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

Abstract

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 ∑σ_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·nH₂O (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.