Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H<sub>2</sub>

Liu, Tianbiao L.; Liu, Qian; O’Hagan, Molly; Hulley, Elliott B.; DuBois, Daniel L.; Bullock, R. Morris

doi:10.1021/om501289f

Cited by 38 publications

(34 citation statements)

References 87 publications

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“…The NOESY spectrum at –40 °C (Fig. S18†) shows an exchange correlation of the FeH only with the NH resonance of the syn (boat) isomer, presumably occurring through an unobserved Fe(H 2 ) + intermediate 54,68…”

Section: Resultsmentioning

confidence: 99%

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

et al. 2019

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Section: Resultsmentioning

confidence: 99%

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

et al. 2019

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“…Modification of the basicity of the pendant amine led to the ability to control the energy for heterolytic cleavage [95]. Sterically bulky substituents to block exogenous base was only one part of the solution to ineffective catalysis in the Cp derivative in scheme 19; the acidity of the Fe-H 2 complex must be high enough for deprotonation.…”

Section: Scheme 19 (Online Version In Colour)mentioning

confidence: 99%

“…This H•••H separation is much larger than the H-H distance found in dihydrogen complexes. For example, an H-H distance of about 0.94Å was estimated for the dihydrogen ligand of [Cp C 6 F 5 Fe(P t-Bu 2 N Bn 2 )(H 2 )] + on the basis of the J(HD) coupling constant in the 1 H NMR spectrum of the HD complex [94]; a series of related Fe(H 2 ) complexes have also been compared using NMR spectroscopic measurements [95]. This study of heterolytic cleavage by an iron complex with a pendant amine provides a model for the heterolytic cleavage of H 2 in the more complex [FeFe]-hydrogenase in nature, where obtaining reliable structural data of enzymes is often difficult.…”

Section: Scheme 19 (Online Version In Colour)mentioning

confidence: 99%

Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes

Bullock

Chambers

2017

Phil. Trans. R. Soc. A.

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This perspective examines frustrated Lewis pairs (FLPs) in the context of heterolytic cleavage of H by transition metal complexes, with an emphasis on molecular complexes bearing an intramolecular Lewis base. FLPs have traditionally been associated with main group compounds, yet many reactions of transition metal complexes support a broader classification of FLPs that includes certain types of transition metal complexes with reactivity resembling main group-based FLPs. This article surveys transition metal complexes that heterolytically cleave H, which vary in the degree that the Lewis pairs within these systems interact. Many of the examples include complexes bearing a pendant amine functioning as the base with the metal functioning as the hydride acceptor. Consideration of transition metal compounds in the context of FLPs can inspire new innovations and improvements in transition metal catalysis.This article is part of the themed issue 'Frustrated Lewis pair chemistry'.

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“…Eq. 4 has successfully been applied to identify and optimize electrocatalysts for H 2 evolution (26,(31)(32)(33)(34)(35)(36)(37)(38) and H 2 oxidation (31)(32)(33)(34)(39)(40)(41)(42), and to achieve reversible reactivity (43,44).The relationship between pK a , hydricity, and H 2 evolution in acetonitrile is quantitatively depicted in Fig. 2A.…”

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Directing the reactivity of metal hydrides for selective CO ₂ reduction

Ceballos

Yang

2018

Proc. Natl. Acad. Sci. U.S.A.

102

119

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A critical challenge in electrocatalytic CO 2 reduction to renewable fuels is product selectivity. Desirable products of CO 2 reduction require proton equivalents, but key catalytic intermediates can also be competent for direct proton reduction to H 2 . Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO 2 reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H + and CO 2 to generate a thermodynamic product diagram, which outlines the free energy of product formation as a function of proton activity and hydricity (ΔG H− ), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO 2 reduction is favorable and H + reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe) 2 ](PF 6 ) 2 as a potential catalyst, because the corresponding hydride [HPt(dmpe) 2 ] + has the correct hydricity to access the region where selective CO 2 reduction is possible. We validate our choice experimentally; [Pt(dmpe) 2 ](PF 6 ) 2 is a highly selective electrocatalyst for CO 2 reduction to formate (>90% Faradaic efficiency) at an overpotential of less than 100 mV in acetonitrile with no evidence of catalyst degradation after electrolysis. Our report of a selective catalyst for CO 2 reduction illustrates how our thermodynamic diagrams can guide selective and efficient catalyst discovery. electrocatalysis | CO 2 reduction | solar fuel | formate production | hydride T he emerging availability of inexpensive renewable electricity has motivated interest in using electrolytic methods to generate sustainable fuels. Electrocatalytic CO 2 reduction provides an entry to carbon-neutral fuels, but product selectivity remains a significant challenge (1, 2). Nearly all reductive reactions of interest involve protons as well as electrons, introducing the complication of direct proton reduction to H 2 under electrolytic conditions. Diversion of electron equivalents into proton reduction results in lower Faradaic efficiency for the desired CO 2 reduction reaction. Various strategies to inhibit or suppress H 2 evolution for heterogeneous (3-7) and homogeneous (8,9) catalysts have been explored.To understand the factors that determine selectivity between CO 2 and H + reduction, we have been investigating the reactivity of metal hydrides. Selectivity for formate production is particularly challenging because metal hydride intermediates are common to both reaction pathways (Fig. 1). As a result, very few heterogeneous (10-13) or homogeneous (14-16) catalysts have been reported with high (>90%) Faradaic efficiency for formate production. Understanding the reactivity of metal hydrides is key to controlling the bifurcating reaction pathways that ultimately determine selectivity. Most selective catalysts for CO 2 reduction utilize kinetic inhibition (or a high-...

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Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H₂

Abstract: The synthesis and spectroscopic characterization of Cp C 5 F 4 N Fe(P tBu 2 N Bn 2 )Cl, [3-Cl] (where C 5 F 4 N is a tetrafluoropyridyl substituent and P tBu 2 N Bn 2 = 1,5-dibenzyl-3,7-di(tert-butyl)-1,5-diaza-3,7-diphosphacyclooctane), are reported. Complex 3-Cl and [Cp C 5

Cited by 38 publications

References 87 publications

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes

Directing the reactivity of metal hydrides for selective CO ₂ reduction

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Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H2

Abstract: The synthesis and spectroscopic characterization of Cp C 5 F 4 N Fe(P tBu 2 N Bn 2 )Cl, [3-Cl] (where C 5 F 4 N is a tetrafluoropyridyl substituent and P tBu 2 N Bn 2 = 1,5-dibenzyl-3,7-di(tert-butyl)-1,5-diaza-3,7-diphosphacyclooctane), are reported. Complex 3-Cl and [Cp C 5

Cited by 38 publications

References 87 publications

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

Anion control of tautomeric equilibria: Fe–H vs. N–H influenced by NH⋯F hydrogen bonding

Frustration across the periodic table: heterolytic cleavage of dihydrogen by metal complexes

Directing the reactivity of metal hydrides for selective CO 2 reduction

Contact Info

Product

Resources

About

Iron Complexes Bearing Diphosphine Ligands with Positioned Pendant Amines as Electrocatalysts for the Oxidation of H₂

Directing the reactivity of metal hydrides for selective CO ₂ reduction