Beckman Institute, California Institute of Technology, Pasadena, California 91125, USA.
J Am Chem Soc. 2010 Jan 27;132(3):1060-5. doi: 10.1021/ja9080259.
Co-diglyoxime complexes catalyze H(2) evolution from protic solutions at modest overpotentials. Upon reduction to Co(I), a Co(III)-hydride is formed by reaction with a proton donor. Two pathways for H(2) production are analyzed: one is a heterolytic route involving protonation of the hydride to release H(2) and generate Co(III); the other is a homoytic pathway requiring association of two Co(III)-hydrides. Rate constants and reorganization parameters were estimated from analyses of laser flash-quench kinetics experiments (Co(III)-Co(II) self-exchange k = 9.5 x 10(-8) - 2.6 x 10(-5) M(-1) s(-1); lambda = 3.9 (+/-0.3) eV: Co(II)-Co(I) self-exchange k = 1.2 (+/-0.5) x 10(5) M(-1) s(-1); lambda = 1.4 (+/-0.05) eV). Examination of both the barriers and driving forces associated with the two pathways indicates that the homolytic reaction (Co(III)H + Co(III)H --> 2 Co(II) + H(2)) is favored over the route that goes through a Co(III) intermediate (Co(III)H + H(+) --> Co(III) + H(2)).
共二肟配合物在适度过电势下催化质子溶液中的氢气释放。还原为 Co(I) 后，与质子供体反应形成 Co(III)-氢化物。分析了两种产氢途径：一种是异裂途径，涉及氢化物质子化以释放 H(2)并生成 Co(III)；另一种是均裂途径，需要两个 Co(III)-氢化物的缔合。通过激光闪光猝灭动力学实验的分析来估计速率常数和重组参数（Co(III)-Co(II) 自交换 k = 9.5 x 10(-8) - 2.6 x 10(-5) M(-1) s(-1)；lambda = 3.9 (+/-0.3) eV：Co(II)-Co(I) 自交换 k = 1.2 (+/-0.5) x 10(5) M(-1) s(-1)；lambda = 1.4 (+/-0.05) eV）。对两种途径相关的势垒和驱动力的考察表明，均裂反应（Co(III)H + Co(III)H --> 2 Co(II) + H(2)）比经过 Co(III)中间体的途径（Co(III)H + H(+) --> Co(III) + H(2)）更有利。
