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Enhancing the Reactivity of Nickel(II) in Hydrogen Evolution Reactions (HER) by β-Hydrogenation of Porphyrinoid Ligands

Abstract

Fine-tuning of porphyrin β-periphery is important for naturally occurring metal tetrapyrroles to exert diverse biological roles. Here we described that this approach is also applied to design molecular catalysts, as exemplified by Ni(II) porphyrinoids catalyzing hydrogen evolution reaction (HER). We found that β-hydrogenation of porphyrin remarkably enhances electrocatalytic HER reactivity (turnover frequencies of 6287 vs. 265 s-1 for Ni(II) chlorin Ni-2 and porphyrin Ni-1, and of 1737 vs. 342 s-1 for Ni(II) hydroporpholactone Ni-4 and porpholactone Ni-3, respectively) using trifluoroacetic acid (TFA) as the proton source. DFT calculations suggest that, after two-electron reduction, β-hydrogenation renders more electron density located on the Ni center and thus prefers to generate highly reactive nickel hydride intermediate. To demonstrate it, decamethylcobaltocene Co(Cp*)2 was used as a chemical reductant, [Ni-2]2- reacts ca. 30 times faster than [Ni-1]2- with TFA, in line with the electrocatalysis and computational results. Thus, such subtle structural changes inducing the distinctive reactivity of Ni(II) not only tests the fundamental understanding of natural Ni tetrapyrroles also provides a valuable clue to design metal porphyrinoid catalysts.

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Publication details

The article was received on 09 May 2017, accepted on 18 Jun 2017 and first published on 19 Jun 2017


Article type: Edge Article
DOI: 10.1039/C7SC02073B
Citation: Chem. Sci., 2017, Accepted Manuscript
  • Open access: Creative Commons BY-NC license
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    Enhancing the Reactivity of Nickel(II) in Hydrogen Evolution Reactions (HER) by β-Hydrogenation of Porphyrinoid Ligands

    Z. Wu, T. Wang, Y. Meng, Y. Rao, S. Gao, J. Zheng, B. Wang and J. Zhang, Chem. Sci., 2017, Accepted Manuscript , DOI: 10.1039/C7SC02073B

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