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• 130247-28-8 (difluoroboryl)diphenylglyoximatocobalt(II) bis(acetonitrile) 

Relevant academic research and scientific papers

Kinetics of electron transfer reactions of H2-evolving cobalt diglyoxime catalysts

Co-diglyoxime complexes catalyze H2 evolution from protic solutions at modest overpotentials. Upon reduction to CoI, a Co III-hydride is formed by reaction with a proton donor. Two pathways for H2 production are analyzed: one is a heterolytic route involving protonation of the hydride to release H2 and generate Co III; the other is a homoytic pathway requiring association of two CoIII-hydrides. Rate constants and reorganization parameters were estimated from analyses of laser flash-quench kinetics experiments (Co III-CoII self-exchange k = 9.5 × 10-8 - 2.6 × 10-5 M-1 s-1; λ = 3.9 (±0.3) eV: CoII-CoI self-exchange k = 1.2 (±0.5) × 105 M-1 s-1; λ = 1.4 (±0.05) eV). Examination of both the barriers and driving forces associated with the two pathways indicates that the homolytic reaction (Co IIIH + CoIIIH → 2 CoII + H2) is favored over the route that goes through a CoIII intermediate (CoIIIH + H+ → CoIII + H2).

Electrocatalytic hydrogen evolution at low overpotentials by cobalt macrocyclic glyoxime and tetraimine complexes

Cobalt complexes supported by diglyoxime ligands of the type Co(dmgBF 2)2(CH3CN)2 and Co(dpgBF 2)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 CH 3CN. 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(dpgBF 2)2(CH3CN)2, [Co(Tim Me)Br2]Br, and [Co(TimMe)(CH 3CN)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(Tim Me)Br2]+, and [Co(TimMe)(CH 3CN)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(dmgBF 2)2(CH3CN)2 determined by electrochemistry. Consistent with this small overpotential, Co(dmgBF 2)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.