Chemical and Electrochemical Oxidation of CpRe(PAr3)2H2 Complexes To Give Stable 17-Electron Radical Cations. Disproportionation to Diamagnetic Species via Electron Transfer Catalysis

Article abstract of DOI:10.1021/ja00253a017

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 E^o 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 E^o 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 E^o 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.