Experimental and digital simulation 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

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Abstract

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)]+PF 6- were studied by cyclic voltammetry in MeCN (0.2 M nBu4N+PF6-). The tungsten anion [CpW(CO)2(IMes)]- showed a fully reversible one-electron oxidation with E1/2 = -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 -0.49 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 K eq = 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).

Original languageEnglish
Pages (from-to)4555-4563
Number of pages9
JournalOrganometallics
Volume30
Issue number17
DOIs
Publication statusPublished - Sep 12 2011

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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