title: A Ru(II) bis-terpyridine-like complex that catalyzes water oxidation: the influence of steric strain.
abstract: The complexation of 2,9-dicarboxy-1,10-phenanthroline (DPA) with [Ru(tpy)Cl3] (tpy = 2,2';6,2″-terpyridine) provides a six-coordinate species in which one carboxyl group of DPA is not bound to the Ru(II) center. A more soluble tri-t-butyl tpy analogue is also prepared. Upon oxidation, neither species shows evidence for intramolecular trapping of a seven-coordinate intermediate. The role of the tpy ligand is revealed by the preparation of [Ru(tpy)(phenq)](2+) (phenq = 2-(quinol-8'-yl)-1,10-phenanthroline) that behaves as an active water oxidation catalyst (TON = 334). This activity is explained by the expanded coordination geometry of the phenq ligand that can form a six-membered chelate ring that better accommodates the linear arrangement of axial ligands required for optimal pentagonal bipyramid geometry. When a 1,8-naphthyidine ring is substituted for each of the two peripheral pyridine rings on tpy, increased crowding in the vicinity of the metal center impedes acquisition of the prerequisite reaction geometry.
authors.affiliation: Department of Chemistry, 110 Fleming Building, University of Houston , Houston, Texas 77204-5003, United States.
authors.forename: Nattawut
authors.initials: N
authors.lastname: Kaveevivitchai
authors.forename: Lars
authors.initials: L
authors.lastname: Kohler
authors.forename: Ruifa
authors.initials: R
authors.lastname: Zong
authors.forename: Maya
authors.initials: M
authors.lastname: El Ojaimi
authors.forename: Nirja
authors.initials: N
authors.lastname: Mehta
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D011725:Pyridines; D014867:Water; D012428:Ruthenium; C023666:pyridine