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Smith, Paul F. & Hunt, Liam & Laursen, Anders B. & Sagar, Viral & Kaushik, Shivam & Calvinho, Karin U. D. & Marotta, Gabriele & Mosconi, Edoardo & De Angelis, Filippo & Dismukes, G. Charles (2015). Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH– Addition. Journal of the American Chemical Society, 137(49), 15460-15468. Retrieved from https://doi.org/doi:10.7282/T37P91BG

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Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH– Addition (2015)
Paul F. Smith, Liam Hunt, Anders B. Laursen, Viral Sagar, Shivam Kaushik, Karin U. D. Calvinho, Gabriele Marotta, Edoardo Mosconi, Filippo De Angelis, G. Charles Dismukes
Journal of the American Chemical Society 137(49): 15460-15468.
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AbstractThe cobalt cubium Co4O4(OAc)4(py)4(ClO4) (1A+) containing the mixed valence [Co4O4]5+ core is shown by multiple spectroscopic methods to react with hydroxide (OH-) but not with water molecules to produce O2. The yield of reaction products is stoichiometric (>99.5%): 4 1A+ + 4 OH- → O2 + 2 H2O + 4 1A. By contrast, the structurally homologous cubium Co4O4(trans-OAc)2(bpy)4(ClO4)3, 1B(ClO4)3 produces no O2. EPR/NMR spectroscopies show clean conversion to cubane 1A during O2 evolution with no Co2+ or Co3O4 side products. Mass spectrometry of the reaction between isotopically labeled µ-16O(bridging-oxo) 1A+ and 18O-bicarbonate/water shows: 1) no exchange of 18O into the bridging oxos of 1A+, and 2) 36O2 is the major product, thus requiring two OH- in the reactive intermediate. DFT calculations of solvated intermediates suggest that addition of two OH- to 1A+ via OH- insertion into Co-OAc bonds is energetically favored, followed by outer-sphere oxidation to intermediate [1A(OH)2]0. The absence of O2 production by cubium 1B3+ indicates the reactive intermediate derived from 1A+ requires gem-1,1-dihydoxo stereochemistry to perform O-O bond formation. Outer-sphere oxidation of this intermediate by 2 eq. 1A+ accounts for the final stoichiometry. Collectively, these results, and recent literature (Faraday Disc., doi:10.1039/C5FD00076A and J.Am.Chem.Soc 2015, 12865-12872) validate the [Co4O4]4+/5+ cubane core as an intrinsic catalyst for oxidation of hydroxide by an inner-sphere mechanism.
Persistent URLhttps://doi.org/doi:10.7282/T37P91BG
SubjectsOxidation, Cobalt cubium
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