1-(2'-Pyridylazo)-2-naphtholate complexes of ruthenium: synthesis, characterization, and DNA binding properties

Reaction of 1-(2'-pyridylazo)-2-naphthol (Hpan) with [Ru(dmso)<SUB>4</SUB>Cl<SUB>2</SUB>] (dmso = dimethylsulfoxide), [Ru(trpy)Cl<SUB>3</SUB>] (trpy = 2,2',2"-terpyridine), [Ru(bpy)Cl<SUB>3</SUB>] (bpy = 2,2'-bipyridine) and [Ru(PPh<SUB>3</SUB>)<SUB>3</SUB>Cl<SUB>2</SUB>] in refluxing ethanol in the presence of a base (NEt<SUB>3</SUB>) affords, respectively, the [Ru(pan)<SUB>2</SUB>], [Ru(trpy)(pan)]<SUP>+</SUP> (isolated as perchlorate salt), [Ru(bpy)(pan)Cl] and [Ru(PPh<SUB>3</SUB>)<SUB>2</SUB>(pan)Cl] complexes. Structures of these four complexes have been determined by X-ray crystallography. In each of these complexes, the pan ligand is coordinated to the metal center as a monoanionic tridentate N,N,O-donor. Reaction of the [Ru(bpy)(pan)Cl] complex with pyridine (py) and 4-picoline (pic) in the presence of silver ion has yielded the [Ru(bpy)(pan)(py)]<SUP>+</SUP> and [Ru(bpy)(pan)(pic)]<SUP>+</SUP> complexes (isolated as perchlorate salts), respectively. All the complexes are diamagnetic (low-spin d<SUP>6</SUP>, S = 0) and show characteristic <SUP>1</SUP>H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a Ru(II)-Ru(III) oxidation on the positive side of SCE. Except in the [Ru(pan)<SUB>2</SUB>] complex, a second oxidative response has been observed in the other five complexes. Reductions of the coordinated ligands have also been observed on the negative side of SCE. The [Ru(trpy)(pan)]ClO<SUB>4</SUB>, [Ru(bpy)(pan)(py)]ClO<SUB>4</SUB>, and [Ru(bpy)(pan)(pic)]ClO<SUB>4</SUB> complexes have been observed to bind to DNA, but they have not been able to cleave super-coiled DNA on UV irradiation