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Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
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2016 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 42, p. 14870-14880Article in journal (Refereed) Published
Abstract [en]

A series of Ru-II polypyridyl complexes of the structural design [Ru-II(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, [Ru-II(tpy)(6-mbpy)(CH3CN)](2+) (trans-[3](2+); 6-mbpy= 6-methyl- 2,2'-bipyridine) and [Ru-II(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.

Place, publisher, year, edition, pages
2016. Vol. 22, no 42, p. 14870-14880
Keywords [en]
carbon dioxide, electrocatalysis, ligand design, ruthenium, steric hindrance
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-307274DOI: 10.1002/chem.201601612ISI: 000384806700002PubMedID: 27459316OAI: oai:DiVA.org:uu-307274DiVA, id: diva2:1046372
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg FoundationWenner-Gren FoundationsAvailable from: 2016-11-14 Created: 2016-11-11 Last updated: 2017-11-29Bibliographically approved

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