Quasiphosphonium Intermediates. Part 3. Preparation, Structure, and Reactivity of Alkoxyphosphonium Halides in the Reaction of Neopentyl Diphenylphosphinite, Dineopentyl Phenylphosphinite, and Trineopentyl Phosphite with Halogenomethanes and the Effect of Phenoxy-substituenst on the ...

Article abstract of DOI:10.1039/P29830001363

The reactions of neopenthyl diphenylphosphinite with chloro-, bromo-, or iodo-methane and of dineopentyl phenylphosphphonite with bromo- or iodo-methane yield crystalline alkoxyphosphonium halides.In deuteriochloroform these intermediates decompose by a first-order process which involves rate-determining collapse of the phosphonium halide ion-pair with S_N2-type fission of the alkyl-oxygen bond.Rates for chloride, bromide, and iodide are similar.In a more ionising medium (deuterioacetonitrile) dissociation leads to stabilisation of the intermediates and to deviation from first-order decomposition.Previously determined X-ray diffraction data for the bromides, together with relative rates of decomposition in deuteriochloroform for intermediates in the series Ph_n(RO)_3-nP⁺MeX^- (n = 0,1, or 2) suggest that the stability and reactivity of alkoxyphosphonium intermediates are determined largely by inductive rather than mesomeric effects of ligands.The presence of phenoxy-substituents on phosphorus may cause a tendency towards S_N1-type fission of the alkyl-oxygen bond in certain circumstances.