Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe4S4 surrogates

Georgia R.F. Orton; Shishir Ghosh; Lucy Alker; Jagodish C. Sarker; David Pugh; Michael G. Richmond; František Hartl; Graeme Hogarth

doi:10.1039/d2dt00419d

Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe₄S₄ surrogates

Georgia R.F. Orton, Shishir Ghosh, Lucy Alker, Jagodish C. Sarker, David Pugh, Michael G. Richmond, František Hartl, Graeme Hogarth^*

^*Corresponding author for this work

Chemistry

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Abstract

[FeFe]-Ase biomimics containing a redox-active ferrocenyl diphosphine have been prepared and their ability to reduce protons and oxidise H₂ studied, including 1,1′-bis(diphenylphosphino)ferrocene (dppf) complexes Fe₂(CO)₄(μ-dppf)(μ-S(CH₂)_nS) (n = 2, edt; n = 3, pdt) and Fe₂(CO)₄(μ-dppf)(μ-SAr)₂ (Ar = Ph, p-tolyl, p-C₆H₄NH₂), together with the more electron-rich 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf) complex Fe₂(CO)₄(μ-dcpf)(μ-pdt). Crystallographic characterisation of four of these show similar overall structures, the diphosphine spanning an elongated Fe-Fe bond (ca. 2.6 Å), lying trans to one sulfur and cis to the second. In solution the diphosphine is flexible, as shown by VT NMR studies, suggesting that Fe₂⋯Fe distances of ca. 4.5-4.7 Å in the solid state vary in solution. Cyclic voltammetry, IR spectroelectrochemistry and DFT calculations have been used to develop a detailed picture of electronic and structural changes occurring upon oxidation. In MeCN, Fe₂(CO)₄(μ-dppf)(μ-pdt) shows two chemically reversible one-electron oxidations occurring sequentially at Fe₂ and Fc sites respectively. For other dppf complexes, reversibility of the first oxidation is poor, consistent with an irreversible structural change upon removal of an electron from the Fe₂ centre. In CH₂Cl₂, Fe₂(CO)₄(μ-dcpf)(μ-pdt) shows a quasi-reversible first oxidation together with subsequent oxidations suggesting that the generated cation has some stability but slowly rearranges. Both pdt complexes readily protonate upon addition of HBF₄·Et₂O to afford bridging-hydride cations, [Fe₂(CO)₄(μ-H)(μ-dcpf)(μ-pdt)]⁺, species which catalytically reduce protons to generate H₂. In the presence of pyridine, [Fe₂(CO)₄(μ-dppf)(μ-pdt)]²⁺ catalytically oxidises H₂ but none of the other complexes do this, probably resulting from the irreversible nature of their first oxidation. Mechanistic details of both proton reduction and H₂ oxidation have been studied by DFT allowing speculative reaction schemes to be developed.

Original language	English
Pages (from-to)	9748-9769
Number of pages	22
Journal	Dalton Transactions
Volume	51
Issue number	25
Early online date	6 Jun 2022
DOIs	https://doi.org/10.1039/d2dt00419d
Publication status	Published - 7 Jul 2022

Bibliographical note

Funding Information:
We thank the Commonwealth Scholarship Commission for the award of Commonwealth Scholarships (SG and JCS) and King's College London (GRFO) for PhD funding. GH thanks The Royal Society of Chemistry for an International Authors Grant which allowed this work to be developed during his visit to the University of North Texas and King's College London for funding. We thank Dr Nathan Patmore (University of Huddersfield) for some early IR-SEC on 1, Professor Katherine J. Holt (UCL) for the initial electrochemical study on 1, Dr Nathan Hollingsworth (ex-UCL) for part supervision of LA, and Kishan Muthu (KCL) for early attempts to prepare 2 while working under the supervision of GRFO. MGR acknowledges financial support from the Robert A. Welch Foundation (Grant B-1093-MGR). Computational resources through the High-Performance Computing Services and CASCaM at the University of North Texas are acknowledged. Dr David A. Hrovat is thanked for the generation of the spin density plots of B and 3C. The experimental work in Reading was conducted with the support from Spectroelectrochemistry Reading, a spinout company of the University.

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

ASJC Scopus subject areas

Inorganic Chemistry

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Orton, G. R. F., Ghosh, S., Alker, L., Sarker, J. C., Pugh, D., Richmond, M. G., Hartl, F., & Hogarth, G. (2022). Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe₄S₄ surrogates. Dalton Transactions, 51(25), 9748-9769. https://doi.org/10.1039/d2dt00419d

