title: A Self-Assembled Cofacial Cobalt Porphyrin Prism for Oxygen Reduction Catalysis.
abstract: Herein we report the first study of the oxygen reduction reaction (ORR) catalyzed by a cofacial porphyrin scaffold accessed in high yield (overall 53%) using coordination-driven self-assembly with no chromatographic purification steps. The ORR activity was investigated using chemical and electrochemical techniques on monomeric cobalt(II) tetra(meso-4-pyridyl)porphyrinate (CoTPyP) and its cofacial analogue [Ru8(η6-iPrC6H4Me)8(dhbq)4(CoTPyP)2][OTf]8(Co Prism) (dhbq = 2,5-dihydroxy-1,4-benzoquinato, OTf = triflate) as homogeneous oxygen reduction catalysts. Co Prism is obtained in one self-assembly step that organizes six total building blocks, two CoTPyP units and four arene-Ru clips, into a cofacial motif previously demonstrated with free-base, Zn(II), and Ni(II) porphyrins. Turnover frequencies (TOFs) from chemical reduction (66 vs 6 h-1) and rate constants of overall homogeneous catalysis (kobs) determined from rotating ring-disk experiments (1.1 vs 0.05 h-1) establish a cofacial enhancement upon comparison of the activities of Co Prism and CoTPyP, respectively. Cyclic voltammetry was used to initially probe the electrochemical catalytic behavior. Rotating ring-disk electrode studies were completed to probe the Faradaic efficiency and obtain an estimate of the rate constant associated with the ORR.
authors.affiliation: Department of Chemistry, University at Buffalo, The State University of New York , Buffalo, New York 14260, United States.
authors.forename: Amanda N
authors.initials: AN
authors.lastname: Oldacre
authors.affiliation: Department of Chemistry, University at Buffalo, The State University of New York , Buffalo, New York 14260, United States.
authors.forename: Alan E
authors.initials: AE
authors.lastname: Friedman
authors.affiliation: Department of Chemistry, University at Buffalo, The State University of New York , Buffalo, New York 14260, United States.
authors.forename: Timothy R
authors.identifier: 0000-0002-7668-8089
authors.initials: TR
authors.lastname: Cook
mesh_terms: D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D055664:Electrochemical Techniques; D004566:Electrodes; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D011166:Porphyrins; D003035:Cobalt; D010100:Oxygen