The kinetics and products of a range of reactions between 14 different anions and phosphorus trifluoride were studied in a flowing afterglow apparatus. These reactions are best rationalized as proceeding via a mechanism involving initial attack by the anion (Nu−) at phosphorus to form an energized tetracoordinate anion intermediate [NuPF3]−, which either undergoes collisional stabilization with helium or undergoes fragmentation via loss of HF if the original anion contains an acidic proton(s). This study suggests that PF3 is a general and useful reagent for the gas-phase synthesis of a range of phosphorus containing anions with phosphorus–carbon, phosphorus–nitrogen, phosphorus–oxygen, phosphorus–silicon and phosphorus–sulfur bonds.
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References
1.
O'HairR.A.J., “Gas Phase Positive and Negative Ion Chemistry of Organophosphorus Compounds via Mass Spectrometric Techniques”, in The Chemistry of Organophosphorus Compounds—Volume 4, Ed by HartleyF.R., John Wiley & Sons, Chichester, Chapter 8, p. 731 (1996).
2.
GrabowskiJ.J.RoyP.D.LeoneR., J. Chem. Soc. Perkin Trans. II1627 (1988).
3.
AndersonD.R.DePuyC.H.FilleyJ.BierbaumV.M., J. Am. Chem. Soc.106, 6513 (1984).
LumR.C.GrabowskiJ.J., J. Am. Chem. Soc.114, 8619 (1992).
6.
LumR.C.GrabowskiJ.J., J. Am. Chem. Soc.114, 9663 (1992).
7.
MillerT.M.MillerA.E. StevensViggianoA. A.MorrisR.A.PaulsonJ.F., J. Chem. Phys.100, 7200 (1994).
8.
O'HairR.A.J.SheldonJ.C.BowieJ.H., J. Chem. Soc., Dalton Trans.2837 (1988).
9.
(a) McDonaldR.N.JonesM.T.ChowdhuryA.K., J. Am. Chem. Soc.113, 476 (1991); (b) McDonaldR.N.ChowdhuryA.K., J. Am. Chem. Soc.107, 4123 (1985); (c) McDonaldR.N.ChowdhuryA.K.SetserD.W., J. Am. Chem. Soc.102, 6491 (1980).
10.
SmithJ.D., M.S. Thesis, Kansas State University (1996).
11.
IkezoeY.MatsuokaS.TakebeM.ViggianoA., Gas Phase Ion-Molecule Reaction Rate Constants Through 1986.Ion Reaction Research Group, Tokyo (1987).
12.
Gas-phase acidities and other thermochemistry are taken from: (a) NIST Standard Reference Database 19B: NIST Negative Ion Energetics Database Version 2.07, Program written/data compilation by John E. Bartmess, Department of Chemistry, University of Tennessee, Knoxville, TN 37996–1600. This compilation is based on original data from: LiasS.G.BartmessJ.E.LiebmanJ.F.HolmesJ.L.LevinR.D.MallardW.G., “Gas-phase Ion and Neutral Thermochemistry”, J. Phys. Chem. Ref. DataVol. 17, Suppl. 1 (1988); (b) PilcherG., “Thermochemistry of Phosphorus (III) Compounds”, in The Chemistry of Organophosphorus Compounds—Volume 1, Ed by HartleyF.R., John Wiley & Sons, Chichester, Chapter 5, p. 127 (1990).
13.
(a) SuT.BowersM.T., Int. J. Mass Spectrom. Ion Phys.12, 347 (1973); (b) MillerK.J.SavchikJ.A., J. Am. Chem. Soc.101, 7206 (1979).
A reviewer has asked us to comment on the thermochemistry of the addition–elimination step (Equation 9). We have previously noted (Reference 1) that there is a dearth of reliable thermochemical information on phosphorus-containing anions. For example, even for one of the simplest cases (where HA− = HO−), there are three different values for the heat of formation of H2PO−: (i) −448 kJ mol−1 [(Reference 12(a)]; (ii) −887.7 kJ mol−1 (calculated from: The fluoride ion affinity of FP = O, FIA(FP = O) = 234.3 kJ mol−1 [Reference 4(b)]; ΔH0f (F−) = −249 kJ mol−1 [Reference 12(a)] and ΔH0f (FP = O) = −404.4 kJ mol−1 [Reference 12(b)] and (iii) <–962 kJ mol−1 [Reference 12(a)]. Using other thermochemistry (ΔH0f (HO−) = −137 kJ mol−1 [Reference 12(a)]; ΔH0f (F3P) = −958 kJ mol−1 [Reference 12(a)] and ΔH0f (HF) = −272.5 kJ mol−1 [Reference 12(a)]. This results in three quite different estimates for the enthalpy change of reaction 9 (where HA− = HO−): (i) +374.5 kJ mol−1; (ii) −65.2 kJ mol−1 and (iii) −139.5 kJ mol−1).
For previous chemical probes of “O” versus “C” reactivity of ambident enolate anions see: (a) BrickhouseM.D.SquiresR.R., J. Phys. Org. Chem.2, 389 (1989); (b) FreriksI.L.de KoningL.J.NibberingN.M.M., J. Am. Chem. Soc.113, 9119 (1991); (c) WladkowskiB.D.WilburJ.L.ZhongM.BraumanJ.I., J. Am. Chem. Soc.115, 8833 (1993).
18.
A reviewer has suggested a third possible type of structure for the adduct, viz. the fluroride ion–molecule complex shown as (C) in Scheme 1.
19.
We recognize the dangers of oversimplifying the picture since the prediction of the gas-phase acidity of a species (A–H) is complicated by the fact that the acidity is influenced by both the electron affinity of A and the homolytic bond dissociation energy of A–H. For a discussion with relevance to phosphorus species, see: BergerS.BraumanJ.I., J. Am. Chem. Soc.114, 4737 (1992).
20.
It is interesting to note that a SiF3 group enhances the gas-phase acidity of methane by over 200 kJ mol−1: AllisonC.E.McMahonT.B., J. Am. Chem. Soc.112, 1672 (1990).
21.
(a) CavellR.G., J. Chem. Soc.1992 (1964); (b) HarmanJ.S.SharpD.W.A., J. Chem. Soc. (A)1935 (1970).
