An electron spin resonance study of phosphoranyl radicals derived from tetra-alkyl esters of phosphorous phosphoric anhydride (RO)2POP(O)(OR)2

Abstract

A series of phosphoranyl radicals with the general structure (RO)₂P(X)OṖ(OR)₃(X = O or S) have been studied in solution using e.s.r. spectroscopy. The phosphoranyl radicals were produced by addition of photochemically generated t-butoxyl radicals to (RO)₂P(X)OP(OR)₂(X = O or S) or diethoxyphosphoryloxyl radicals (EtO)₂P(O)O to (RO)₃P (X = O). The e.s.r. spectra of these phosphoranyl radicals are consistent with a trigonal bipyramidal structure, and the apicophilicity of (RO)₂P(O)O is greater than that of RO. The spectrum of the cyclic radical [graphic omitted](O)(OEt)2 shows that apical and equatorial endocyclic alkoxy-substituents undergo rapid exchange. The fβ-scission of (EtO)₂Bu^tOPOP(O)(OEt)₂at –60° to give t-butyl radicals is 40 times slower than that of (EtO)₃ṖOBu^t.