Directing the Reactivity of [HFe4N(CO)12]− toward H+ or CO2 Reduction by Understanding the Electrocatalytic Mechanism

Rail, M. Diego; Berben, Louise A.

doi:10.1021/ja208312t

Cited by 111 publications

(128 citation statements)

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“…31–35 The pathway to CO and CH 4 formation is believed to involve the addition of H to the O atom of CO 2 , whereas the pathway to HCOO − formation is believed to involve the addition of H to the C atom of CO 2 . 36,37 In this context, we tested whether wild type nitrogenase could reduce CO 2 to HCOO − , a reaction that had not been reported before.…”

Section: Resultsmentioning

confidence: 99%

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

et al. 2016

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The reduction of N2 to NH3 by Mo-dependent nitrogenase at its active-site metal cluster FeMo-cofactor utilizes reductive elimination (re) of Fe-bound hydrides with obligatory loss of H2 to activate the enzyme for binding/reduction of N2. Earlier work showed that wild type nitrogenase and a nitrogenase having amino acid substitutions in the MoFe protein near FeMo-cofactor can catalytically reduce CO2 by 2 or 8 electrons/protons to carbon monoxide (CO) and methane (CH4) at low rates. Here, it is demonstrated that nitrogenase preferentially reduces CO2 by 2 electrons/protons to formate (HCOO−) at rates >10 times higher than rates of CO2 reduction to yield CO and CH4. Quantum mechanical (QM) calculations on the doubly-reduced FeMo-cofactor with a Fe-bound hydride and S-bound proton (E2(2H) state) favor a direct reaction of CO2 with the hydride (‘direct hydride transfer’ reaction pathway), with facile hydride transfer to CO2 yielding formate. In contrast, a significant barrier is observed for reaction of Fe-bound CO2 with the hydride (‘associative’ reaction pathway), which leads to CO and CH4. Remarkably, in the direct hydride transfer pathway, the Fe-H behaves as a hydridic hydrogen, whereas in the associative pathway it acts as a protic hydrogen. MoFe proteins having amino acid substitutions near FeMo-cofactor (α-70Val→Ala, α -195His→Gln) are found to significantly alter the distribution of products between formate and CO/CH4.

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Section: Resultsmentioning

confidence: 99%

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

et al. 2016

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“…9,23,24 Mechanistic insights have been gained recently too with Re, [28][29][30] Mn 31,32 and Ni 33-36 based catalysts through electrochemical and spectroscopic analysis, and quantum chemistry calculations. The reduction of carbon dioxide into formate has been more rarely observed using molecular catalysts, in electrochemical conditions with Fe, Ni, Co, Ru, Rh or Ir based catalysts [37][38][39][40][41][42][43][44][45][46][47][48][49] (see also tables 2 and 3 in reference 7) and in photochemical conditions 13,14,[50][51][52][53] with Re, Ru, Ir main-2 ly and very recently Mn complexes. 53 Mechanistic studies have accordingly been scarce.…”

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confidence: 99%

“…53 Mechanistic studies have accordingly been scarce. In some cases, formate is deemed to result from the insertion of CO 2 by a metalhydride donor intermediate (before or after the hydride is further reduced), as found with Re, Ru and Ir 46,50,51 as well as with Fe complexes, 45,47 but this may not be always the case and the active metal based catalyst may bind to CO 2 through one of the oxygen atoms without intermediacy of an hydride species. 41 We have discovered that two complexes [Co II (L)](ClO 4 ) 2 and [Fe III (L)(Cl) 2 ](ClO 4 ) bearing a pentadendate N5 ligand (Scheme 1) to CO and HCOOH respectively, in electrochemical and Scheme 1.…”

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confidence: 99%

“…47 Finally, a recent example related to an iron cluster complex gave CO 2 -to-HCOOH conversion in acetonitrile at comparable overpotential than 2, the formic acid being identified by 13 C NMR spectroscopy. 45 Going to more expensive metals, an example concerns the use an iridium pincer immobilized at the surface of a carbon electrode and has led to high selectivity and activity towards CO 2 -to-HCOOH conversion in water at overpotentials larger than 510 mV. 58 Ru(bpy) 2 (CO) 2 2+ (bpy = 2,2'-bipyridine) also furnishes formic acid during electrolysis at mercury pool with current density of ca.…”

