Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment: Characterization of Remarkably Stable Ir(IV,V) Complexes

Shashi Bhushan Sinha, Dimitar Y. Shopov, Liam S. Sharninghausen, Christopher J. Stein, Brandon Q. Mercado, David Balcells, Thomas Bondo Pedersen, Markus Reiher, Gary W Brudvig, Robert H. Crabtree

Research output: Contribution to journalArticle

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Abstract

Chemical and electrochemical oxidation or reduction of our recently reported Ir(IV,IV) mono-μ-oxo dimers results in the formation of fully characterized Ir(IV,V) and Ir(III,III) complexes. The Ir(IV,V) dimers are unprecedented and exhibit remarkable stability under ambient conditions. This stability and modest reduction potential of 0.99 V vs NHE is in part attributed to complete charge delocalization across both Ir centers. Trends in crystallographic bond lengths and angles shed light on the structural changes accompanying oxidation and reduction. The similarity of these mono-μ-oxo dimers to our Ir "blue solution" water-oxidation catalyst gives insight into potential reactive intermediates of this structurally elusive catalyst. Additionally, a highly reactive material, proposed to be a Ir(V,V) μ-oxo species, is formed on electrochemical oxidation of the Ir(IV,V) complex in organic solvents at 1.9 V vs NHE. Spectroelectrochemistry shows reversible conversion between the Ir(IV,V) and proposed Ir(V,V) species without any degradation, highlighting the exceptional oxidation resistance of the 2-(2-pyridinyl)-2-propanolate (pyalk) ligand and robustness of these dimers. The Ir(III,III), Ir(IV,IV) and Ir(IV,V) redox states have been computationally studied both with DFT and multiconfigurational calculations. The calculations support the stability of these complexes and provide further insight into their electronic structures.

Original languageEnglish
Pages (from-to)9672-9683
Number of pages12
JournalJournal of the American Chemical Society
Volume139
Issue number28
DOIs
Publication statusPublished - Jul 19 2017

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Iridium
Dimers
Oxidation-Reduction
Electrochemical oxidation
Spectroelectrochemistry
Ligands
Oxidation
Catalysts
Oxidation resistance
Bond length
Discrete Fourier transforms
Organic solvents
Electronic structure
Degradation
Water
aniline blue

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Sinha, S. B., Shopov, D. Y., Sharninghausen, L. S., Stein, C. J., Mercado, B. Q., Balcells, D., ... Crabtree, R. H. (2017). Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment: Characterization of Remarkably Stable Ir(IV,V) Complexes. Journal of the American Chemical Society, 139(28), 9672-9683. https://doi.org/10.1021/jacs.7b04874

Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment : Characterization of Remarkably Stable Ir(IV,V) Complexes. / Sinha, Shashi Bhushan; Shopov, Dimitar Y.; Sharninghausen, Liam S.; Stein, Christopher J.; Mercado, Brandon Q.; Balcells, David; Pedersen, Thomas Bondo; Reiher, Markus; Brudvig, Gary W; Crabtree, Robert H.

In: Journal of the American Chemical Society, Vol. 139, No. 28, 19.07.2017, p. 9672-9683.

Research output: Contribution to journalArticle

Sinha, SB, Shopov, DY, Sharninghausen, LS, Stein, CJ, Mercado, BQ, Balcells, D, Pedersen, TB, Reiher, M, Brudvig, GW & Crabtree, RH 2017, 'Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment: Characterization of Remarkably Stable Ir(IV,V) Complexes', Journal of the American Chemical Society, vol. 139, no. 28, pp. 9672-9683. https://doi.org/10.1021/jacs.7b04874
Sinha, Shashi Bhushan ; Shopov, Dimitar Y. ; Sharninghausen, Liam S. ; Stein, Christopher J. ; Mercado, Brandon Q. ; Balcells, David ; Pedersen, Thomas Bondo ; Reiher, Markus ; Brudvig, Gary W ; Crabtree, Robert H. / Redox Activity of Oxo-Bridged Iridium Dimers in an N,O-Donor Environment : Characterization of Remarkably Stable Ir(IV,V) Complexes. In: Journal of the American Chemical Society. 2017 ; Vol. 139, No. 28. pp. 9672-9683.
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abstract = "Chemical and electrochemical oxidation or reduction of our recently reported Ir(IV,IV) mono-μ-oxo dimers results in the formation of fully characterized Ir(IV,V) and Ir(III,III) complexes. The Ir(IV,V) dimers are unprecedented and exhibit remarkable stability under ambient conditions. This stability and modest reduction potential of 0.99 V vs NHE is in part attributed to complete charge delocalization across both Ir centers. Trends in crystallographic bond lengths and angles shed light on the structural changes accompanying oxidation and reduction. The similarity of these mono-μ-oxo dimers to our Ir {"}blue solution{"} water-oxidation catalyst gives insight into potential reactive intermediates of this structurally elusive catalyst. Additionally, a highly reactive material, proposed to be a Ir(V,V) μ-oxo species, is formed on electrochemical oxidation of the Ir(IV,V) complex in organic solvents at 1.9 V vs NHE. Spectroelectrochemistry shows reversible conversion between the Ir(IV,V) and proposed Ir(V,V) species without any degradation, highlighting the exceptional oxidation resistance of the 2-(2-pyridinyl)-2-propanolate (pyalk) ligand and robustness of these dimers. The Ir(III,III), Ir(IV,IV) and Ir(IV,V) redox states have been computationally studied both with DFT and multiconfigurational calculations. The calculations support the stability of these complexes and provide further insight into their electronic structures.",
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