Homolytic organometallic reactions. Part XII. An electron spin resonance study of the α-scission of alkoxyalkylphosphoranyl radicals in solution

Abstract

The structures and the kinetics of α-scission of a series of alkoxyalkylphosphoranyl radicals have been studied by e.s.r. spectroscopy in solution. These radicals were generated by the addition of photolytically produced alkoxyl radicals to alkoxyalkylphosphines. The stability towards α-scission of the radicals Et_nṖ(OR)_{4 –n} exhibits a maximum for n= 2. Phosphoranyl radicals R₂Ṗ(OBu^t)₂ fragment by loss of an alkyl radical, R·, with increasing rate along the series R = Me < Bu^t < Et ∼ Prⁿ < Prⁱ∼ Bu^s < allyl. These results are interpreted in terms of a preference for departure of an alkyl radical from an apical rather than an equatorial site, in α-scission of the trigonal bipyramidal phosphoranyl radical. Factors which influence the relative rates of α- and β-scission of alkoxyalkylphosphoranyl radicals are discussed.