Bis(triphenylphosphine)iminium chloride is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula , often abbreviated , where Ph is

phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...

, or even abbreviated PNl or NPl or PPNCl or PNPCl, where PPN or PNP stands for . This

color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

less salt is a source of the cation (abbreviated or ), which is used as an unreactive and weakly coordinating cation to isolate reactive anions. is a

phosphazene Phosphazenes refer to various classes of organophosphorus compounds featuring phosphorus(V) with a double bond between P and N. One class of phosphazenes have the formula . These phosphazenes are also known as iminophosphoranes and phosphine imides ...

Synthesis and structure

is prepared in two steps from

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a l ...

: : This

triphenylphosphine dichloride Triphenylphosphine dichloride is an organophosphorus compound with the chemical formula , often abbreviated as , where Ph is phenyl. It is a chlorinating agent widely used in organic chemistry. Applications include the conversion of alcohols and ...

is related to

phosphorus pentachloride Phosphorus pentachloride is the chemical compound with the formula . It is one of the most important phosphorus chlorides/oxychlorides, others being and . finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, althoug ...

. Treatment of this species with

hydroxylamine Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula . The compound exists as hygroscopic colorless crystals.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Prof ...

in the presence of results in replacement of the two single P–Cl bonds in by one double P=N bond: :

Triphenylphosphine oxide Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula , also written as or (Ph = ). It is one of the more common phosphine oxides. This colourless crystalline compound is a common but potentially u ...

is a by-product. Bis(triphenylphosphine)iminium chloride is described as . The structure of the bis(triphenylphosphine)iminium chloride is . 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. The same shallow potential well for bending is observed in the isoelectronic species bis(triphenylphosphoranylidene)methane, , as well as the more distantly related molecule

carbon suboxide Carbon suboxide, or tricarbon dioxide, is an organic, oxygen-containing chemical compound with formula and structure . Its four cumulative double bonds make it a cumulene. It is one of the stable members of the series of linear oxocarbons , wh ...

, . For the solvent-free chloride salt , the P=N=P bond angle was determined to be 133°. The two P=N bonds are equivalent, and their length is 1.597(2) Å. PPN-cation-from-xtal-CM-3D-ellipsoids

Use as reagent

In the laboratory, is the main precursor to salts. Using salt metathesis reactions,

nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

azide In chemistry, azide (, ) is a linear, polyatomic anion with the formula and structure . It is the conjugate base of hydrazoic acid . Organic azides are organic compounds with the formula , containing the azide functional group. The dominant ...

, and other small inorganic anions can be obtained with cations. The resulting salts , , etc. are soluble in polar organic solvents. 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 forms salts that are more air-stable than salts with smaller cations such as those containing

quaternary ammonium In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure , where R is an alkyl group, an aryl group or organyl group. Unlike the ammonium ion () and the primary, secondary, o ...

cation , or

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

cations. This effect is attributed to the steric shielding provided by this voluminous cation. Illustrative salts of reactive anions include , , (M = Cr, Mo, W), and . The role of

ion pair In chemistry, ion association is a chemical reaction whereby ions of opposite electric charge come together in solution to form a distinct chemical entity. Ion associates are classified, according to the number of ions that associate with each ...

ing in chemical reactions is often clarified by examination of the related salt derived from .

Related cations

A phosphazenium cation related to is .

References

{{reflist Organophosphorus compounds Chlorides Phosphazenes Phenyl compounds