Synthesis, Properties, and Electrochemical Proton Reduction of a Homoleptic Tetrathiolato Ni-Site Model of [NiFe]-Hydrogenase
Benjamin A. Yosen, Amelia G. Reid, Phan T. Truong, Tiara Hinton, Indranil Chakraborty, Marilyn M. Olmstead, Timothy L. Stemmler, Todd C. Harrop
TL;DR
This paper reports the synthesis and electrochemical evaluation of a nickel-based model compound for [NiFe]-hydrogenase, showing modest hydrogen production activity.
Contribution
A tetrathiolato Ni2+ complex is shown to act as a modest electrocatalyst for the hydrogen evolution reaction.
Findings
The compound (Et4N)2[Ni(S-p-CF3–Ph)4] exhibits a distorted tetrahedral geometry confirmed by X-ray crystallography.
The complex shows electrochemical HER activity with a turnover frequency of 14.5 ± 3.6 s–1 and an overpotential of 0.72 ± 0.02 V.
An ECCE-type mechanism is proposed for the HER based on experiments and DFT computations.
Abstract
[NiFe]-hydrogenase enzymes process H2 at a nonplanar tetracysteinato-Ni site, the sole participator in proton binding/redox chemistry during turnover. With the objective of assessing whether a simple tetrahedral/tetrathiolato-Ni2+ core could promote H2 evolution reaction (HER), we synthesized (Et4N)2[Ni(S-p-CF3–Ph)4] (1) employing para-trifluoromethylbenzenethiolate (−S-p-CF3–Ph) as a Ni-site analog of [NiFe]-hydrogenase. Spectroscopic measurements and X-ray crystallography confirm the distorted tetrahedral geometry of 1. Dissolution of 1 results in partial thiolate dissociation and formation of S,S-bridged complexes such as (Et4N)2[Ni2(S-p-CF3–Ph)6] (3) among other ill-defined species. Dissociation is further accelerated in the presence of Brønsted acids, complicating the assessment of 1 for proton reduction. However, this dissociation/proton instability is suppressed in the presence…
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Taxonomy
TopicsMetalloenzymes and iron-sulfur proteins · Hydrogen Storage and Materials · Electrocatalysts for Energy Conversion