Catalytic hydrogen evolution from a covalently linked dicobaloxime

• Published in: Proceedings of the National Academy of Sciences - PNAS 2012-09, Vol.109 (39), p.15589-15593
• Main Authors: Valdez, Carolyn N, Dempsey, Jillian L, Brunschwig, Bruce S, Winkler, Jay R, Gray, Harry B
• Format: Article
• Language: English
• Subjects: acetonitrile; Acetonitriles - chemistry; Catalysis; Catalysts; CHEMICAL APPROACHES TO ARTIFICIAL PHOTOSYNTHESIS: SOLAR FUELS SPECIAL FEATURE; cobalt; electrochemistry; Electrodes; Ethers; Evolution; Hydrogen; Hydrogen - chemistry; hydrogen production; Ligands; Models, Chemical; Molecular evolution; Organometallic Compounds - chemistry; Physical Sciences; Protons; Pyridines; Solvents; Tosyl Compounds - chemistry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1118329109

A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p -toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (k ₐₚₚ = 1100 ± 70 M ⁻¹ s ⁻¹). Electrochemical experiments reveal no significant enhancement in the rate of H ₂ evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H ₂ evolution likely occurs by protonation of reductively generated Co ᴵᴵH rather than homolysis of two Co ᴵᴵᴵH units.