Bis(triphenylphosphine)iminium chloride

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Bis(triphenylphosphine)iminium chloride
PPNCl.png
Identifiers
CAS number 21050-13-5
PubChem 3036656
ChemSpider 2300634 YesY
Jmol-3D images Image 1
Properties
Molecular formula C36H30ClNP2
Molar mass 574.03 g/mol
Appearance colourless solid
Density  ?? g/cm3, solid
Melting point 260-2 °C
Solubility in water moderate
Hazards
R-phrases 36/37/38
S-phrases 26-36
Related compounds
Related compounds Tetraphenylarsonium chloride
Tetrabutylammonium chloride
tetrabutylammonium chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Bis(triphenylphosphine)iminium chloride is the chemical compound with the formula [(C6H5)3P)2N]Cl, often written [(Ph3P)2N]Cl and abbreviated PPNCl. This colorless salt is a source of the PPN+ cation, which is used to isolate reactive anions. PPN+ is a phosphazene.

Synthesis and structure[edit]

PPNCl is prepared in two steps from triphenylphosphine:[1]

Ph3P + Cl2 → Ph3PCl2

This triphenylphosphine dichloride is related to phosphorus pentachloride. Treatment of this species with hydroxylamine in the presence of Ph3P results in replacement of the P-Cl bonds by P=N bonds:

2 Ph3PCl2 + NH2OH·HCl + Ph3P → {[Ph3P]2N}Cl + 4HCl + Ph3PO

In PPN+ salts, P-N bond lengths are equivalent, 1.58 Å. The cation is bent at the central nitrogen, and has no inversion centre. Its connectivity is indicated by Ph3P=N=PPh3+.

thermal ellipsoid model the bis(triphenylphosphine)iminium cation

Applications[edit]

In the laboratory, PPN chloride is the main precursor to PPN+ salts. Using salt metathesis reactions, nitrite, azide, and other small inorganic anions can be obtained with PPN+ cations. The resulting salts PPNNO2, PPNN3 etc. are soluble in polar organic solvents.

PPN+ forms crystalline salts with a range of anions that are otherwise difficult to crystallize. Its effectiveness is partially attributable to its rigidity, reflecting the presence of six phenyl rings. Often PPN+ forms salts that are more air-stable than salts with smaller cations such as those containing quaternary ammonium or alkali metal cations. This effect is attributed to the steric shielding provided by this voluminous cation. Illustrative PPN+ salts of reactive anions include PPN[HFe(CO)4], PPN[Co(CO)4], and PPN[Fe(CO)3NO]. The role of ion pairing in chemical reactions is often clarified by examination of the related salt derived from PPN+.

References[edit]

  1. ^ J. K. Ruff; W. J. Schlientz; R. E. Dessy; J. M. Malm; G. R. Dobson; M. N. Memering (1974). "μ-nitrido-Bis(triphenylphosphorus)(1+ ("PPN") Salts with Metal Carbonyl Anions". Inorg. Synth. 15: 84–90. doi:10.1002/9780470132463.ch19.