Ruthenium(II) σ-acetylide and carbene complexes supported by the terpyridine-bipyridine ligand set:: Structural, spectroscopic, and photochemical studies

A series of acetylide- and carbene-ruthenium complexes containing polypyridine ligands, [(tpy)(bpy)RuCdropCR](+) (tpy = 2,2':6',2"-terpyridine, bpy = 2,2'-bipyridine; R = C6H4F-4 (1), C6H4Cl-4 (2), C6H5 (3), C6H4Me-4 (4), C6H4OMe-4 (5), t-Bu (6), (C(6)H(4)CdropC)(n)C6H5 [n = 1 (7) and 2 (8)]) and [(tpy)(bpy)Ru=C(OMe)(CH2R)](2+) (R = C6H4OMe-4 (9), t-Bu (10)) have been prepared. The molecular structures of 4(PF6), 5(PF6), and 9(ClO4)(2) reveal Ru-C distances of 2.025(9), 2.025(7), and 1.933(6) Angstrom, respectively. The Ru(III/II) oxidation waves are irreversible for 1-8 (E-pa = 0.15-0.26 V vs FeCp2+/0) but reversible for 9 and 10 (E-1/2 = 0.99 and 1.00 V, respectively). The absorption bands in the visible region for 1-8 (lambda(max) = 502-526 nm) and 9 and 10 (lambda(max) ca. 410 nm) are assigned as d(pi)(Ru-II) --> pi*(polypyridine) MLCT transitions. Complexes 1-8 weakly emit at lambda(max) = 748-786 nm in CH3CN solution at 298 K (lambda(ex) = 550 nm). Complexes 9 and 10 are nonemissive in CH2Cl2 solution at 298 K, but in glassy n-butyronitrile at 77 K, excitation at lambda = 415 nm produces emission at lambda(max) = 597 and 615 nm, respectively. These emissions are tentatively ascribed as d(pi)(Ru-II) --> pi*(polypyridyl) 3 MLCT in nature. The carbene derivatives 9 and 10 undergo photochemical reactions upon irradiation in solution, and [(tpy)(bpy)RuNdropCCH(3)](2+) and 4-methoxybenzaldehyde were isolated from the photolysis of 9 in CH3CN.