Mechanistic Evaluation of a Nickel Proton Reduction Catalyst Using Time-Resolved X-ray Absorption Spectroscopy

• DOI: 10.1021/acs.jpcc.6b06883
• Publication Date: 2016-08-16T02:09:09Z
• Authors: Dooshaye Moonshiram; Alexander Guda; Lars Kohler; Antonio Picon; Sergey Guda; C. Stefan Lehmann; Xiaoyi Zhang; Stephen H. Southw...; Karen L. Mulfort
• Keywords: X-ray absorption spectroscopy

We report the light-induced electronic and geometric changes taking place in "real time" of a multimolecular [Ru(bpy)3]2+/[Ni(PPh2NPh2)2(CH3CN)]2+/ascorbic acid photocatalytic system by time-resolved X-ray absorption spectroscopy (tr-XAS) nano- to microsecond time regime. Using tr-XAS allows us observe diffusion-governed electron transfer between excited photosensitizer nickel(II) proton reduction catalyst on nanosecond scale followed formation transient distorted tetrahedral Ni(I) intermediate. A 50-fold increase decay lifetime species, presence donor, shows that favored catalytic pathway occurs through reductive quenching catalyst. Lack protonation amine groups within our experimental window suggests binding is rate limiting step for H2 photocatalysis this system. This study supported molecular orbital density functional theory (DFT-MO) calculations providing relevant information ongoing synthetic efforts "DuBois-type" nickel complexes as well mechanistic understanding photoevolution processes cycle rational design hydrogen-evolving photocatalysts.