A Self-Assembled Cofacial Cobalt Porphyrin Prism for Oxygen Reduction Catalysis

J Am Chem Soc. 2017 Feb 1;139(4):1424-1427. doi: 10.1021/jacs.6b12404. Epub 2017 Jan 19.

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 [Ru86-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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Cobalt / chemistry*
  • Coordination Complexes / chemistry*
  • Electrochemical Techniques
  • Electrodes
  • Molecular Structure
  • Oxidation-Reduction
  • Oxygen / chemistry*
  • Porphyrins / chemistry*

Substances

  • Coordination Complexes
  • Porphyrins
  • Cobalt
  • Oxygen