NDLI: Water-assisted proton delivery and removal in bio-inspired hydrogen production catalysts

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Dupuis, Michel Dubois, Daniel L. O'hagan, Molly Bullock, R. Morris Shaw, Wendy J. Ho, Ming-hsun Raugei, Simone
Description	Author Affiliation: Ho MH ( Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA 99352, USA. wendy.shaw@pnnl.gov simone.raugei@pnnl.gov.)
Abstract	Electrocatalysts for $H_{2}$ production are envisioned to play an important role in renewable energy utilization systems. Nickel-based catalysts featuring pendant amines functioning as proton relays in the second coordination sphere of the metal center have led to catalysts achieving turnover frequencies as high as $10^{7}$ $s^{−1}$ for $H_{2}$ production. The fastest rates are observed when water is present in solution, with rates up to $10^{3}$ times faster than those found in dry solvent. The focus of this paper is to provide mechanistic insight into the unexpected enhancement due to water. Addition of $H_{2}$ to $[Ni(P^{Cy}_{2}N^{R′}_{2})_{2}]^{2+}$ was previously shown to give three isomers of a Ni(0) product with two protonated amines, where the N–H can be endo or exo to the Ni. By investigating the deprotonation of these two N-protonated Ni(0) intermediates resulting from the addition of $H_{2}$ to $[Ni(P^{Cy}_{2}N^{R′}_{2})_{2}]^{2+},$ we observe by NMR spectroscopy studies an enhancement in the rate of deprotonation for protons positioned on the pendant amine next to the metal (endo) vs. protons that are positioned away from the metal (exo). Computational studies suggest that for smaller bases, the desolvation energy of the exogenous base is the primary contribution limiting the rate of endo deprotonation, while steric accessibility and facile proton movement also contribute. For more bulky bases, steric accessibility can play the dominant role. The significant reduction in these barriers observed in the presence of water has important implications for disfavoring less productive catalytic pathways and increasing catalytic rates.
ISSN	14779226
Issue Number	24
Volume Number	44
e-ISSN	13645447
Journal	Dalton Trans.
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2015-06-28
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Amines Chemistry Coordination Complexes Hydrogen Nickel Protons Water Biomimetics Catalysis Isomerism Magnetic Resonance Spectroscopy Models, Molecular Oxidation-Reduction Journal Article Research Support, U.S. Gov't, Non-P.H.S.
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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