Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
J Am Chem Soc. 2013 Dec 18;135(50):18876-83. doi: 10.1021/ja408787k. Epub 2013 Dec 9.
Photochemical HX splitting requires the management of two protons and the execution of multielectron photoreactions. Herein, we report a photoinduced two-electron reduction of a polypyridyl Ni(II) chloride complex that provides a route to H2 evolution from HCl. The excited states of Ni complexes are too short to participate directly in HX activation, and hence, the excited state of a photoredox mediator is exploited for the activation of HX at the Ni(II) center. Nanosecond transient absorption (TA) spectroscopy has revealed that the excited state of the polypyridine results in a photoreduced radical that is capable of mediating HX activation by producing a Ni(I) center by halogen-atom abstraction. Disproportionation of the photogenerated Ni(I) intermediate affords Ni(II) and Ni(0) complexes. The Ni(0) center is capable of reacting with HX to produce H2 and the polypyridyl Ni(II) dichloride, closing the photocycle for H2 generation from HCl.
光致化学 HX 分裂需要管理两个质子并执行多电子光反应。在此，我们报告了一种多吡啶镍（II）氯化物配合物的光诱导两电子还原，该反应为从 HCl 中产生 H2 提供了一种途径。镍配合物的激发态太短，无法直接参与 HX 的活化，因此，利用光氧化还原介体的激发态在 Ni(II)中心活化 HX。纳秒瞬态吸收（TA）光谱已表明，多吡啶的激发态导致光还原自由基，该自由基能够通过卤原子的攫取产生 Ni(I)中心来介导 HX 的活化。光生成的 Ni(I)中间体的歧化反应提供 Ni(II)和 Ni(0)配合物。Ni(0)中心能够与 HX 反应生成 H2 和多吡啶镍（II）二氯化物，从而完成从 HCl 中产生 H2 的光循环。
