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Synthesis and molecular structures of the 52-electron triiron telluride clusters [Fe3(CO)8(μ3-Te)2(κ2-diphosphine)] - Electrochemical properties and activity as proton reduction catalysts

Rahaman, Ahibur LU ; Lisensky, George C. LU ; Tocher, Derek A. ; Richmond, Michael G. ; Hogarth, Graeme and Nordlander, Ebbe LU (2018) In Journal of Organometallic Chemistry 867. p.381-390
Abstract

Heating the 50-electron cluster [Fe3(CO)9 (μ3-Te)2] (1) with the diphosphines Ph2P-R-PPh2 [R = -CH2CH2- (dppe), Z-CH=CH- (dppv), 1,2-C6H4 (dppb), -CH2CH2CH2- (dpp), ferrocenyl (dppf), naphthalenyl (dppbn)] in benzene affords the 52-electron diphosphine-containing tellurium-capped triiron clusters [Fe3(CO)8 (μ3-Te)2 (κ2-diphosphine)] (diphosphine = dppe, dppv, dppb, dpp, dppf, dppnd) (2–7) in moderate yields, resulting from both phosphine addition and carbonyl loss. With 1,2-bis(diphenylphosphino)benzene (dppb) a second product is the cubane... (More)

Heating the 50-electron cluster [Fe3(CO)9 (μ3-Te)2] (1) with the diphosphines Ph2P-R-PPh2 [R = -CH2CH2- (dppe), Z-CH=CH- (dppv), 1,2-C6H4 (dppb), -CH2CH2CH2- (dpp), ferrocenyl (dppf), naphthalenyl (dppbn)] in benzene affords the 52-electron diphosphine-containing tellurium-capped triiron clusters [Fe3(CO)8 (μ3-Te)2 (κ2-diphosphine)] (diphosphine = dppe, dppv, dppb, dpp, dppf, dppnd) (2–7) in moderate yields, resulting from both phosphine addition and carbonyl loss. With 1,2-bis(diphenylphosphino)benzene (dppb) a second product is the cubane cluster [Fe4(CO)10(μ3-Te)4 (κ2-dppb)] (8). Cyclic voltammetry measurements on 2–7 reveal that all clusters show irreversible reductive behaviour at ca. −1.85 V with a series of associated small back oxidation waves, suggesting that reduction leads to significant structural change but that this can be reversed chemically. Oxidation occurs at relatively low potentials and is diphosphine-dependent. The first oxidation appears at ca. +0.35 V for 2–6 with a small degree of reversibility but is as low as +0.14 V for the bis(diphenylphosphino)naphthalene derivative 7 and in some cases is followed by further closely-spaced oxidation. Addition of [Cp2Fe][PF6] to 2–7 results in the formation of new clusters formulated as [Fe3(CO)8(μ3-Te)2(κ2-diphosphine)]+, with their IR spectra suggesting oxidation at the diiron centre. This is supported by computational studies (DFT) of the bis(diphenylphosphino)propane cluster 5 showing that the HOMO is the Fe–Fe σ-bonding orbital, while the LUMO is centered on the diphosphine-substituted iron atom and has significant Fe–Te σ∗-anti-bonding character consistent with the irreversible nature of the reduction. Complexes 2–7 have been examined as proton reduction catalysts in the presence of para-toluenesulfonic acid (TsOH). All are active at their first reduction potential, with a second catalytic process being observed at slightly higher potentials. While their overall electrocatalytic behaviour is similar to that noted for [Fe2(CO)6{μ-E(CH2)3E}] (E = S, Se, Te), the DFT results suggest that as the added electron is localised on the unique iron atom. The mechanistic aspects of hydrogen formation are likely to be quite different from the more widely studied diiron models.

