Synthesis and characterization of 4’-substituted-2,2’:6’,2”-terpyridine ruthenium (ll) complexes

Abstract

Derivate terpyridine ligands have been synthesized, following the combination of two reactions: the Michael addition and the Kröhnke condensation, giving rise to 4’-(4-bromophenyl)-2,2’:6’,2”-terpyridine (3a) and 4’-(4-aniline)-2,2’:6’,2”-terpyridine (3b). The reaction of 4'-chloro-2,2':6',2''-terpyridine or 3a with naphthalen-2-ylmethanol produces 4’-(naphthalen-2-ylmethoxy)-2,2’:6’,2”-terpyridine (3c) or 4’-(4-(naphthalen-2-ylmethoxy)phenyl)-2,2’:6’,2”-terpyridine (3d), respectively. These ligands react with RuCl3·3H2O to give ruthenium (III) complexes: [Ru(Brtrp)Cl3] (4a), [Ru(Anitrp)Cl3] (4b), [Ru(Ntrp)Cl3] (4c) and [Ru(BrNtrp)Cl3](4d). Their reduction and the substitution of the two chloride for bidentate N,N ligands, such as 2,2'-bipyridine, 1,10-phenanthroline or 2,2’-dipyridylamine allows to obtain [Ru(Brtrp)(bipy)Cl]Cl (5a), [Ru(Brtrp)(phen)Cl]Cl (5a’), [Ru(Brtrp)(dpa)Cl]Cl (5a”), and [Ru(Ntrp)(bipy)Cl]Cl (5c). In order to try to modify their photochemical properties, the complexes [Ru(Brtrp)(N,N)(py)](PF6)2, where N, N = bipy (6a), phen (6a’), dpa (6a”) have been obtained from (5a-a”) by substitution of the chlorine atom coordinated to the ruthenium for a pyridine group. Also the complexes with two terpyridine ligands [Ru(Brtrp)2](PF6)2 (7a) and [Ru(Brtrp)(Ntrp)](PF6)2 (7b) were synthesized. The ligands and the ruthenium (II) complexes have been characterized by infrared spectroscopy (IR), mass spectrometry, and when it has been possible, by mono- and bidimensional NMR spectroscopies. Furthermore, the determination of the absorbance of the synthesized compounds by UV-vis and their fluorescence by emission and excitation spectra were carried out. Finally, the interaction of some of the complexes with DNA has been studied by UV-Vis and electrophoresis. The results obtained from these techniques indicate that the synthesized complexes have a covalent and/or intercalation interaction with DNA and for complexes 5a and 7a a moderately strong intrinsic binding constant.