@article{cf2425aeb8bd4a6a9acd9da2285102e1,

title = "Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe4S4 surrogates",

abstract = "[FeFe]-Ase biomimics containing a redox-active ferrocenyl diphosphine have been prepared and their ability to reduce protons and oxidise H2 studied, including 1,1′-bis(diphenylphosphino)ferrocene (dppf) complexes Fe2(CO)4(μ-dppf)(μ-S(CH2)nS) (n = 2, edt; n = 3, pdt) and Fe2(CO)4(μ-dppf)(μ-SAr)2 (Ar = Ph, p-tolyl, p-C6H4NH2), together with the more electron-rich 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf) complex Fe2(CO)4(μ-dcpf)(μ-pdt). Crystallographic characterisation of four of these show similar overall structures, the diphosphine spanning an elongated Fe-Fe bond (ca. 2.6 {\AA}), lying trans to one sulfur and cis to the second. In solution the diphosphine is flexible, as shown by VT NMR studies, suggesting that Fe2⋯Fe distances of ca. 4.5-4.7 {\AA} in the solid state vary in solution. Cyclic voltammetry, IR spectroelectrochemistry and DFT calculations have been used to develop a detailed picture of electronic and structural changes occurring upon oxidation. In MeCN, Fe2(CO)4(μ-dppf)(μ-pdt) shows two chemically reversible one-electron oxidations occurring sequentially at Fe2 and Fc sites respectively. For other dppf complexes, reversibility of the first oxidation is poor, consistent with an irreversible structural change upon removal of an electron from the Fe2 centre. In CH2Cl2, Fe2(CO)4(μ-dcpf)(μ-pdt) shows a quasi-reversible first oxidation together with subsequent oxidations suggesting that the generated cation has some stability but slowly rearranges. Both pdt complexes readily protonate upon addition of HBF4·Et2O to afford bridging-hydride cations, [Fe2(CO)4(μ-H)(μ-dcpf)(μ-pdt)]+, species which catalytically reduce protons to generate H2. In the presence of pyridine, [Fe2(CO)4(μ-dppf)(μ-pdt)]2+ catalytically oxidises H2 but none of the other complexes do this, probably resulting from the irreversible nature of their first oxidation. Mechanistic details of both proton reduction and H2 oxidation have been studied by DFT allowing speculative reaction schemes to be developed.",

author = "Orton, {Georgia R.F.} and Shishir Ghosh and Lucy Alker and Sarker, {Jagodish C.} and David Pugh and Richmond, {Michael G.} and Franti{\v s}ek Hartl and Graeme Hogarth",

note = "Funding Information: We thank the Commonwealth Scholarship Commission for the award of Commonwealth Scholarships (SG and JCS) and King's College London (GRFO) for PhD funding. GH thanks The Royal Society of Chemistry for an International Authors Grant which allowed this work to be developed during his visit to the University of North Texas and King's College London for funding. We thank Dr Nathan Patmore (University of Huddersfield) for some early IR-SEC on 1, Professor Katherine J. Holt (UCL) for the initial electrochemical study on 1, Dr Nathan Hollingsworth (ex-UCL) for part supervision of LA, and Kishan Muthu (KCL) for early attempts to prepare 2 while working under the supervision of GRFO. MGR acknowledges financial support from the Robert A. Welch Foundation (Grant B-1093-MGR). Computational resources through the High-Performance Computing Services and CASCaM at the University of North Texas are acknowledged. Dr David A. Hrovat is thanked for the generation of the spin density plots of B and 3C. The experimental work in Reading was conducted with the support from Spectroelectrochemistry Reading, a spinout company of the University. Publisher Copyright: {\textcopyright} 2022 The Royal Society of Chemistry.",

year = "2022",

month = jul,

day = "7",

doi = "10.1039/d2dt00419d",

language = "English",

volume = "51",

pages = "9748--9769",

journal = "Dalton Transactions",

issn = "1477-9226",

publisher = "Royal Society of Chemistry",

number = "25",

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Orton, GRF, Ghosh, S, Alker, L, Sarker, JC, Pugh, D, Richmond, MG, Hartl, F & Hogarth, G 2022, 'Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe₄S₄ surrogates', Dalton Transactions, vol. 51, no. 25, pp. 9748-9769. https://doi.org/10.1039/d2dt00419d

Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe₄S₄ surrogates. / Orton, Georgia R.F.; Ghosh, Shishir; Alker, Lucy et al.
In: Dalton Transactions, Vol. 51, No. 25, 07.07.2022, p. 9748-9769.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands

T2 - synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe4S4 surrogates

AU - Orton, Georgia R.F.

AU - Ghosh, Shishir

AU - Alker, Lucy

AU - Sarker, Jagodish C.

AU - Pugh, David

AU - Richmond, Michael G.

AU - Hartl, František

AU - Hogarth, Graeme

N1 - Funding Information: We thank the Commonwealth Scholarship Commission for the award of Commonwealth Scholarships (SG and JCS) and King's College London (GRFO) for PhD funding. GH thanks The Royal Society of Chemistry for an International Authors Grant which allowed this work to be developed during his visit to the University of North Texas and King's College London for funding. We thank Dr Nathan Patmore (University of Huddersfield) for some early IR-SEC on 1, Professor Katherine J. Holt (UCL) for the initial electrochemical study on 1, Dr Nathan Hollingsworth (ex-UCL) for part supervision of LA, and Kishan Muthu (KCL) for early attempts to prepare 2 while working under the supervision of GRFO. MGR acknowledges financial support from the Robert A. Welch Foundation (Grant B-1093-MGR). Computational resources through the High-Performance Computing Services and CASCaM at the University of North Texas are acknowledged. Dr David A. Hrovat is thanked for the generation of the spin density plots of B and 3C. The experimental work in Reading was conducted with the support from Spectroelectrochemistry Reading, a spinout company of the University. Publisher Copyright: © 2022 The Royal Society of Chemistry.

