated ligands.