Synthesis and characterization of heterooligonuclear ruthenium complexes with tri(phenanthrolino)hexaazatriphenylene ligands

Abstract

A homologous series of homo- and heterooligonuclear ruthenium/palladium complexes of 9,10,19,20,29,30-hexaazahexapyrido[3,2-a:2′,3′-c:3′′,2′′-k:2′′′,3′′′-m:-3′′′′,2′′′′-u:2′′′′′,3′′′′′-w]-trinaphthylene (PHAT) with the formula [{Ru(tbbpy)2} n (μ-phat)]2n+ (n = 1, 2, 3) and [{Ru(tbbpy)2} m (μ-phat){PdCl2}3- m ]2m+ (m = 1, 2) was prepared and characterized, where TBBPY = 4,4′-di-tert-butyl-2,2′-bipyridine. Toward this aim, a new synthetic route was developed for which a microwave-assisted successive complexation reaction of the multitopic ligand was used. In accordance to the only known complex of this kind, [{Ru(phen)2}3(μ-phat)]6+, only the outer 1,10-phenanthroline (PHEN) like coordination spheres of the ligand could be substituted with octahedral ruthenium and square planar palladium fragments. This allows the construction of new supramolecular structures with at least three metal centers that are potentially capable of intramolecular multielectron transfer and photocatalytic redox activity. Electrochemical investigations show that the metal centers in the homonuclear ruthenium complex do not interact and that the ligand-based redox steps are reversible. Preliminary investigations also show that PHAT may be photochemically reduced as seen by UV-Vis spectroscopy; however, no catalytic activity for photochemical hydrogen production could be observed.