PY - 2022/7/7

Y1 - 2022/7/7

N2 - [FeFe]-Ase biomimics containing a redox-active ferrocenyl diphosphine have been prepared and their ability to reduce protons and oxidise H2 studied, including 1,1′-bis(diphenylphosphino)ferrocene (dppf) complexes Fe2(CO)4(μ-dppf)(μ-S(CH2)nS) (n = 2, edt; n = 3, pdt) and Fe2(CO)4(μ-dppf)(μ-SAr)2 (Ar = Ph, p-tolyl, p-C6H4NH2), together with the more electron-rich 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf) complex Fe2(CO)4(μ-dcpf)(μ-pdt). Crystallographic characterisation of four of these show similar overall structures, the diphosphine spanning an elongated Fe-Fe bond (ca. 2.6 Å), lying trans to one sulfur and cis to the second. In solution the diphosphine is flexible, as shown by VT NMR studies, suggesting that Fe2⋯Fe distances of ca. 4.5-4.7 Å in the solid state vary in solution. Cyclic voltammetry, IR spectroelectrochemistry and DFT calculations have been used to develop a detailed picture of electronic and structural changes occurring upon oxidation. In MeCN, Fe2(CO)4(μ-dppf)(μ-pdt) shows two chemically reversible one-electron oxidations occurring sequentially at Fe2 and Fc sites respectively. For other dppf complexes, reversibility of the first oxidation is poor, consistent with an irreversible structural change upon removal of an electron from the Fe2 centre. In CH2Cl2, Fe2(CO)4(μ-dcpf)(μ-pdt) shows a quasi-reversible first oxidation together with subsequent oxidations suggesting that the generated cation has some stability but slowly rearranges. Both pdt complexes readily protonate upon addition of HBF4·Et2O to afford bridging-hydride cations, [Fe2(CO)4(μ-H)(μ-dcpf)(μ-pdt)]+, species which catalytically reduce protons to generate H2. In the presence of pyridine, [Fe2(CO)4(μ-dppf)(μ-pdt)]2+ catalytically oxidises H2 but none of the other complexes do this, probably resulting from the irreversible nature of their first oxidation. Mechanistic details of both proton reduction and H2 oxidation have been studied by DFT allowing speculative reaction schemes to be developed.

AB - [FeFe]-Ase biomimics containing a redox-active ferrocenyl diphosphine have been prepared and their ability to reduce protons and oxidise H2 studied, including 1,1′-bis(diphenylphosphino)ferrocene (dppf) complexes Fe2(CO)4(μ-dppf)(μ-S(CH2)nS) (n = 2, edt; n = 3, pdt) and Fe2(CO)4(μ-dppf)(μ-SAr)2 (Ar = Ph, p-tolyl, p-C6H4NH2), together with the more electron-rich 1,1′-bis(dicyclohexylphosphino)ferrocene (dcpf) complex Fe2(CO)4(μ-dcpf)(μ-pdt). Crystallographic characterisation of four of these show similar overall structures, the diphosphine spanning an elongated Fe-Fe bond (ca. 2.6 Å), lying trans to one sulfur and cis to the second. In solution the diphosphine is flexible, as shown by VT NMR studies, suggesting that Fe2⋯Fe distances of ca. 4.5-4.7 Å in the solid state vary in solution. Cyclic voltammetry, IR spectroelectrochemistry and DFT calculations have been used to develop a detailed picture of electronic and structural changes occurring upon oxidation. In MeCN, Fe2(CO)4(μ-dppf)(μ-pdt) shows two chemically reversible one-electron oxidations occurring sequentially at Fe2 and Fc sites respectively. For other dppf complexes, reversibility of the first oxidation is poor, consistent with an irreversible structural change upon removal of an electron from the Fe2 centre. In CH2Cl2, Fe2(CO)4(μ-dcpf)(μ-pdt) shows a quasi-reversible first oxidation together with subsequent oxidations suggesting that the generated cation has some stability but slowly rearranges. Both pdt complexes readily protonate upon addition of HBF4·Et2O to afford bridging-hydride cations, [Fe2(CO)4(μ-H)(μ-dcpf)(μ-pdt)]+, species which catalytically reduce protons to generate H2. In the presence of pyridine, [Fe2(CO)4(μ-dppf)(μ-pdt)]2+ catalytically oxidises H2 but none of the other complexes do this, probably resulting from the irreversible nature of their first oxidation. Mechanistic details of both proton reduction and H2 oxidation have been studied by DFT allowing speculative reaction schemes to be developed.

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