Electrocatalytic Hydrogen Evolution at Low Overpotentials by Cobalt Macrocyclic Glyoxime and Tetraimine Complexes
Top Cited Papers
- 28 June 2007
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 129 (29), 8988-8998
- https://doi.org/10.1021/ja067876b
Abstract
Cobalt complexes supported by diglyoxime ligands of the type Co(dmgBF2)2(CH3CN)2 and Co(dpgBF2)2(CH3CN)2 (where dmgBF2 is difluoroboryl-dimethylglyoxime and dpgBF2 is difluoroboryl-diphenylglyoxime), as well as cobalt complexes with [14]-tetraene-N4 (Tim) ligands of the type [Co(TimR)X2]n+ (R = methyl or phenyl, X = Br or CH3CN; n = 1 with X = Br and n = 3 with X = CH3CN), have been observed to evolve H2 electrocatalytically at potentials between −0.55 V and −0.20 V vs SCE in CH3CN. The complexes with more positive Co(II/I) redox potentials exhibited lower activity for H2 production. For the complexes Co(dmgBF2)2(CH3CN)2, Co(dpgBF2)2(CH3CN)2, [Co(TimMe)Br2]Br, and [Co(TimMe)(CH3CN)2](BPh4)3, bulk electrolysis confirmed the catalytic nature of the process, with turnover numbers in excess of 5 and essentially quantitative faradaic yields for H2 production. In contrast, the complexes [Co(TimPh/Me)Br2]Br and [Co(TimPh/Me)(CH3CN)2](BPh4)3 were less stable, and bulk electrolysis only produced faradaic yields for H2 production of 20−25%. Cyclic voltammetry of Co(dmgBF2)2(CH3CN)2, [Co(TimMe)Br2]+, and [Co(TimMe)(CH3CN)2]3+ in the presence of acid revealed redox waves consistent with the Co(III)−H/Co(II)−H couple, suggesting the presence of Co(III) hydride intermediates in the catalytic system. The potentials at which these Co complexes catalyzed H2 evolution were close to the reported thermodynamic potentials for the production of H2 from protons in CH3CN, with the smallest overpotential being 40 mV for Co(dmgBF2)2(CH3CN)2 determined by electrochemistry. Consistent with this small overpotential, Co(dmgBF2)2(CH3CN)2 was also able to oxidize H2 in the presence of a suitable conjugate base. Digital simulations of the electrochemical data were used to study the mechanism of H2 evolution catalysis, and these studies are discussed.Keywords
This publication has 17 references indexed in Scilit:
- Cobaloximes as Functional Models for Hydrogenases. 2. Proton Electroreduction Catalyzed by Difluoroborylbis(dimethylglyoximato)cobalt(II) Complexes in Organic MediaInorganic Chemistry, 2007
- Chemical Redox Agents for Organometallic ChemistryChemical Reviews, 1996
- Hydrogen bonding between guanosine 5'-monophosphate and coordinatively saturated cobalt(III) and platinum(II) ammine and ethylenediamine complex cationsInorganic Chemistry, 1991
- Reduction-induced cleavage of the cobalt-carbon bond in macrocyclic organocobalt complexesInorganic Chemistry, 1991
- AXIAL LABILIZATION BY MACROCYCLIC LIGANDS. 5. AXIAL SUBSTITUTION IN Co(III) COMPLEXES OF A SERIES OF 14-MEMBERED TETRAAZA MACROCYCLIC LIGANDSJournal of Coordination Chemistry, 1986
- Acid-base equilibria in organic solvents : Part 1. Evaluation of solvent basicity by cyclic voltammetryAnalytica Chimica Acta, 1985
- Unimolecular and bimolecular homolytic reactions of organochromium and organocobalt complexes. Kinetics and equilibriaJournal of the American Chemical Society, 1984
- Electrocatalytic reduction of carbon dioxide by using macrocycles of nickel and cobaltJournal of the American Chemical Society, 1980
- Tetrasubstituted [14]-1,3,8,10-tetraeneN4 macrocyclic complexes: synthesis, organic precursor, and template reaction mechanismInorganic Chemistry, 1980
- Synthesis of hydroxy-substituted macrocyclic ligand complexes of cobalt and isolation of a macrocycle precursorInorganic Chemistry, 1977