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Hydrogenase biomimetics with redox-active ligands : Electrocatalytic proton reduction by [Fe2(CO)42-diamine)(μ-edt)] (diamine = 2,2′-bipy, 1,10-phen)

Ghosh, Shishir; Rahaman, Ahibur LU ; Holt, Katherine B; Nordlander, Ebbe LU ; Richmond, Michael G.; Kabir, Shariff E and Hogarth, Graeme (2016) In Polyhedron 116. p.127-135
Abstract

Diiron complexes bearing redox active diamine ligands have been studied as models of the active site of [FeFe]-hydrogenases. Heating [Fe2(CO)6(μ-edt)] (edt = 1,2-ethanedithiolate) with 2,2′-bipyridine (2,2′-bipy) or 1,10-phenanthroline (1,10-phen) in MeCN in the presence of Me3NO leads to the formation of [Fe2(CO)42-2,2′-bipy)(μ-edt)] (1-edt) and [Fe2(CO)42-1,10-phen)(μ-edt)] (2-edt), respectively, in moderate yields. In the solid state the diamine resides in dibasal sites, while both dibasal and apical–basal isomers are present in solution. Both stereoisomers protonate readily upon addition of strong acids. Cyclic voltammetry in MeCN... (More)

Diiron complexes bearing redox active diamine ligands have been studied as models of the active site of [FeFe]-hydrogenases. Heating [Fe2(CO)6(μ-edt)] (edt = 1,2-ethanedithiolate) with 2,2′-bipyridine (2,2′-bipy) or 1,10-phenanthroline (1,10-phen) in MeCN in the presence of Me3NO leads to the formation of [Fe2(CO)42-2,2′-bipy)(μ-edt)] (1-edt) and [Fe2(CO)42-1,10-phen)(μ-edt)] (2-edt), respectively, in moderate yields. In the solid state the diamine resides in dibasal sites, while both dibasal and apical–basal isomers are present in solution. Both stereoisomers protonate readily upon addition of strong acids. Cyclic voltammetry in MeCN shows that both complexes undergo irreversible oxidation and reduction, proposed to be a one- and two-electron process, respectively. The structures of neutral 2-edt and its corresponding one- and two-electron reduced species have been investigated by DFT calculations. In 2-edtthe added electron occupies a predominantly ligand-based orbital, and the iron–iron bond is maintained, being only slightly elongated. Addition of the second electron affords an open-shell triplet dianion where the second electron populates an Fe–Fe σ*antibonding orbital, resulting in effective scission of the iron–iron bond. The triplet state lies 4.2 kcal mol−1lower in energy than the closed-shell singlet dianion whose HOMO correlates nicely with the LUMO of the neutral species 2-edt. Electrocatalytic proton reduction by both complexes has been studied in MeCN using CF3CO2H as the proton source. These catalysis studies reveal that while at high acid concentrations the active catalytic species is [Fe2(CO)4(μ-H)(κ2-diamine)(μ-edt)]+, at low acid concentrations the two complexes follow different catalytic mechanisms being associated with differences in their relative rates of protonation.

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type
Contribution to journal
publication status
published
subject
keywords
Biomimic, Diamine, Electrochemistry, Hydrogenase, Redox active ligand
in
Polyhedron
volume
116
pages
9 pages
publisher
Elsevier
external identifiers
  • scopus:84971657219
  • wos:000382795100018
ISSN
0277-5387
DOI
10.1016/j.poly.2016.05.015
language
English
LU publication?
yes
id
6e3c9106-5acb-435c-b5e9-ab920277b916
date added to LUP
2017-02-08 10:33:54
date last changed
2017-11-05 05:13:20
@article{6e3c9106-5acb-435c-b5e9-ab920277b916,
  abstract     = {<p>Diiron complexes bearing redox active diamine ligands have been studied as models of the active site of [FeFe]-hydrogenases. Heating [Fe<sub>2</sub>(CO)<sub>6</sub>(μ-edt)] (edt = 1,2-ethanedithiolate) with 2,2′-bipyridine (2,2′-bipy) or 1,10-phenanthroline (1,10-phen) in MeCN in the presence of Me<sub>3</sub>NO leads to the formation of [Fe<sub>2</sub>(CO)<sub>4</sub>(κ<sup>2</sup>-2,2′-bipy)(μ-edt)] (1-edt) and [Fe<sub>2</sub>(CO)<sub>4</sub>(κ<sup>2</sup>-1,10-phen)(μ-edt)] (2-edt), respectively, in moderate yields. In the solid state the diamine resides in dibasal sites, while both dibasal and apical–basal isomers are present in solution. Both stereoisomers protonate readily upon addition of strong acids. Cyclic voltammetry in MeCN shows that both complexes undergo irreversible oxidation and reduction, proposed to be a one- and two-electron process, respectively. The structures of neutral 2-edt and its corresponding one- and two-electron reduced species have been investigated by DFT calculations. In 2-edt<sup>−</sup>the added electron occupies a predominantly ligand-based orbital, and the iron–iron bond is maintained, being only slightly elongated. Addition of the second electron affords an open-shell triplet dianion where the second electron populates an Fe–Fe σ<sup>*</sup>antibonding orbital, resulting in effective scission of the iron–iron bond. The triplet state lies 4.2 kcal mol<sup>−1</sup>lower in energy than the closed-shell singlet dianion whose HOMO correlates nicely with the LUMO of the neutral species 2-edt. Electrocatalytic proton reduction by both complexes has been studied in MeCN using CF<sub>3</sub>CO<sub>2</sub>H as the proton source. These catalysis studies reveal that while at high acid concentrations the active catalytic species is [Fe<sub>2</sub>(CO)<sub>4</sub>(μ-H)(κ<sup>2</sup>-diamine)(μ-edt)]<sup>+</sup>, at low acid concentrations the two complexes follow different catalytic mechanisms being associated with differences in their relative rates of protonation.</p>},
  author       = {Ghosh, Shishir and Rahaman, Ahibur and Holt, Katherine B and Nordlander, Ebbe and Richmond, Michael G. and Kabir, Shariff E and Hogarth, Graeme},
  issn         = {0277-5387},
  keyword      = {Biomimic,Diamine,Electrochemistry,Hydrogenase,Redox active ligand},
  language     = {eng},
  pages        = {127--135},
  publisher    = {Elsevier},
  series       = {Polyhedron},
  title        = {Hydrogenase biomimetics with redox-active ligands : Electrocatalytic proton reduction by [Fe<sub>2</sub>(CO)<sub>4</sub>(κ<sup>2</sup>-diamine)(μ-edt)] (diamine = 2,2′-bipy, 1,10-phen)},
  url          = {http://dx.doi.org/10.1016/j.poly.2016.05.015},
  volume       = {116},
  year         = {2016},
}