Electrocatalytic oxidation of formate by [Ni(PR 2NR′ 2)2(CH3CN)] 2+ complexes

Brandon R. Galan, Julia Schöffel, John Linehan, Candace Seu, Aaron Appel, John Roberts, Monte Helm, Uriah J. Kilgore, Jenny Y. Yang, Daniel L DuBois, Clifford P. Kubiak

Research output: Contribution to journalArticle

72 Citations (Scopus)

Abstract

[Ni(PR 2NR′ 2) 2(CH3CN)]2+ complexes with R = Ph, R′ = 4-MeOPh or R = Cy, R′ = Ph, and a mixed-ligand [Ni(PR 2NR′ 2)(PR′′ 2NR′2)(CH3CN)]2+ with R = Cy, R′ = Ph, R′′ = Ph, have been synthesized and characterized by single-crystal X-ray crystallography. These and previously reported complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO2, protons, and electrons, with rates that are first-order in catalyst and formate at formate concentrations below ∼0.04 M (34 equiv). At concentrations above ∼0.06 M formate (52 equiv), catalytic rates become nearly independent of formate concentration. For the catalysts studied, maximum observed turnover frequencies vary from -1 at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. These catalysts are the only base-metal electrocatalysts as well as the only homogeneous electrocatalysts reported to date for the oxidation of formate. An acetate complex demonstrating an η1- OC(O)CH3 binding mode to nickel has also been synthesized and characterized by single-crystal X-ray crystallography. Based on this structure and the electrochemical and spectroscopic data, a mechanistic scheme for electrocatalytic formate oxidation is proposed which involves formate binding followed by a rate-limiting proton and two-electron transfer step accompanied by CO2 liberation. The pendant amines have been demonstrated to be essential for electrocatalysis, as no activity toward formate oxidation was observed for the similar [Ni(depe)2]2+ (depe = 1,2-bis(diethylphosphino)ethane) complex.

Original languageEnglish
Pages (from-to)12767-12779
Number of pages13
JournalJournal of the American Chemical Society
Volume133
Issue number32
DOIs
Publication statusPublished - Aug 17 2011

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formic acid
Electrocatalysts
Oxidation
Catalysts
X ray crystallography
Protons
Single crystals
Electrocatalysis
Electrons
X Ray Crystallography
Ethane
Amines
Thermodynamic properties
Ligands
Nickel

ASJC Scopus subject areas

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

Cite this

Electrocatalytic oxidation of formate by [Ni(PR 2NR′ 2)2(CH3CN)] 2+ complexes. / Galan, Brandon R.; Schöffel, Julia; Linehan, John; Seu, Candace; Appel, Aaron; Roberts, John; Helm, Monte; Kilgore, Uriah J.; Yang, Jenny Y.; DuBois, Daniel L; Kubiak, Clifford P.

In: Journal of the American Chemical Society, Vol. 133, No. 32, 17.08.2011, p. 12767-12779.

Research output: Contribution to journalArticle

Galan, Brandon R. ; Schöffel, Julia ; Linehan, John ; Seu, Candace ; Appel, Aaron ; Roberts, John ; Helm, Monte ; Kilgore, Uriah J. ; Yang, Jenny Y. ; DuBois, Daniel L ; Kubiak, Clifford P. / Electrocatalytic oxidation of formate by [Ni(PR 2NR′ 2)2(CH3CN)] 2+ complexes. In: Journal of the American Chemical Society. 2011 ; Vol. 133, No. 32. pp. 12767-12779.
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T1 - Electrocatalytic oxidation of formate by [Ni(PR 2NR′ 2)2(CH3CN)] 2+ complexes

AU - Galan, Brandon R.

AU - Schöffel, Julia

AU - Linehan, John

AU - Seu, Candace

AU - Appel, Aaron

AU - Roberts, John

AU - Helm, Monte

AU - Kilgore, Uriah J.

AU - Yang, Jenny Y.

AU - DuBois, Daniel L

AU - Kubiak, Clifford P.

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AB - [Ni(PR 2NR′ 2) 2(CH3CN)]2+ complexes with R = Ph, R′ = 4-MeOPh or R = Cy, R′ = Ph, and a mixed-ligand [Ni(PR 2NR′ 2)(PR′′ 2NR′2)(CH3CN)]2+ with R = Cy, R′ = Ph, R′′ = Ph, have been synthesized and characterized by single-crystal X-ray crystallography. These and previously reported complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO2, protons, and electrons, with rates that are first-order in catalyst and formate at formate concentrations below ∼0.04 M (34 equiv). At concentrations above ∼0.06 M formate (52 equiv), catalytic rates become nearly independent of formate concentration. For the catalysts studied, maximum observed turnover frequencies vary from -1 at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. These catalysts are the only base-metal electrocatalysts as well as the only homogeneous electrocatalysts reported to date for the oxidation of formate. An acetate complex demonstrating an η1- OC(O)CH3 binding mode to nickel has also been synthesized and characterized by single-crystal X-ray crystallography. Based on this structure and the electrochemical and spectroscopic data, a mechanistic scheme for electrocatalytic formate oxidation is proposed which involves formate binding followed by a rate-limiting proton and two-electron transfer step accompanied by CO2 liberation. The pendant amines have been demonstrated to be essential for electrocatalysis, as no activity toward formate oxidation was observed for the similar [Ni(depe)2]2+ (depe = 1,2-bis(diethylphosphino)ethane) complex.

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