Molecular Au(I) complexes in the photosensitized photocatalytic CO 2 reduction reaction
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Research Letter
Molecular Au(I) complexes in the photosensitized photocatalytic CO2 reduction reaction Shakeyia Davis and Dinesh Nugegoda , Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA Joshua Tropp and Jason D. Azoulay, School of Polymer Science and Engineering, University of Southern Mississippi, Hattiesburg, MS 39406, USA Jared H. Delcamp , Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA Address all correspondence to Jared H. Delcamp at [email protected] (Received 28 January 2020; accepted 18 March 2020)
Abstract Five Au complexes are evaluated for the reduction reaction of CO2 via cyclic voltammetry and in a photocatalytic system. Electrochemically, the complexes were all evaluated for pre-association with CO2 prior to electrochemical reduction and for thermodynamic favorability for CO2 reduction in photocatalytic systems. The complexes were evaluated in photocatalytic reactions using an Ir-based photosensitizer and a sacrificial electron donor for the conversion of CO2 to CO. Au-complex counterion effects on the photocatalytic reaction were analyzed by varying weakly coordinating counterions with significant performance changes noted. At low Au-complex concentrations, a high TON value of 700 was observed.
Introduction The solar-driven conversion of CO2 to a fuel is an attractive process to meet growing energy demands. Au-based heterogeneous and multinuclear homogeneous Au catalysts are well known in the literature to drive this process.[1–5] While these complex systems are interesting, studying mononuclear homogeneous systems can be informative, readily tunable, and simpler to understand. As such, we sought to probe the behavior of four mononuclear Au complexes and one dinuclear Au complex in the catalytic photosensitized CO2 reduction reaction driven by simulated sunlight (Fig. 1). The five Au complexes selected for catalysis studies are readily available commercially (Fig. 1). Triphenylphosphine complexes 1 and 2 differ in the anionic ligand as either a bis(trifluoromethanesulfonyl)imide (TFSI) or a chloride allowing for the comparison of a weakly coordinating TFSI counterion with a more strongly coordinating chloride ion. Complexes 2, 3, and 5 differ in the neutral ligand (L) on the L-Au-Cl complexes studied, which allows for the comparison of triphenylphosphine (TPP, complex 2), tri-o-tolylphosphine (TTP, complex 5), and 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene as an N-heterocyclic carbene (NHC, complex 3). Finally, a comparison of the mononuclear complex 2 is possible with dinuclear complex 4, which has two diphenylphosphine ligated Au atoms linked by a methylene bridge. Herein, the Au-complex reduction potentials are determined through cyclic voltammetry analysis under argon and CO2 to ensure favorable energetics for the photocatalytic system using an iridium photosensitizer (Ir(ppy)3, where ppy is 2-phenylpyridine). The complexes are also evaluated within a photocatalytic reaction
with a sacrificial
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