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)RuC⋮CR]+ (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), (C6H4C⋮C)nC6H5 [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) Å, respectively. The Ru(III/II) oxidation waves are irreversible for 1−8 (Epa = 0.15−0.26 V vs FeCp2+/0) but reversible for 9 and 10 (E1/2 = 0.99 and 1.00 V, respectively). The absorption bands in the visible region for 1−8 (λmax = 502−526 nm) and 9 and 10 (λmax ca. 410 nm) are assigned as dπ(RuII) → π*(polypyridine) MLCT transitions. Complexes 1−8 weakly emit at λmax = 748−786 nm in CH3CN solution at 298 K (λex = 550 nm). Complexes 9 and 10 are nonemissive in CH2Cl2 solution at 298 K, but in glassy n-butyronitrile at 77 K, excitation at λ = 415 nm produces emission at λmax = 597 and 615 nm, respectively. These emissions are tentatively ascribed as dπ(RuII) → π*(polypyridyl) 3MLCT in nature. The carbene derivatives 9 and 10 undergo photochemical reactions upon irradiation in solution, and [(tpy)(bpy)RuN⋮CCH3]2+ and 4-methoxybenzaldehyde were isolated from the photolysis of 9 in CH3CN.