Bis(triphenylphosphine)iminium chloride

Bis(triphenylphosphine)iminium chloride

Names
IUPAC name μ-nitrido-Bis(triphenylphosphorus) chloride
Other names PPN chloride Bis(triphenylphosphine)iminium chloride Bis(triphenylphosphoranylidene)iminium chloride Bis(triphenylphosphoranylidene)ammonium chloride Hexaphenyldiphosphazenium chloride Selectophore
Identifiers
CAS Number	21050-13-5 Y
3D model (Jmol)	Interactive image
ChemSpider	2300634 Y
ECHA InfoCard	100.040.139
PubChem	3036656
InChI InChI=1S/C36H30NP2.ClH/c1-7-19-31(20-8-1)38(32-21-9-2-10-22-32,33-23-11-3-12-24-33)37-39(34-25-13-4-14-26-34,35-27-15-5-16-28-35)36-29-17-6-18-30-36;/h1-30H;1H/q+1;/p-1 Y Key: LVRCYPYRKNAAMX-UHFFFAOYSA-M Y InChI=1/C36H30NP2.ClH/c1-7-19-31(20-8-1)38(32-21-9-2-10-22-32,33-23-11-3-12-24-33)37-39(34-25-13-4-14-26-34,35-27-15-5-16-28-35)36-29-17-6-18-30-36;/h1-30H;1H/q+1;/p-1 Key: LVRCYPYRKNAAMX-REWHXWOFAO
SMILES [Cl-].N([P+](c1ccccc1)(c2ccccc2)c3ccccc3)=P(c4ccccc4)(c5ccccc5)c6ccccc6
Properties
Chemical formula	C36H30ClNP2
Molar mass	574.03 g/mol
Appearance	colourless solid
Density	?? g/cm3, solid
Melting point	260 to 262 °C (500 to 504 °F; 533 to 535 K)
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 otherwise noted, 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

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^––P⁺Ph₃, which explains non-linear arrangement of P-N-P moiety owing to sp³-hybridization of the nitrogen center. Alternative depiction Ph₃P=N=PPh₃⁺ would imply sp-hybridization at N-atom and thus linear structure which is not the case.

Applications

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

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.