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 - 2022/6/6
Y1 - 2022/6/6
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.
UR - http://www.scopus.com/inward/record.url?scp=85132335373&partnerID=8YFLogxK
U2 - 10.1039/d2dt00419d
DO - 10.1039/d2dt00419d
M3 - Article
C2 - 35703728
AN - SCOPUS:85132335373
SN - 1477-9226
VL - 51
SP - 9748
EP - 9769
JO - Dalton Transactions
JF - Dalton Transactions
IS - 25
ER -