Metalloenzyme mimic: diironhexacarbonyl cluster coupled to redox-active 4-mercapto-1,8-naphthalic anhydride ligands
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Metalloenzyme mimic: diironhexacarbonyl cluster coupled to redox‑active 4‑mercapto‑1,8‑naphthalic anhydride ligands Charles A. Mebi1 · Jordan H. Labrecque2 · Andrew A. Williams3 Received: 29 April 2020 / Accepted: 16 June 2020 © Springer Nature Switzerland AG 2020
Abstract The non-innocent redox-active ligand, 4-mercapto-1,8-naphthalic anhydride (HS-NAH), has been used in the design and synthesis of a diironhexacarbonyl complex, [μ-(S-NAH)2Fe2(CO)6]. [μ-(S-NAH)2Fe2(CO)6] has been characterized by spectroscopic methods and cyclic voltammetry. Infrared spectrum of [μ-(S-NAH)2Fe2(CO)6] displays peaks corresponding to terminal metal CO groups (2081, 2044, 2006 cm−1) and peaks assigned to C=O of the naphthalic anhydrides (1780, 1740 cm−1). Electrochemical measurements of [μ-(S-NAH)2Fe2(CO)6] feature redox events that are metal-based (irreversible, Epc: − 1.13 V, − 1.60 V vs Fc/Fc+) and naphthalic anhydride centered (partially chemically reversible, Epc: − 1.99 V; Epa: − 1.90 V vs Fc/Fc+). Cyclic voltammetric analysis of [μ-(S-NAH)2Fe2(CO)6] in the presence of acetic acid show that the complex mimics the active site of [Fe–Fe]-hydrogenase by catalyzing the electrochemical reduction of protons to hydrogen with an overpotential of − 0.67 V. The bi-functional model, [μ-(S-NAH)2Fe2(CO)6], exhibits electronic coupling with synergistic metal–ligand interactions leading to transformation of protons to molecular hydrogen.
Introduction In light of the environmental consequences associated with our dependence on fossil fuels, there is great and urgent need for clean and sustainable fuel options to meet growing energy demand. Of the available substitutes, hydrogen has emerged as a viable green alternative to gasoline as a transportation fuel. Hydrogen has a high energy density, and its use in fuel cells results in the formation of water as the only by-product [1–5]. Natural gas reforming is the current method used for industrial scale production of hydrogen. This is an important technology for near-term hydrogen Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11243-020-00410-y) contains supplementary material, which is available to authorized users. * Charles A. Mebi [email protected] 1
Department of Physical Sciences, College of Natural and Health Sciences, Arkansas Tech University, 1701 N. Boulder Ave., Russellville, AR 72801, USA
2
Present Address: Department of Chemistry, College of Natural Sciences, University of Texas, Austin, TX 78712, USA
3
Present Address: Science Department, Batesville High School, Batesville, AR 72501, USA
production [6]. However, this technology is dependent on non-renewable hydrocarbon that is a potent greenhouse gas. Current production of hydrogen from water, which is cheap and abundant, requires rare and expensive platinum as electrocatalyst [4]. In the search for cheaper and more efficient electrocatalyts for hydrogen production, researchers are inspired by nature, particularly by the metalloenzyme [Fe–Fe]-hydrogenase. [Fe–Fe]-hydr
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