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Electrocatalytic proton-reduction behaviour of telluride-capped triiron clusters : tuning of overpotentials and stabilization of redox states relative to lighter chalcogenide analogues

Rahaman, Ahibur LU ; Lisensky, George C. LU ; Browder-Long, Jess ; Hrovat, David A. ; Richmond, Michael G. ; Nordlander, Ebbe LU and Hogarth, Graeme (2020) In Dalton Transactions 49(21). p.7133-7143
Abstract

Reaction of [Fe3(CO)93-Te)2] (1) with the corresponding phosphine has been used to prepare the phosphine-substituted tellurium-capped triiron clusters [Fe3(CO)93-Te)2(PPh3)] (2), [Fe3(CO)83-Te)2(PPh3)] (3) and [Fe3(CO)73-Te)2(µ-R2PXPR2)] (X = CH2, R = Ph (4), Cy (5); X = NPri, R = Ph (6)). The directly related cluster [Fe3(CO)73-CO)(µ3-Te)(µ-dppm)] (7) was isolated from the reaction of... (More)

Reaction of [Fe3(CO)93-Te)2] (1) with the corresponding phosphine has been used to prepare the phosphine-substituted tellurium-capped triiron clusters [Fe3(CO)93-Te)2(PPh3)] (2), [Fe3(CO)83-Te)2(PPh3)] (3) and [Fe3(CO)73-Te)2(µ-R2PXPR2)] (X = CH2, R = Ph (4), Cy (5); X = NPri, R = Ph (6)). The directly related cluster [Fe3(CO)73-CO)(µ3-Te)(µ-dppm)] (7) was isolated from the reaction of [Fe3(CO)10(µ-Ph2PCH2PPh2)] with elemental tellurium. The electrochemistry of these new clusters has been probed by cyclic voltammetry, and selected complexes have been tested as proton reduction catalysts. Each 50-electron dicapped cluster exhibits two reductive processes; the first has good chemical reversibility in all cases but the reversibility of the second is dependent upon the nature of the supporting ligands. For the parent cluster1and the diphosphine derivatives4-5this second reduction is reversible, but for the PPh3complex3it is irreversible, possibly as a result of CO or phosphine loss. The nature of the reduced products of1has been probed by DFT calculations. Upon addition of one electron, an elongation of one of the Fe-Te bonding interactions is found, while the addition of the second electron affords an open-shell triplet which is more stable by 8.8 kcal mol-1than the closed-shell singlet dianion and has two elongated Fe-Te bonds. The phosphine-substituted clusters also exhibit oxidation chemistry but with poor reversibility in all cases. Since the reduction potentials for the tellurium-capped clusters occur at more positive potentials than for the sulfur and selenium analogues, and the redox processes also show better reversibility than for the S/Se analogues, the tellurium-capped clusters1and3-5have been examined as proton reduction catalysts. In the presence ofp-toluenesulfonic acid (TsOH) or trifluoroacetic acid (TFA), these clusters reduce protons to H2at both their first and second reduction potentials. Electron uptake at the second reduction potential is far greater than the first, suggesting that the open-shell triplet dianions are efficient catalysts. As expected, the catalytic overpotential increases upon successive phosphine substitution but so does the current response. A mechanistic scheme that takes the roles of the supporting ligands on the preferred route(s) to H2production and release into account is presented.

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Contribution to journal
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Dalton Transactions
volume
49
issue
21
pages
11 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85085645004
  • pmid:32406893
ISSN
1477-9226
DOI
10.1039/d0dt00556h
language
English
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yes
id
85b60be1-b548-4114-a7d8-59af1c4cace0
date added to LUP
2020-06-12 13:31:14
date last changed
2021-04-20 05:13:22
@article{85b60be1-b548-4114-a7d8-59af1c4cace0,
  abstract     = {<p>Reaction of [Fe<sub>3</sub>(CO)<sub>9</sub>(µ<sub>3</sub>-Te)<sub>2</sub>] (1) with the corresponding phosphine has been used to prepare the phosphine-substituted tellurium-capped triiron clusters [Fe<sub>3</sub>(CO)<sub>9</sub>(µ<sub>3</sub>-Te)<sub>2</sub>(PPh<sub>3</sub>)] (2), [Fe<sub>3</sub>(CO)<sub>8</sub>(µ<sub>3</sub>-Te)<sub>2</sub>(PPh<sub>3</sub>)] (3) and [Fe<sub>3</sub>(CO)<sub>7</sub>(µ<sub>3</sub>-Te)<sub>2</sub>(µ-R<sub>2</sub>PXPR<sub>2</sub>)] (X = CH<sub>2</sub>, R = Ph (4), Cy (5); X = NPr<sup>i</sup>, R = Ph (6)). The directly related cluster [Fe<sub>3</sub>(CO)<sub>7</sub>(µ<sub>3</sub>-CO)(µ<sub>3</sub>-Te)(µ-dppm)] (7) was isolated from the reaction of [Fe<sub>3</sub>(CO)<sub>10</sub>(µ-Ph<sub>2</sub>PCH<sub>2</sub>PPh<sub>2</sub>)] with elemental tellurium. The electrochemistry of these new clusters has been probed by cyclic voltammetry, and selected complexes have been tested as proton reduction catalysts. Each 50-electron dicapped cluster exhibits two reductive processes; the first has good chemical reversibility in all cases but the reversibility of the second is dependent upon the nature of the supporting ligands. For the parent cluster1and the diphosphine derivatives4-5this second reduction is reversible, but for the PPh<sub>3</sub>complex3it is irreversible, possibly as a result of CO or phosphine loss. The nature of the reduced products of1has been probed by DFT calculations. Upon addition of one electron, an elongation of one of the Fe-Te bonding interactions is found, while the addition of the second electron affords an open-shell triplet which is more stable by 8.8 kcal mol<sup>-1</sup>than the closed-shell singlet dianion and has two elongated Fe-Te bonds. The phosphine-substituted clusters also exhibit oxidation chemistry but with poor reversibility in all cases. Since the reduction potentials for the tellurium-capped clusters occur at more positive potentials than for the sulfur and selenium analogues, and the redox processes also show better reversibility than for the S/Se analogues, the tellurium-capped clusters1and3-5have been examined as proton reduction catalysts. In the presence ofp-toluenesulfonic acid (TsOH) or trifluoroacetic acid (TFA), these clusters reduce protons to H<sub>2</sub>at both their first and second reduction potentials. Electron uptake at the second reduction potential is far greater than the first, suggesting that the open-shell triplet dianions are efficient catalysts. As expected, the catalytic overpotential increases upon successive phosphine substitution but so does the current response. A mechanistic scheme that takes the roles of the supporting ligands on the preferred route(s) to H<sub>2</sub>production and release into account is presented.</p>},
  author       = {Rahaman, Ahibur and Lisensky, George C. and Browder-Long, Jess and Hrovat, David A. and Richmond, Michael G. and Nordlander, Ebbe and Hogarth, Graeme},
  issn         = {1477-9226},
  language     = {eng},
  number       = {21},
  pages        = {7133--7143},
  publisher    = {Royal Society of Chemistry},
  series       = {Dalton Transactions},
  title        = {Electrocatalytic proton-reduction behaviour of telluride-capped triiron clusters : tuning of overpotentials and stabilization of redox states relative to lighter chalcogenide analogues},
  url          = {http://dx.doi.org/10.1039/d0dt00556h},
  doi          = {10.1039/d0dt00556h},
  volume       = {49},
  year         = {2020},
}