Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

Johnson, B A and Agarwala, H and White, T A and Mijangos, E and Maji, Somnath and Ott, S (2016) Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects. Chemistry - A European Journal, 22 (42). pp. 14870-14880. ISSN 0947-6539

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A series of RuII polypyridyl complexes of the structural design [RuII(R−tpy)(NN)(CH3CN)]2+ (R−tpy=2,2′:6′,2′′-terpyridine (R=H) or 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine (R=tBu); NN=2,2′-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [RuII(tpy)(6-mbpy)(CH3CN)]2+ (trans-[3]2+; 6-mbpy=6-methyl-2,2′-bipyridine) and [RuII(tBu−tpy)(6-mbpy)(CH3CN)]2+ (trans-[4]2+), in which the methyl group of the 6-mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.

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IITH Creators:
IITH CreatorsORCiD
Maji, Somnathhttp://orcid.org/0000-0001-6047-1339
Item Type: Article
Additional Information: As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. LINK - http://onlinelibrary.wiley.com/store/10.1002/chem.201601612/asset/supinfo/chem201601612-sup-0001-misc_information.pdf?v=1&s=23cf8102d16cc0383571e6cd2bcf05756e958c65
Uncontrolled Keywords: carbon dioxide;electrocatalysis;ligand design;ruthenium;steric hindrance
Subjects: Chemistry
Divisions: Department of Chemistry
Depositing User: Team Library
Date Deposited: 01 Aug 2016 05:14
Last Modified: 09 Oct 2017 09:30
URI: http://raiith.iith.ac.in/id/eprint/2587
Publisher URL: https://dx.doi.org/10.1002/chem.201601612
OA policy: http://www.sherpa.ac.uk/romeo/issn/0947-6539/
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