Optimized synthesis of a tert-butyl-phenyl-substituted tetrapyridophenazine ligand and its Ru(ii) complexes and determination of dimerization behaviour of the complexes through supramolecular “Fingerhakel”

Abstract

The synthesis of tpphz(tbp)₂ (tpphz(tbp)₂ = 3,16-di(tert-butyl-phenyl)-tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine) has been optimized by using a new synthetic route. The complexes Ru(tbp)₂tpphz, Rutpphz(tbp)₂, Rutpphz(tbp)₂Ru and the reference compound Ru(tbp)₂phen (where Ru = (tbbpy)₂Ru, tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine and (tbp)₂phen = 3,8-bis(4-tert-butyl-phenyl)-1,10-phenanthroline) have been synthesized and characterized. Crystal structures or structural motifs could be obtained for each intermediate and complex and for the first time a tpphz based uncomplexed ligand could be investigated in the solid state. The mononuclear complexes Ru(tbp)₂tpphz and Rutpphz(tbp)₂ form π–π stacked dimers in the solid state. The latter exhibits an interesting aggregation in the solid state with three π-interactions. Concentration dependent aggregation of these isomers in solution is observed with the aid of ¹H-NMR investigations. Out of those dimerization constants (K_D) could be calculated for the complexes Ru(tbp)₂tpphz and Rutpphz(tbp)₂. The values differ significantly. Photophysical and electrochemical properties of the presented complexes were investigated and compared with reference compounds. The tert-butyl-phenyl-substitution induces a stabilization of the ¹MLCT and ³MLCT states localized on the phenanthroline part of the bridging ligand. The ³MLCT localized on the phenazine portion seems to be not or only to a minor extent influenced by these substituents.