Experimental and Digital Modeling Studies of the Electrochemical Oxidation of the Metal Anion [CpW(CO)2(IMes)]- and the 17-Electron Metal Radical CpW(CO)2(IMes)•. Kinetics and Thermodynamics of Capture and Release of MeCN by a Metal Radical and a Metal Cation
Journal Article
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· Organometallics, 30(17):4555-4563
The electrochemistry of [CpW(CO)2(IMes)] [K(18 crown 6)]+ (Cp = η5-C5H5, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), CpW(CO)2(IMes)•, and [CpW(CO)2(IMes)(MeCN)]+PF6 were studied by cyclic voltammetry in MeCN (0.2 M nBu4N+BF4 ). The tungsten anion [CpW(CO)2(IMes)]- showed a fully reversible one-electron oxidation with E½ = 1.65 V vs. Cp2Fe+/0. Oxidation of the resultant 17-electron radical CpW(CO)2(IMes)• was irreversible at all scan rates, affording the 18-electron solvent adduct [CpW(CO)2(IMes)(MeCN)]+. Reduction of [CpW(CO)2(IMes)(MeCN)]+ proceeded with loss of coordinated MeCN, and was followed by a second reduction to generate [CpW(CO)2(IMes)]-. Simultaneous digital simulation of voltammograms of [CpW(CO)2(IMes)]- and CpW(CO)2(IMes)• over a range of scan rates and concentrations gave estimates for E° of 0.491(2) V for the [CpW(CO)2(IMes)]+/• couple and 1.92 V for the [CpW(CO)2(IMes)(MeCN)]+/• couple. The neutral 19-electron radical complex CpW(CO)2(IMes)(MeCN)• is a stronger reducing agent (by 1.42 V) than the unsolvated 17-electron radical CpW(CO)2(IMes)•. Binding of MeCN by the unsolvated 16-electron cation [CpW(CO)2(IMes)]+ is exergonic with Keq = 1.2 × 1011 M 1 for [CpW(CO)2(IMes)]+ + MeCN [CpW(CO)2(IMes)(MeCN)]+. Expulsion of the MeCN ligand from the 19-electron complex CpW(CO)2(IMes)(MeCN)• is also exergonic, with Keq = 1.2 × 1013 M for CpW(CO)2(IMes)(MeCN)• CpW(CO)2(IMes)• + MeCN. Experimental and simulated cyclic voltammograms also account for the chemical reduction of the metal cation [CpW(CO)2(IMes)(MeCN)]+ by the metal anion [CpW(CO)2(IMes)]-, which ultimately produces two equivalents of the metal-centered radical CpW(CO)2(IMes)• This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1025080
- Report Number(s):
- PNNL-SA-78755; KC0302010
- Journal Information:
- Organometallics, 30(17):4555-4563, Journal Name: Organometallics, 30(17):4555-4563 Journal Issue: 17 Vol. 30; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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