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confidence: 99%

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Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO₂ with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center

et al. 2015

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Molecular catalysis of carbon dioxide reduction using earth-abundant metal complexes as catalysts is a key challenge related to the production of useful products--the "solar fuels"--in which solar energy would be stored. A direct approach using sunlight energy as well as an indirect approach where sunlight is first converted into electricity could be used. A Co(II) complex and a Fe(III) complex, both bearing the same pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), were synthesized, and their catalytic activity toward CO2 reduction was investigated. Carbon monoxide was formed with the cobalt complex, while formic acid was obtained with the iron-based catalyst, thus showing that the catalysis product can be switched by changing the metal center. Selective CO2 reduction occurs under electrochemical conditions as well as photochemical conditions when using a photosensitizer under visible light excitation (λ > 460 nm, solvent acetonitrile) with the Co catalyst. In the case of the Fe catalyst, selective HCOOH production occurs at low overpotential. Sustained catalytic activity over long periods of time and high turnover numbers were observed in both cases. A catalytic mechanism is suggested on the basis of experimental results and preliminary quantum chemistry calculations.

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“…A variety of approaches to CO 2 reduction to formate have been explored including hydrogenation [48], hydroboration [49], hydrosilylation [50], and electrochemical reduction [51][52][53][54][55][56]. Hydrogenation and electrochemical reduction are potentially economically viable.…”

Section: Co 2 Reduction To Formate By Ir Pincer Complexesmentioning

confidence: 99%

Electrocatalytic Reduction of Carbon Dioxide: Let the Molecules Do the Work

et al. 2014

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This review summarizes the development of electrochemical CO 2 reduction catalysts in the UNC Energy Frontier Research Center for Solar Fuels. Two strategies for converting CO 2 to CO or formate have been explored. In one, polypyridyl complexes of Ru(II) have been used to reduce CO 2 to CO in acetonitrile and in acetonitrile/water mixtures. In the absence of CO 2 water is reduced to H 2 by these complexes. With added weak acids in acetonitrile with added water and CO 2 , reduction to syngas mixtures of CO and H 2 is observed. A single polypyridyl complex of Ru(II) has been shown to be both a catalyst for water oxidation and CO 2 reduction in an electrochemical cell for CO 2 splitting into CO and O 2 . In parallel, Ir pincer catalysts have been shown to act as selective electrocatalysts for reducing CO 2 to formate in acetonitrile with added water and in pure water without competition from electrocatalytic H 2 production. Details of the catalytic mechanisms of each have also been investigated.The world's energy future is being driven by increased demand which is currently met by increasing use of fossil fuels with their associated environmental impact through the greenhouse gas effect [1]. With technologies that evolve to become cost effective, renewable energy is the appealing energy source of the future with the sun the ultimate energy source. However, large-scale use of solar energy requires large land areas and a vast energy storage capability for nighttime and on-demand utilization. Natural photosynthesis is appealing with energy conversion through stored biomass but, with typical solar efficiencies of B1 %, is impractical as a source for the high energy densities required to power urban centers and industrial complexes. A long-term solution is potentially available based on ''artificial photosynthesis'' with solar fuels the product, water splitting into H 2 and O 2 or reduction of CO 2 to a carbon fuel or carbon fuel precursor [2]. Solar-driven reduction of CO 2 by water occurs in green plants and photosynthetic bacteria and is an inspiration for the development of an artificial photosynthesis-based equivalent. Given the impressive efficiencies reached with current semiconductor technology for photovotaic devices, far higher efficiencies should be reachable in artificial photosynthesis compared to natural photosynthesis with a target of [10 % being a reasonable goal. The products of artificial photosynthesis are so-called solar fuels, highenergy density molecules with solar energy stored in chemical bonds. As noted above, target reactions are water splitting into hydrogen and oxygen, and reduction of CO 2 to CO, formic acid, methanol or other reduced forms of carbon, with hydrocarbons especially attractive because

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Directing the Reactivity of [HFe₄N(CO)₁₂]⁻ toward H⁺ or CO₂ Reduction by Understanding the Electrocatalytic Mechanism

Cited by 111 publications

References 20 publications

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO₂ with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center

Electrocatalytic Reduction of Carbon Dioxide: Let the Molecules Do the Work

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Directing the Reactivity of [HFe4N(CO)12]− toward H+ or CO2 Reduction by Understanding the Electrocatalytic Mechanism

Cited by 111 publications

References 20 publications

CO2 Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

CO2 Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center

Electrocatalytic Reduction of Carbon Dioxide: Let the Molecules Do the Work

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Directing the Reactivity of [HFe₄N(CO)₁₂]⁻ toward H⁺ or CO₂ Reduction by Understanding the Electrocatalytic Mechanism

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

CO₂ Reduction Catalyzed by Nitrogenase: Pathways to Formate, Carbon Monoxide, and Methane

Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO₂ with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center