The Trans Effect in Electrocatalytic CO 2 Reduction: Mechanistic Studies of Asymmetric Ruthenium Pyridyl-Carbene Catalysts

Sergio Gonell, Marsha D. Massey, Ian P. Moseley, Cynthia K. Schauer, James Muckerman, Alexander J.M. Miller

Research output: Contribution to journalArticle

Abstract

A comprehensive mechanistic study of electrocatalytic CO 2 reduction by ruthenium 2,2′:6′,2″-terpyridine (tpy) pyridyl-carbene catalysts reveals the importance of stereochemical control to locate the strongly donating N-heterocyclic carbene ligand trans to the site of CO 2 activation. Computational studies were undertaken to predict the most stable isomer for a range of reasonable intermediates in CO 2 reduction, suggesting that the ligand trans to the reaction site plays a key role in dictating the energetic profile of the catalytic reaction. A new isomer of [Ru(tpy)(Mebim-py)(NCCH 3 )] 2+ (Mebim-py is 1-methylbenzimidazol-2-ylidene-3-(2′-pyridine)) and both isomers of the catalytic intermediate [Ru(tpy)(Mebim-py)(CO)] 2+ were synthesized and characterized. Experimental studies demonstrate that both isomeric precatalysts facilitate electroreduction of CO 2 to CO in 95/5 MeCN/H 2 O with high activity and high selectivity. Cyclic voltammetry, infrared spectroelectrochemistry, and NMR spectroscopy studies provide a detailed mechanistic picture demonstrating an essential isomerization step in which the N-trans catalyst converts in situ to the C-trans variant. Insight into molecular electrocatalyst design principles emerge from this study. First, the use of an asymmetric ligand that places a strongly electron-donating ligand trans to the site of CO 2 binding and activation is critical to high activity. Second, stereochemical control to maintain the desired isomer structure during catalysis is critical to performance. Finally, pairing the strongly donating pyridyl-carbene ligand with the redox-active tpy ligand proves to be useful in boosting activity without sacrificing overpotential. These design principles are considered in the context of surface-immobilized electrocatalysis.

Original languageEnglish
Pages (from-to)6658-6671
Number of pages14
JournalJournal of the American Chemical Society
Volume141
Issue number16
DOIs
Publication statusPublished - Apr 24 2019

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Ruthenium
Carbon Monoxide
Ligands
Isomers
Catalysts
Chemical activation
Spectroelectrochemistry
Electrocatalysis
Electrocatalysts
Isomerization
Pyridine
Catalysis
Nuclear magnetic resonance spectroscopy
Cyclic voltammetry
carbene
Oxidation-Reduction
Magnetic Resonance Spectroscopy
Infrared radiation
Electrons

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

The Trans Effect in Electrocatalytic CO 2 Reduction : Mechanistic Studies of Asymmetric Ruthenium Pyridyl-Carbene Catalysts. / Gonell, Sergio; Massey, Marsha D.; Moseley, Ian P.; Schauer, Cynthia K.; Muckerman, James; Miller, Alexander J.M.

In: Journal of the American Chemical Society, Vol. 141, No. 16, 24.04.2019, p. 6658-6671.

Research output: Contribution to journalArticle

Gonell, Sergio ; Massey, Marsha D. ; Moseley, Ian P. ; Schauer, Cynthia K. ; Muckerman, James ; Miller, Alexander J.M. / The Trans Effect in Electrocatalytic CO 2 Reduction : Mechanistic Studies of Asymmetric Ruthenium Pyridyl-Carbene Catalysts. In: Journal of the American Chemical Society. 2019 ; Vol. 141, No. 16. pp. 6658-6671.
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