화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.135, No.50, 18876-18883, 2013
Two-Electron HCl to H-2 Photocycle Promoted by Ni(II) Polypyridyl Halide Complexes
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 H-2 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 H-2 and the polypyridyl Ni(II) dichloride, closing the photocycle for H-2 generation from HCl.