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organization
publishing date
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Contribution to journal
publication status
published
subject
keywords
Diphosphine, Electrochemistry, Iron, Proton reduction, Tellurium
in
Journal of Organometallic Chemistry
volume
867
pages
10 pages
publisher
Elsevier
external identifiers
  • scopus:85046656171
ISSN
0022-328X
DOI
10.1016/j.jorganchem.2018.03.038
language
English
LU publication?
yes
id
ef11a693-42e7-46fa-a0d9-1dba3335a06e
date added to LUP
2018-05-25 14:27:13
date last changed
2022-03-17 07:42:05
@article{ef11a693-42e7-46fa-a0d9-1dba3335a06e,
  abstract     = {{<p>Heating the 50-electron cluster [Fe<sub>3</sub>(CO)<sub>9</sub> (μ<sub>3</sub>-Te)<sub>2</sub>] (1) with the diphosphines Ph<sub>2</sub>P-R-PPh<sub>2</sub> [R = -CH<sub>2</sub>CH<sub>2</sub>- (dppe), Z-CH=CH- (dppv), 1,2-C<sub>6</sub>H<sub>4</sub> (dppb), -CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>- (dpp), ferrocenyl (dppf), naphthalenyl (dppbn)] in benzene affords the 52-electron diphosphine-containing tellurium-capped triiron clusters [Fe<sub>3</sub>(CO)<sub>8</sub> (μ<sub>3</sub>-Te)<sub>2</sub> (κ<sup>2</sup>-diphosphine)] (diphosphine = dppe, dppv, dppb, dpp, dppf, dppnd) (2–7) in moderate yields, resulting from both phosphine addition and carbonyl loss. With 1,2-bis(diphenylphosphino)benzene (dppb) a second product is the cubane cluster [Fe<sub>4</sub>(CO)<sub>10</sub>(μ<sub>3</sub>-Te)<sub>4</sub> (κ<sup>2</sup>-dppb)] (8). Cyclic voltammetry measurements on 2–7 reveal that all clusters show irreversible reductive behaviour at ca. −1.85 V with a series of associated small back oxidation waves, suggesting that reduction leads to significant structural change but that this can be reversed chemically. Oxidation occurs at relatively low potentials and is diphosphine-dependent. The first oxidation appears at ca. +0.35 V for 2–6 with a small degree of reversibility but is as low as +0.14 V for the bis(diphenylphosphino)naphthalene derivative 7 and in some cases is followed by further closely-spaced oxidation. Addition of [Cp<sub>2</sub>Fe][PF<sub>6</sub>] to 2–7 results in the formation of new clusters formulated as [Fe<sub>3</sub>(CO)<sub>8</sub>(μ<sub>3</sub>-Te)<sub>2</sub>(κ<sup>2</sup>-diphosphine)]<sup>+</sup>, with their IR spectra suggesting oxidation at the diiron centre. This is supported by computational studies (DFT) of the bis(diphenylphosphino)propane cluster 5 showing that the HOMO is the Fe–Fe σ-bonding orbital, while the LUMO is centered on the diphosphine-substituted iron atom and has significant Fe–Te σ<sup>∗</sup>-anti-bonding character consistent with the irreversible nature of the reduction. Complexes 2–7 have been examined as proton reduction catalysts in the presence of para-toluenesulfonic acid (TsOH). All are active at their first reduction potential, with a second catalytic process being observed at slightly higher potentials. While their overall electrocatalytic behaviour is similar to that noted for [Fe<sub>2</sub>(CO)<sub>6</sub>{μ-E(CH<sub>2</sub>)<sub>3</sub>E}] (E = S, Se, Te), the DFT results suggest that as the added electron is localised on the unique iron atom. The mechanistic aspects of hydrogen formation are likely to be quite different from the more widely studied diiron models.</p>}},
  author       = {{Rahaman, Ahibur and Lisensky, George C. and Tocher, Derek A. and Richmond, Michael G. and Hogarth, Graeme and Nordlander, Ebbe}},
  issn         = {{0022-328X}},
  keywords     = {{Diphosphine; Electrochemistry; Iron; Proton reduction; Tellurium}},
  language     = {{eng}},
  month        = {{07}},
  pages        = {{381--390}},
  publisher    = {{Elsevier}},
  series       = {{Journal of Organometallic Chemistry}},
  title        = {{Synthesis and molecular structures of the 52-electron triiron telluride clusters [Fe<sub>3</sub>(CO)<sub>8</sub>(μ<sub>3</sub>-Te)<sub>2</sub>(κ<sup>2</sup>-diphosphine)] - Electrochemical properties and activity as proton reduction catalysts}},
  url          = {{http://dx.doi.org/10.1016/j.jorganchem.2018.03.038}},
  doi          = {{10.1016/j.jorganchem.2018.03.038}},
  volume       = {{867}},
  year         = {{2018}},
}