An electron spin resonance study of the electrochemical oxidation of phosphorus(III) compounds

Abstract

Radical cations generated during electrochemical oxidation of a series of trivalent phosphorus compounds, alone or in the presence of 3,3-dimethyl-2-t-butylbut-1-ene, have been studied using e.s.r. spectroscopy. The oxidations were carried out in nitrile or dichloromethane solvents and the cell containing the working electrode was situated in the cavity of the spectrometer. Oxidation of X₃P alone gives rise to the spectrum of the phosphine dimer cation radical, (X₃PPX₃)⁺, produced by rapid reaction of the initially formed phosphinium radical cation, X₃P⁺, with a further molecule of phosphine. Trialkyl phosphites did not give detectable concentrations of dimer cation radicals in nitrile solvents, probably because of preferential reaction of (RO)₃P⁺ with the solvent. In the presence of 3,3-dimethyl-2-t-butylbut-1-ene the spectra of the dimer cation radicals were completely or partially quenched and replaced by those of the adducts Bu^t₂ĊCH₂PX₃. The phosphorus hyperfine splittings of both (X₃PPX₃)⁺ and Bu^t₂ĊCH₂PX₃ increased with the electronegativity of the ligands X, and these trends are interpreted in terms of changes in hybridisation at phosphorus.