- Chemical and Electrochemical Oxidation of CpRe(PAr3)2H2 Complexes To Give Stable 17-Electron Radical Cations. Disproportionation to Diamagnetic Species via Electron Transfer Catalysis
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Oxidations of CpRe(PAr3)2H2 complexes give stable .+ complexes in both acetonitrile and dichloromethane as determined by controlled-potential thin-layer coulometry and double-potential step chronocoulometry.The magnitude of Eo for the Re(III)/Re(IV) couple as detrmined by cyclic voltammetry is influenced by the aryl substituents in the CpRe2 complexes (1: X=H; 3: X=Me; 4: X=F; 5: X=MeO) with Eo becoming more positive as the ?-donating ability of the substituent decreases.Oxidation at more positive potentials presumably produces 2+, a diamagnetic 16-electron species, which reacts with the 17 electron species.This reaction is autocatalytic with the electron-transfer catalysis (ETC), giving current efficiencies of between 5 and 20 for each electron removed beyond the 17-electron species.In acetonitrile, the reaction driven by ETC gave equal amounts of two products, + and +, while in dichloromethane only the latter product was produced.Ferricinium hexafluorophospate oxidation in 1 gave +- (7) in 43percent yield and +- in 45percent yield.The structure of 7 was determined unambiguously by single-crystal X-ray crystallographic analysis.The molecule +- crystallizes in a trans geometry in monoclinic space group P22/c with Z=4, a=9.908(2) Angstroem, b=21.546(9) Angstroem, c=18.967(6) Angstroem, and β=99.12(2) deg.The + complexes exhibit reversible one-electron oxidations by cyclic voltammetry and show that the magnitude of Eo is once more a function of the electron-donating ability of the aryl substituents.The mechanism of chain propagation in the reactions of the .+ complexes involves either proton transfer or hydrogen atom transfer with the 16-ectron 2+ moieties to give species capable of oxidizing more of the 17-electron complex.
- Detty, Michael R.,Jones, William D.
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p. 5666 - 5673
(2007/10/02)
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