Walaijai, Khanittha, Cavill, Stuart Alan orcid.org/0000-0002-1359-4958, Whitwood, Adrian C. et al. (2 more authors) (2020) Electrocatalytic proton reduction by a cobalt(III) hydride complex with phosphinopyridine PN ligands. Inorganic Chemistry. ISSN 0020-1669
Abstract
Cobalt complexes with 2-(diisopropylphosphinomethyl)pyridine (PN) ligands have been synthesized with the aim of demonstrating electrocatalytic proton reduction to dihydrogen with a well-defined hydride complex of an Earth-abundant metal. Reactions of simple cobalt precursors with 2-(diisopropylphosphino-methyl)pyridine, (PN) yield [CoII(PN)2(MeCN)][BF4]2 1, [CoIII(PN)2(H)(MeCN)][PF6]2 2 and [CoIII(PN)2(H)(Cl)][PF6] 3. Complexes 1 and 3 have been characterized crystallographically. Unusually for a bidentate PN ligand, all three exhibit geometries with mutually trans phosphorus and nitrogen ligands. Complex 1 exhibits a distorted square-pyramidal geometry with an axial MeCN ligand in a low-spin electronic state. In complexes 2 and 3, the PN ligands lie in a plane leaving the hydride trans to MeCN or chloride, respectively. The redox behavior of the three complexes has been studied by cyclic voltammetry at variable scan rates and by spectroelectrochemistry. A catalytic wave is observed in the presence of trifluoroacetic acid (TFA) at an applied potential close to the Co(II/I) couple of 1. Bulk electrolysis of 1, 2 or 3 at a potential of –1.4 V in the presence of TFA yields H2 with Faradaic yields close to 100%. Foot-of-the-wave analysis allows calculation of kcat values of 860 and 1560 M-1 s-1 for 1 and 2 measured at 0.025 and 0.030 M TFA, respectively. The catalytic performance of 1 and 2 is compared to those of related catalysts by means of Tafel plots. A catalytic mechanism is proposed in which the pyridine moiety of a PN ligand acts as a pendant proton donor following opening of the chelate ring.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details. |
Dates: |
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Institution: | The University of York |
Academic Units: | The University of York > Faculty of Sciences (York) > Chemistry (York) The University of York > Faculty of Sciences (York) > Physics (York) |
Depositing User: | Pure (York) |
Date Deposited: | 30 Nov 2020 13:10 |
Last Modified: | 11 Jan 2025 00:07 |
Published Version: | https://doi.org/10.1021/acs.inorgchem.0c02505 |
Status: | Published online |
Refereed: | Yes |
Identification Number: | 10.1021/acs.inorgchem.0c02505 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:164825 |
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Filename: Co_hydride_PN_complexes_and_electrocatalytic_proton_reduction_revised_5_nov_changes_accepted.pdf
Description: Co hydride PN complexes and electrocatalytic proton reduction revised 5 nov changes accepted