Ruthenium Bis-diimine Complexes with a Chelating Thioether Ligand: Delineating 1,10-Phenanthrolinyl and 2,2′-Bipyridyl Ligand Substituent Effects

Despite the high π-acidity of thioether donors, ruthenium­(II) complexes with a bidentate 1,2-bis­(phenyl­thio)­ethane (dpte) ligand and two chelating diimine ligands (i.e., Ru­(diimine)2­(dpte)2+) exhibit room-temperature fluid solution emission originating from a lowest MLCT excited state (diimine = 2,2′-bipyridine, 5,5′-dimethyl-2,2′-bipyridine 4,4′-di-tert-butyl-2,2′-bipyridine, 1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-bromo-1,10-phenanthroline, 5-nitro-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, and 3,4,7,8-tetramethyl-1,10-phenanthroline). Crystal structures show that the complexes form 2 of the 12 possible conformational/configurational isomers, as well as nonstatistical distributions of geometric isomers; there also are short intramolecular π–π interactions between the diimine ligands and dpte phenyl groups. The photoinduced solvolysis product, [Ru­(diimine)2­(CH3CN)2]­(PF6)2, for one complex in acetonitrile also was characterized by single-crystal X-ray diffraction. Variations in the MLCT energies and Ru­(III/II) redox couple, E°′(Ru3+/2+), can be understood in terms of the influence of the donor properties of the ligands on the mainly metal-based HOMO and mainly diimine ligand-based LUMO. E°′(Ru3+/2+) also is quantitatively described using a summative Hammett parameter (σT), as well as using Lever’s electrochemical parameters (EL). Recommended parametrizations for substituted 2,2′-bipyridyl and 1,10-phenanthrolinyl ligands were derived from analysis of correlations of E°′(Ru3+/2+) for 99 homo- and heteroleptic ruthenium­(II) tris-diimine complexes. This analysis reveals that variations in E°′(Ru3+/2+) due to substituents at the 4- and 4′-positions of bipyridyl ligands and 4- and 7-positions of phenanthrolinyl ligands are significantly more strongly correlated with σp+ than either σm or σp. Substituents at the 5- and 6-positions of phenanthrolinyl ligands are best described by σm and have effects comparable to those of substituents at the 3- and 8-positions. Correlations of EL with σT for 1,10-phenanthrolinyl and 2,2′-bipyridyl ligands show similar results, except that σp and σp+ are almost equally effective in describing the influence of substituents at the 4- and 4′-positions of bipyridyl ligands. MLCT energies and d5/d6-electron redox couples of the complexes with 5-substituted 1,10-phenanthroline exhibit correlations with values for other d6-electron metal complexes that can be rationalized in terms of the relative number of diimine ligands and substituents.