title: Unusually efficient pyridine photodissociation from Ru(II) complexes with sterically bulky bidentate ancillary ligands.
abstract: The introduction of steric bulk to the bidentate ligand in [Ru(tpy)(bpy)(py)](2+) (1; tpy = 2,2':2',6″-terpyridine; bpy = 2,2'-bipyridine; py = pyridine) to provide [Ru(tpy)(Me2bpy)(py)](2+) (2; Me2bpy = 6,6'-dimethyl-2,2'-bipyridine) and [Ru(tpy)(biq)(py)](2+) (3; biq = 2,2'-biquinoline) facilitates photoinduced dissociation of pyridine with visible light. Upon irradiation of 2 and 3 in CH3CN (λirr = 500 nm), ligand exchange occurs to produce the corresponding [Ru(tpy)(NN)(NCCH3)](2+) (NN = Me2bpy, biq) complex with quantum yields, Φ500, of 0.16(1) and 0.033(1) for 2 and 3, respectively. These values represent an increase in efficiency of the reaction by 2-3 orders of magnitude as compared to that of 1, Φ500 < 0.0001, under similar experimental conditions. The photolysis of 2 and 3 in H2O with low energy light to produce [Ru(tpy)(NN)(OH2)](2+) (NN = Me2bpy, biq) also proceeds rapidly (λirr > 590 nm). Complexes 1-3 are stable in the dark in both CH3CN and H2O under similar experimental conditions. X-ray crystal structures and theoretical calculations highlight significant distortion of the planes of the bidentate ligands in 2 and 3 relative to that of 1. The crystallographic dihedral angles defined by the bidentate ligand, Me2bpy in 2 and biq in 3, and the tpy ligand were determined to be 67.87° and 61.89°, respectively, whereas only a small distortion from the octahedral geometry is observed between bpy and tpy in 1, 83.34°. The steric bulk afforded by Me2bpy and biq also result in major distortions of the pyridine ligand in 2 and 3, respectively, relative to 1, which are believed to weaken its σ-bonding and π-back-bonding to the metal and play a crucial role in the efficiency of the photoinduced ligand exchange. The ability of 2 and 3 to undergo ligand exchange with λirr > 590 nm makes them potential candidates to build photochemotherapeutic agents for the delivery of drugs with pyridine binding groups.
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Knoll
authors.forename: Bryan A
authors.initials: BA
authors.lastname: Albani
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Durr
authors.forename: Claudia
authors.initials: C
authors.lastname: Turro
mesh_terms: D018360:Crystallography, X-Ray; D008027:Light; D008956:Models, Chemical; D010782:Photolysis; D066244:Proton Magnetic Resonance Spectroscopy; D011725:Pyridines / Q000737:chemistry*; D017975:Ruthenium Compounds / Q000737:chemistry*; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry
chemical_list: D011725:Pyridines; D017975:Ruthenium Compounds; D014867:Water