Topics in Phosphorus-Fluorine Chemistry

The reactions between primary amines and phosphorus penta- fluoride were complex and yielded alkylammonium hexafiuorophosphates, RNH+3 PF6- (R = Me, Et, But), and bis(alkylamino)trifluorophos- phoranes, (RNH)2PF3 (R = Me, Et, But). In addition a 2:1 adduct, 2MeNH2. PF5, was formed in the reaction with methylamine whereas 1:1 adducts, RNH2. PF5 (R = Et, But), were produced with ethyl-amine and t-butylamine. The preparation of alkylaminotetrafluoro-phosphoranes, RNHPF4 (R = Et, But), by the thermal decomposition of the 1:1 adducts was studied. Methylaminotetrafluorophosphorane could be prepared by the reaction between raethylaminotrimethyl-silane, Me3SiNHMe, and phosphorus pentafluoride. The formation of diazafluorodiphosphetidines from alkylamino-fluorophosphoranes was studied. Phosphorus pentafluoride and phenyltetrafluorophosphorane reacted with (MeNH)2PF3 to give (F3PNMe)2 and PhF(F2PNMe)2 respectively, but the yield of these products was low. The reaction between primary amines and phosphorus trifluoride proceeded by a two step process. Alkylaminodifluorophosphines, RNHPF2 (R = Me, Et, But, Bun), were formed in the initial step. The nature of the subsequent step is believed to depend on the steric properties of the attacking amine. Bis(alkylamino)difluoro-phosphoranes, (RNH)2PF2H (R = Me, Et, Bun), were usually isolated, but the bulky t-butylamine produced bis(t-butylamino)fluoro-phosphine, (But NH)2PF The compounds isolated above were characterised by their n.m.r., i.r. and mass spectra. Several fragmentation modes for molecules of the type RNHP(F) are discussed. Infra-red correlations for the RNH-P group are also made. The bulk of the evidence suggests that the extra molecule of amine in 2MeNH2. PF5 is co-ordinated to the 1:1 adduct by means of N---H hydrogen-bonding. Several routes to produce PNP bridges were investigated. Difluorophosphino(tetrafluorophosphoranyl)methylamine, PF2NMePF4, was best prepared from the reaction between phosphorus penta- fluoride and difluorophosphino(trimethylsilyl)methylamine, Me3SiNMePF2, which was itself prepared from the reaction between heptamethyldisilazane and chlorodifluorophosphine. A similar reaction between POF3 and Me3SiNMePF2 only gave low yields of difluorophosphino(difluorophosphoryl)methylamine, PF2NMePOF2. The latter was more conveniently synthesized from chlorodifluoro phosphine and methylaminophosphoryl difluoride, MeNHPOF2. The ease of reaction between Me3SiNMeX (X = P(F), SiMe3) and a phosphorus-fluoride could be correlated with the Lewis basicity of the former and the Lewis acidity of the latter. The spectroscopic properties of the bridged compounds produced were examined. Attempts to prepare PNS bridges by the above routes failed, and possible reasons for this are discussed. The products isolated from the reaction of SOF2 with either MeNHPF2 or Me3SiNMePF2 included methylaminothiophosphoryl difluoride, MeNHPSF2, and MeNHPOF2, which were fully characterised. The addition of HPSF2 to alkenes took place at room temperature under the influence of U.V. light to give alkylphosphonothioic difluorides, RPSF2 (R = Et, Prn, Bun), which were fully characterised. Evidence is presented which suggests that the ease of the U.V. induced addition of a phosphorus-halide to an alkene depends on the strength of the P-X (X = F, Cl, Br) bonds in the latter compound. It proved possible to isolate and characterise 2-bromoethylphosphonic difluoride, BrC2H4POF2, from the reaction between ethylene and bromophosphoryl difluoride