Trimethylsilyl esters of phosphorus acids. III. Esters of difluoro- and bis(trifluoromethyl)phosphinous and -thiophosphinous acids

Article abstract of DOI:10.1021/ic50124a032

The esters R₂PESi(CH₃)₃ (R = F, E = O; R = CF₃, E = O, S) have been prepared using one or more of four synthetic routes (CF₃)₂PSSi(CH₃)₃ is the first known example of a P^III-S-Si bridged compound, but the analogous difluoro ester F₂PSSi(CH₃)₃ appears to be thermally unstable at 25°. Attempted syntheses of the P(V) isomers R₂P(E)Si(CH₃)₃ gave only the P(III) forms, indicating that these systems are susceptible to anti-Arbuzov rearrangements. The difference in the stability and polarity between the P-O-Si and P-S-Si bridge units was demonstrated by the reactions of the esters with HCl and (CH₃)₂NH. At least three different reactions of the esters with dimethylamine were observed: cleavage at the E-Si bond with or without concomitant subsequent reaction of (CH₃)₃SiN(CH₃)₂ with the ionic product R₂PE^- and, in the case of (CF₃)₂POSi(CH₃)₃, displacement of CF₃H to yield CF₃[N(CH₃)₂]POSi(CH₃)₃. The latter phosphine showed a temperature-dependent nmr spectrum consistent with conformational isomerism of the N(CH₃)₂ group.