Electrocatalytic hydrogen evolution at low overpotentials by cobalt macrocyclic glyoxime and tetraimine complexes
Electrocatalytic hydrogen evolution at low overpotentials by cobalt macrocyclic glyoxime and tetraimine complexes
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DOI：
10.1021/ja067876b
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发表时间：
2007-07-25
影响因子：
15
通讯作者：
Peters, Jonas C.
中科院分区：
文献类型：
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作者：
Hu, Xile;Brunschwig, Bruce S.;Peters, Jonas C.
钴配合物由Co(dmgBF(2))(2)(CH(3)CN)(2)和Co(dpgBF(2))(2)(CH(3)CN)(2) (dmgBF(2))(2)(CH(3)CN)（其中dmgBF（2)是二氟硼基二甲基乙氧基二甲基乙氧基二甲基乙氧基二苯乙氧基二苯乙氧基二苯乙氧基），dpgBF(2)是二氟硼基二苯乙氧基二苯乙氧基）配体支持，以及钴配合物与[14]-四烯- n (4) (Tim) [Co(Tim(R))X(2)](n+) (R =甲基或苯基，X = Br或CH(3)CN)；n = 1 （X = Br）和n = 3 （X = CH(3)CN）在-0.55 V和-0.20 V与SCE在CH(3)CN中的电催化作用下发生H(2)的演化。Co（II/I）氧化还原电位较高的配合物产生H(2)的活性较低。对于配合物Co(dmgBF(2))(2)(CH(3)CN)(2), Co(dpgBF(2))(2)(CH(3)CN)(2), [Co(Tim(Me))Br(2)]Br和[Co(Tim(Me))(CH(3)CN)(2)](BPh(4))(3))，本体电解证实了该过程的催化性质，周转量超过5，基本上是H(2)生产的定量法拉第产率。相比之下，配合物[Co(Tim(Ph/Me))Br(2)]Br和[Co(Tim(Ph/Me))(CH(3)CN)(2)](BPh（4))(3)）的稳定性较差，体电解产生H(2)的法拉第产率仅为20-25%。在酸的存在下，用循环伏安法对Co(dmgBF(2))(2)(CH(3)CN)(2)、[Co(Tim(Me))Br(2)]（+）和[Co(Tim(Me))(CH(3)CN)(2)]（3+）进行了氧化还原，结果表明催化体系中存在Co(III)-H/Co(II)-H对，表明催化体系中存在Co（III）氢化物中间体。这些Co配合物催化H(2)演化的电位与报道的CH(3)CN中质子生成H(2)的热力学电位接近，Co(dmgBF(2))(2)(CH(3)CN)(2)的最小过电位为40 mV。与这个小过电位一致，Co(dmgBF(2))(2)(CH(3)CN)(2)在合适的共轭碱存在下也能氧化H(2)。利用电化学数据的数字模拟研究了氢(2)的演化催化机理，并对这些研究进行了讨论。
Cobalt complexes supported by diglyoxime ligands of the type Co(dmgBF(2))(2)(CH(3)CN)(2) and Co(dpgBF(2))(2)(CH(3)CN)(2) (where dmgBF(2) is difluoroboryl-dimethylglyoxime and dpgBF(2) is difluoroboryl-diphenylglyoxime), as well as cobalt complexes with [14]-tetraene-N(4) (Tim) ligands of the type [Co(Tim(R))X(2)](n+) (R = methyl or phenyl, X = Br or CH(3)CN; n = 1 with X = Br and n = 3 with X = CH(3)CN), have been observed to evolve H(2) electrocatalytically at potentials between -0.55 V and -0.20 V vs SCE in CH(3)CN. The complexes with more positive Co(II/I) redox potentials exhibited lower activity for H(2) production. For the complexes Co(dmgBF(2))(2)(CH(3)CN)(2), Co(dpgBF(2))(2)(CH(3)CN)(2), [Co(Tim(Me))Br(2)]Br, and [Co(Tim(Me))(CH(3)CN)(2)](BPh(4))(3), bulk electrolysis confirmed the catalytic nature of the process, with turnover numbers in excess of 5 and essentially quantitative faradaic yields for H(2) production. In contrast, the complexes [Co(Tim(Ph/Me))Br(2)]Br and [Co(Tim(Ph/Me))(CH(3)CN)(2)](BPh(4))(3) were less stable, and bulk electrolysis only produced faradaic yields for H(2) production of 20-25%. Cyclic voltammetry of Co(dmgBF(2))(2)(CH(3)CN)(2), [Co(Tim(Me))Br(2)](+), and [Co(Tim(Me))(CH(3)CN)(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 H(2) evolution were close to the reported thermodynamic potentials for the production of H(2) from protons in CH(3)CN, with the smallest overpotential being 40 mV for Co(dmgBF(2))(2)(CH(3)CN)(2) determined by electrochemistry. Consistent with this small overpotential, Co(dmgBF(2))(2)(CH(3)CN)(2) was also able to oxidize H(2) in the presence of a suitable conjugate base. Digital simulations of the electrochemical data were used to study the mechanism of H(2) evolution catalysis, and these studies are discussed.