Electrochemistry Studies of [Ir(μ-pz)(COD)]2 in Halocarbon and Acetonitrile Solutions. Solvent Control of Sequential Electron-Transfer Thermodynamics

David C. Boyd, Gary S. Rodman, Kent R. Mann

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Abstract

Electrochemical studies of [Ir(μ-pz)(COD)]2(μ-pz = bridging pyrazolyl, COD = 1,5-cyclooctadiene) in halocarbon and CH3CN solutions have been completed. In CH2C12 solutions, the cyclic voltammogram (CV) of [Ir(μ-pz)(COD)]2 exhibits two, thermodynamically distinct one-electron oxidations. The first oxidation is quasi-reversible (= +0.424 in CH2C12/TBAH; TBAH = tetra-n-butylammonium hexafluorophosphate). is nearly independent of supporting anion (PF6 -, ClO4 -, and ASF6 -). The second oxidation is chemically irreversible. The position of EP,a for the second oxidation is variable due to complexation of [Ir(μ-pz)(COD)]2 2+ with the supporting anion. Ep,a occurs at +0.963, +1.280, and +1.383 V with ClO4 -, PF6 -, and AsF6 - as the supporting anion. Bulk electrolysis at potentials positive of the quasi-reversible oxidation results in the removal of 2.0 (1) electrons. A slow reaction on the CV time scale occurs between [Ir(μ-pz)(COD)]2 + and CH2Cl2 to form an IrIIIrII-containing product. The addition of CH3CN to CH2C12 solutions of [Ir(μ-pz)(COD)]2 causes the second electrode process to shift to less positive potentials. The first wave does not shift. At [CH3CN] ≈ 2.0 M, the second wave merges with the first to give a single feature that corresponds to a net two-electron process. The wave corresponding to this two-electron process also shifts toward negative potentials with increasing [CH3CN]. In neat CH3CN/TBAH solutions, the two-electron oxidation process occurs at +0.262 V. Bulk electrolysis in neat CH3CN solutions at potentials positive of the 2-electron process results in the removal of 2.0 (1) electrons. The observed shifts in electron-transfer thermodynamics arise from the strong complexation of two CH3CN ligands with the two-electron oxidized [Ir(μ-pz)(COD)]2 2+ complex. The potential for net two-electron-transfer chemistry from the lowest excited state of [Ir(μ-pz)(COD)]2 is discussed in terms of a modified Latimer diagram.

Original languageEnglish (US)
Pages (from-to)1779-1784
Number of pages6
JournalJournal of the American Chemical Society
Volume108
Issue number8
DOIs
StatePublished - Jan 1 1986

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