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

Despite the high it-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 pi-pi 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-o'(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-o'(Ru3+/2+) also is quantitatively described using a summative Hammett parameter (sigma(T)), as well as using Lever's electrochemical parameters (E-L). Recommended parametrizations for substituted 2,2'-bipyridyl and 1,10-phenanthrolinyl ligands were derived from analysis of correlations of E-o'(Ru3+/2+) for 99 homo- and heteroleptic ruthenium(II) tris-diimine complexes. This analysis reveals that variations in E-o'(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 sigma(+)(p) than either sigma(m) or sigma(p). Substituents at the 5- and 6-positions of phenanthrolinyl ligands are best described by sigma(m) and have effects comparable to those of substituents at the 3- and 8-positions. Correlations of E-L with sigma(T) for 1,10-phenanthrolinyl and 2,2'-bipyridyl ligands show similar results, except that sigma(p) and sigma(+)(p) are almost equally effective in describing the influence of substituents at the 4- and 4'-positions of bipyridyl ligands. MLCT energies and d(5)/d(6)-electron redox couples of the complexes with 5-substituted 1,10-phenanthroline exhibit correlations with values for other d(6)-electron metal complexes that can be rationalized in terms of the relative number of diimine ligands and substituents.