Reactivity of the transition metal complexes containing azo, triazine, and hydrazone ligands

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This work initially arose from our research interest in the preparation of photo-and thermal-responsive metal complexes. Azoaromatic compounds are highly colored and have long been used as dyes and pigments. It is well known that the azo group is photoreactive and isomerizes between trans and cis conformers by irradiation of the π-π^* bands.We prepared new triazine ligands derived from 1-phenylazo-2-naphtylamine and pyridine-2-aldehyde or quinoline-2-aldehyde, and their palladium(II) complexes. The reversible ring opening and closure reactions of the coordinating dihydrotriazine ligand were observed by the addition of MeOH and (^nBu)_4NCl. The reaction can be understood in terms of competition between MeO^-and Cl^-ions.We, then, prepared hydrazone ligands derived from 2-hydrazinopyridine and 2-(alkylthio)benzaldehyde (R=Me,^tBu,4-chlorophenyl) or 2-(diphenylphosphino)beozaldehyde, and their metal complexes (M=Pd(II) and Pt(II). The NH hydrogen atoms of the coordinated hydrazone ligands were easily deprotonated, and protonated by the action of an acid. The reaction was followed spectrophotometrically, and the isosbestic points were observed. The uncoordinated hydrazone ligands and their palladium(II) complexes was not emissive, however, the platinum(II) complexes showed strong emission peaks in the visible region. Reversible large sifts of the emission peaks were observed by the action of acids and bases.