Other Fluorophosphines

Difluorophosphine, first reported in 1965, is a relatively stable gas [b.p. (extrapolated) —64.6°C, m.p. —124.2° to —123.6°C], which is formed in about 55% yield by reacting equal amounts of hydrogen iodide and difluoroiodophosphine (Section IV) in the presence of mercury 276). It has been suggested 275) that tetrafluorodiphosphine 

P2F4 (Section VII,B) is a precursor in this synthesis. The yield may be 

It is interesting to note that although PF4H can be decomposed to HF and PFg it has not so far been possible to prepare PF2H from PF3H2 27). 

Difluorophosphine is less that 5% decomposed at room temperature and saturation pressure over a period of 5 hours, and thus contrasts markedly with difluoroamine (NF2II) which is very unstable. 

Vapor pressure measurements lead to a Trouton constant of 24.7 cal deg mole suggesting that association occurs in the condensed phase. Gas phase molecular weight measurements, however, indicate that the vapor is monomeric 276). 

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Clark and co-workers have shown that trifluorophosphine can replace all the CO groups from certain metal carbonyl complexes (56, 58, 59). Other fluorophosphines behave similarly, the reactions usually being thermally or photochemically induced (320, 57, 121, 284, 287, 61). In the case of HCo(CO)4, however, substitution by PFg occurs rapidly and spontaneously even at —20°C (320). 

From Other Fluorophosphine-Transition Metal Complexes... 

Tetelbaum et al. (315) have suggested that a correlation exists between Sp for compounds of the type XPF2 (where the group X is alkyl, aryl, or halogenoalkyl) and the Taft a parameter for X. While it is true that the lowest-fleld chemical shifts (—200 to —250 ppm) occur for the alkyl derivatives, values for other fluorophosphines sometimes show irregular variations (Tables II-VI) even within fairly closely related compounds. 

In the course of a study of the formation of fluorophosphoranes from chloro-phosphines (22) we observed one exception in the compound chloromethyldi-chlorophosphine, which reacted smoothly with antimony trifluoride to give the flammable fluorophosphine, C1CH2PF2, under conditions where many other chloro-phosphines were invariably converted into fluorophosphoranes. As this fluorophosphine is readily available, its interaction with a metal carbonyl derivative was studied, and cycloheptatriene molybdenum tricarbonyl, obtained from the reaction of molybdenum hexacarbonyl with cycloheptatriene (I, 2), was chosen as a starting compound. 

Direct Synthesis from the Metals. The first zerovalent compound prepared, namely Ni(CO)4, was first obtained by this method—i.e., from active nickel and carbon monoxide at ordinary temperature and pressure mi)- Though not largely applicable, this method can be used in some other cases. K4[Ni(CN)4] could be prepared from metallic nickel and potassium cyanide (205), while some chloro- (156), bromo- 125) and fluorophosphine (118) and some tertiary diphosphine (44) could react with metallic nickel to give the tetracoordinated nickel(O) derivatives. 

Fluorophosphines are tervalent phosphorus compounds containing phosphorus-fluorine bonds and they often show markedly different chemical behavior compared with other halogenophosphines. This article is mainly concerned with recent advances in the chemistry of derivatives of PF 3 of the type PF3 X , with particular reference to (a) synthesis of new structural types, (6) the role of fluorophosphines as ligands, particularly in transition metal complexes, and (c) nuclear magnetic resonance (NMR) studies. 

On the other hand, when the group R contains an electron-withdrawing substituent, fluorination affords only the corresponding tervalent fluorophosphine (229),... 

On the other hand, Sheluchenko et al. (301) found no simple correlation between Sp and the inductive effect of the X group for a series of fluorophosphines of the type RPFX (X = OR, NR2, SR, Cl), and while the main criterion for determining the phosphorus shift seems to be the atoms to which phosphorus is bonded, at present there is no quantitative understanding of the P shift data summarized in Tables II-VI. 

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