Bis(triphenylphosphine)iminium chloride#Synthesis and structure
{{chembox
| Watchedfields = changed
| verifiedrevid = 447561260
| Name =
| ImageFile = PPNCl.png
| ImageName =
| PIN = Hexaphenyl-1λ5-diphosphaz-1-en-3-ium chloride
| OtherNames = PNP chloride
PPN chloride
Bis(triphenylphosphine)iminium chloride
Bis(triphenylphosphoranylidene)iminium chloride
Bis(triphenylphosphoranylidene)ammonium chloride
Hexaphenyldiphosphazenium chloride
Selectophore
| SystematicName =
| Section1 = {{Chembox Identifiers
| SMILES = [Cl-].N([P+](c1ccccc1)(c2ccccc2)c3ccccc3)=P(c4ccccc4)(c5ccccc5)c6ccccc6
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 2300634
| PubChem = 3036656
| EC_number = 244-170-6
| 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
| InChIKey = LVRCYPYRKNAAMX-REWHXWOFAO
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 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
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = LVRCYPYRKNAAMX-UHFFFAOYSA-M
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 21050-13-5
}}
| Section2 = {{Chembox Properties
| Formula = {{chem2|[((C6H5)3P)2N]Cl}}
| MolarMass = 574.03 g/mol
| Appearance = colourless solid
| Solubility = moderate
| MeltingPtC = 260 to 262
| MeltingPt_notes =
}}
| Section3 =
| Section4 =
| Section5 =
| Section6 =
| Section7 = {{Chembox Hazards
| GHSPictograms = {{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|315|319|332|335}}
| PPhrases = {{P-phrases|261|264|271|280|302+352|304+312|304+340|305+351+338|312|321|332+313|337+313|362|403+233|405|501}}
}}
| Section8 = {{Chembox Related
| OtherCompounds = Tetraphenylarsonium chloride
Tetrabutylammonium chloride}}
}}
Bis(triphenylphosphine)iminium chloride is the chemical compound with the formula {{chem2|[((C6H5)3P)2N]Cl}}, often abbreviated {{chem2|[(Ph3P)2N]Cl}}, where Ph is phenyl {{chem2|C6H5}}, or even abbreviated [PPN]Cl or [PNP]Cl or PPNCl or PNPCl, where PPN or PNP stands for {{chem2|(Ph3P)2N}}. This colorless salt is a source of the {{chem2|[(Ph3P)2N]+}} cation (abbreviated {{chem2|PPN+}} or {{chem2|PNP+}}), which is used as an unreactive and weakly coordinating cation to isolate reactive anions. {{chem2|[(Ph3P)2N]+}} is a phosphazene.
Synthesis and structure
{{chem2|[(Ph3P)2N]Cl}} is prepared in two steps from triphenylphosphine {{chem2|Ph3P}}:{{cite book | last1 = Ruff|first1=J.K.|last2=Schlientz|first2=W.J. |title=Inorganic Syntheses |chapter=μ-Nitridobis(triphenylphosphorus)(l+) ("PPN") Salts with Metal Carbonyl Anions | journal = Inorg. Synth. | volume = 15 | year = 1974 | pages = 84–90 | doi = 10.1002/9780470132463.ch19|isbn=9780470132463}}
:{{chem2|Ph3P + Cl2 → Ph3PCl2}}
This triphenylphosphine dichloride {{chem2|Ph3PCl2}} is related to phosphorus pentachloride {{chem2|PCl5}}. Treatment of this species with hydroxylamine in the presence of {{chem2|Ph3P}} results in replacement of the two single P–Cl bonds in {{chem2|Ph3PCl2}} by one double P=N bond:
:{{chem2|2 Ph3PCl2 + NH2OH*HCl + Ph3P → [(Ph3P)2N]Cl + 4HCl + Ph3PO}}
Triphenylphosphine oxide {{chem2|Ph3PO}} is a by-product.
Bis(triphenylphosphine)iminium chloride is described as {{chem2|[(Ph3P)2N]+Cl-}}. The structure of the bis(triphenylphosphine)iminium chloride {{chem2|[(Ph3P)2N]+Cl-}} is {{chem2|[Ph3P\dN\dPPh3]+Cl-}}. 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.{{cite journal|last1=Hardy|first1=Gordon E.|last2=Zink|first2=Jeffrey I.|last3=Kaska|first3=W. C.|last4=Baldwin|first4=J. C. | name-list-style = vanc |date= December 1978|title=Structure and triboluminescence of polymorphs of hexaphenylcarbodiphosphorane |journal=Journal of the American Chemical Society |volume=100|issue=25|pages=8001–8002|doi=10.1021/ja00493a035 }} The same shallow potential well for bending is observed in the isoelectronic species bis(triphenylphosphoranylidene)methane, {{chem2|Ph3P\dC\dPPH3}}, as well as the more distantly related molecule carbon suboxide, {{chem2|O\dC\dC\dC\dO}}. For the solvent-free chloride salt {{chem2|[(Ph3P)2N]Cl}}, the P=N=P bond angle was determined to be 133°.{{cite journal | vauthors = Knapp C, Uzun R | title = Solvate-free bis-(triphenylphosphine)iminium chloride | journal = Acta Crystallographica Section E | volume = 66 | issue = Pt 12 | pages = o3185 | date = November 2010 | pmid = 21589480 | pmc = 3011587 | doi = 10.1107/S1600536810046325 }} The two P=N bonds are equivalent, and their length is 1.597(2) Å.
Use as reagent
In the laboratory, {{chem2|[(Ph3P)2N]Cl}} is the main precursor to {{chem2|[(Ph3P)2N]+}} salts. Using salt metathesis reactions, nitrite, azide, and other small inorganic anions can be obtained with {{chem2|[(Ph3P)2N]+}} cations. The resulting salts {{chem2|[(Ph3P)2N]+NO2-}}, {{chem2|[(Ph3P)2N]+N3-}}, etc. are soluble in polar organic solvents.
{{chem2|[(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 {{chem2|[(Ph3P)2N]+}} forms salts that are more air-stable than salts with smaller cations such as those containing quaternary ammonium cation {{chem2|[NR4]+}}, or alkali metal cations. This effect is attributed to the steric shielding provided by this voluminous cation. Illustrative {{chem2|[(Ph3P)2N]+}} salts of reactive anions include {{chem2|[(Ph3P)2N]+[HFe(CO)4]-}}, {{chem2|[(Ph3P)2N]+[Co(CO)4]-}}, {{chem2|([(Ph3P)2N]+)2[M2(CO)10](2+)}} (M = Cr, Mo, W), and {{chem2|[(Ph3P)2N]+[Fe(CO)3(NO)]-}}. The role of ion pairing in chemical reactions is often clarified by examination of the related salt derived from {{chem2|[(Ph3P)2N]+}}.
Related cations
A phosphazenium cation related to {{chem2|[(Ph3P)2N]+}} is {{chem2|[(((CH3)2N)3P)2N]+}}.{{cite encyclopedia|author=Schwesinger, Reinhard|title=1,1,1,3,3,3-Hexakis(dimethylamino)-1λ5,3λ5-diphosphazenium fluoride|encyclopedia=e-EROS Encyclopedia of Reagents for Organic Synthesis|year=2001|pages=1–2|doi=10.1002/047084289X.rh014m|isbn=0471936235}}