Bis(triphenylphosphine)iminium chloride
Bis(triphenylphosphine)iminium chloride is the chemical compound with the formula [((C6H5)3P)2N]Cl, often abbreviated [(Ph3P)2N]Cl, where Ph is phenyl C6H5, or even abbreviated [PPN]Cl or [PNP]Cl or PPNCl or PNPCl, where PPN or PNP stands for (Ph3P)2N. This colorless salt is a source of the [(Ph3P)2N]+ cation (abbreviated PPN+ or PNP+), which is used as an unreactive and weakly coordinating cation to isolate reactive anions. [(Ph3P)2N]+ is a phosphazene.
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| Names | |
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| Preferred IUPAC name
Hexaphenyl-1λ5-diphosphaz-1-en-3-ium chloride | |
| Other names
PNP chloride
PPN chloride Bis(triphenylphosphine)iminium chloride Bis(triphenylphosphoranylidene)iminium chloride Bis(triphenylphosphoranylidene)ammonium chloride Hexaphenyldiphosphazenium chloride Selectophore | |
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.040.139 |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| [((C6H5)3P)2N]Cl | |
| Molar mass | 574.03 g/mol |
| Appearance | colourless solid |
| Melting point | 260 to 262 °C (500 to 504 °F; 533 to 535 K) |
| moderate | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H315, H319, H332, H335 | |
| P261, P264, P271, P280, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501 | |
| Related compounds | |
Related compounds
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Tetraphenylarsonium 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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Synthesis and structure
edit[(Ph3P)2N]Cl is prepared in two steps from triphenylphosphine Ph3P:[1]
- Ph3P + Cl2 → Ph3PCl2
This triphenylphosphine dichloride Ph3PCl2 is related to phosphorus pentachloride PCl5. Treatment of this species with hydroxylamine in the presence of Ph3P results in replacement of the two single P–Cl bonds in Ph3PCl2 by one double P=N bond:
- 2 Ph3PCl2 + NH2OH·HCl + Ph3P → [(Ph3P)2N]Cl + 4HCl + Ph3PO
Triphenylphosphine oxide Ph3PO is a by-product.
Bis(triphenylphosphine)iminium chloride is described as [(Ph3P)2N]+Cl−. The structure of the bis(triphenylphosphine)iminium cation [(Ph3P)2N]+ is [Ph3P=N=PPh3]+. The P=N=P angle in the cation is flexible, ranging from ~130 to 180° depending on the salt. Bent and linear forms of the P=N=P connections have been observed in the same unit cell.[2] The same shallow potential well for bending is observed in the isoelectronic species bis(triphenylphosphoranylidene)methane, Ph3P=C=PPH3, as well as the more distantly related molecule carbon suboxide, O=C=C=C=O. For the solvent-free chloride salt [(Ph3P)2N]Cl, the P=N=P bond angle was determined to be 133°.[3] The two P=N bonds are equivalent, and their length is 1.597(2) Å.
Use as reagent
editIn the laboratory, [(Ph3P)2N]Cl is the main precursor to [(Ph3P)2N]+ salts. Using salt metathesis reactions, nitrite, azide, and other small inorganic anions can be obtained with [(Ph3P)2N]+ cations. The resulting salts [(Ph3P)2N]+NO−2, [(Ph3P)2N]+N−3, etc. are soluble in polar organic solvents.
[(Ph3P)2N]+ 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 [(Ph3P)2N]+ forms salts that are more air-stable than salts with smaller cations such as those containing quaternary ammonium cation [NR4]+, or alkali metal cations. This effect is attributed to the steric shielding provided by this voluminous cation. Illustrative [(Ph3P)2N]+ salts of reactive anions include [(Ph3P)2N]+[HFe(CO)4]−, [(Ph3P)2N]+[Co(CO)4]−, ([(Ph3P)2N]+)2[M2(CO)10]2+ (M = Cr, Mo, W), and [(Ph3P)2N]+[Fe(CO)3(NO)]−.[1] The role of ion pairing in chemical reactions is often clarified by examination of the related salt derived from [(Ph3P)2N]+.
Related cations
editA phosphazenium cation related to [(Ph3P)2N]+ is [(((CH3)2N)3P)2N]+.[4]
References
edit- ^ a b Ruff, J.K.; Schlientz, W.J. (1974). "μ-Nitridobis(triphenylphosphorus)(l+) ("PPN") Salts with Metal Carbonyl Anions". Inorganic Syntheses. Vol. 15. pp. 84–90. doi:10.1002/9780470132463.ch19. ISBN 9780470132463.
{{cite book}}:|journal=ignored (help) - ^ Hardy GE, Zink JI, Kaska WC, Baldwin JC (December 1978). "Structure and triboluminescence of polymorphs of hexaphenylcarbodiphosphorane". Journal of the American Chemical Society. 100 (25): 8001–8002. doi:10.1021/ja00493a035.
- ^ Knapp C, Uzun R (November 2010). "Solvate-free bis-(triphenylphosphine)iminium chloride". Acta Crystallographica Section E. 66 (Pt 12): o3185. doi:10.1107/S1600536810046325. PMC 3011587. PMID 21589480.
- ^ Schwesinger, Reinhard (2001). "1,1,1,3,3,3-Hexakis(dimethylamino)-1λ5,3λ5-diphosphazenium fluoride". e-EROS Encyclopedia of Reagents for Organic Synthesis. pp. 1–2. doi:10.1002/047084289X.rh014m. ISBN 0471936235.