Ferric-Chloride-Promoted Oxidation ofp-Anisidine to anN-Substituted Phenazine Derivative − Structural Elucidation, Protic Equilibria and Coordination Chemistry of the Phenazine

Abstract

The reaction of hydrated ferric chloride and p-anisidine affords brown 6-p-anisyl-2-(p-anisylamino)-9-methoxy phenazine-3(4H)-p-anisylimine (LH) in moderate yield (35%). Plausible steps involved in this unusual fusion process are proposed. This phenazine spontaneously binds with H+ to give a violet solution, pK for the reaction LH + H+ LH2+ is 6.61 at 300 K. The protonated phenazine has been isolated as its chloride salt, [LH2Cl], the structure of which is described in authenticating the formation of LH directly from p-anisidine. The structural data reveal a planar dibenzo pyrazine moiety with an extensive delocalisation along the phenazine backbone. The protonation of LH occurs at the imine nitrogen. The spectral properties of both LH and [LH2]Cl are described. Both show well-resolved 1H NMR spectra with four methyl resonances occurring in the range δ = 3.70 to 3.93. While [LH2]Cl shows two NH resonances at δ = 11.95 and 10.18, neutral LH displays only one such resonance at δ = 8.49. Aromatic proton resonances for these compounds appeared in the range δ = 5.79 to 8.04. The coordination abilities of the above phenazine were explored. It reacts spontaneously with [M(aap)2X2]n+ (M = RuII, OsII; aap = 2-(arylazo)pyridine; X = solvent, n = 2; X = Br−, n = 0) to give cationic complexes of the general formula, [M(aap)2L]+ which were isolated as their perchlorate and bromide salts. These metal complexes were fully characterized. Their spectral properties indicate a bidentate anionic chelation of L−, with deprotonation of the amine nitrogen. The complexes show multiple redox responses. The oxidised complexes are unstable and undergo chemical transformations. The reduction processes, on the other hand, are electrochemically reversible and presumably occur at the coordinated aap ligands.