Phosphorine (

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

name: phosphinine) is a heavier element analog of

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

, containing a

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

atom instead of an aza- moiety. It is also called phosphabenzene and belongs to the

phosphaalkene Phosphaalkenes (IUPAC name: alkylidenephosphanes) are organophosphorus compounds with double bonds between carbon and phosphorus(III) with the formula R2C=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus. The ...

class. It is a colorless liquid that is mainly of interest in research. Phosphorine is an air-sensitive oil but is otherwise stable when handled using

air-free technique Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less comm ...

s (however, substituted derivatives can often be handled under air without risk of decomposition). In contrast,

silabenzene A silabenzene is a heteroaromatic compound containing one or more silicon atoms instead of carbon atoms in benzene. A single substitution gives silabenzene proper; additional substitutions give a disilabenzene (3 theoretical isomers), trisilabenz ...

, a related heavy-element analogue of benzene, is not only air- and moisture-sensitive but also thermally unstable without extensive steric protection.

History

The first phosphorine to be isolated is 2,4,6-triphenylphosphorine. It was synthesized by Gottfried Märkl in 1966 by condensation of the corresponding

pyrylium salt Pyrylium is a cation (positive ion) with formula , consisting of a six-membered ring of five carbon atoms, each with one hydrogen atom, and one positively charged oxygen atom. The bonds in the ring are conjugated as in benzene, giving it an aroma ...

and

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

or its equivalent ( P(CH₂OH)₃ and P(SiMe₃)₃).''G. Märkl'', 2,4,6-Triphenylphosphabenzol i
Angewandte Chemie 78, 907–908 (1966)
/ref> 500px, Synthesis of Triphenylphosphabenzene The (unsubstituted) parent phosphorine was reported by Arthur J. Ashe III in 1971. Ring-opening approaches have been developed from

phosphole Phosphole is the organic compound with the chemical formula ; it is the phosphorus analog of pyrrole. The term phosphole also refers to substituted derivatives of the parent heterocycle. These compounds are of theoretical interest but also serve a ...

Structure, bonding, and properties

Structural studies by electron diffraction reveal that phosphorine is a planar

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

compound with 88% of aromaticity of that of

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

. Potentially relevant to its high aromaticity are the well matched

electronegativities Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...

of phosphorus (2.1) and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

(2.5). The P–C

bond length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...

is 173 pm and the C–C bond lengths center around 140 pm and show little variation. Although phosphorine and

are structurally similar, phosphorines are far less basic. The p''K''_a of C₅H₅PH⁺ and C₅H₅NH⁺ are respectively −16.1 and +5.2.François Mathey "Phosphorus Heterocycles" in Modern Heterocyclic Chemistry, First Edition, edited by Julio Álvarez-Builla, Juan José Vaquero, José Barluenga, Wiley-VCH, Weinheim, 2011. .

Methyllithium Methyllithium is the simplest organolithium reagent with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in so ...

adds to phosphorus in phosphorine whereas it adds to the 2-position of pyridine.Ashe III, Arthur J.; Smith, Timothy W. "The reaction of phosphabenzene, arsabenzene and stibabenzene with methyllithium." Tetrahedron Letters 1977, volume 18, pp. 407–410. Phosphorine undergoes electrophilic substitution reactions like ordinary

compounds:

bromination In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, ...

acylation In chemistry, acylation (or alkanoylation) is the chemical reaction in which an acyl group () is added to a compound. The compound providing the acyl group is called the acylating agent. Because they form a strong electrophile when treated with ...

, and so on.

Coordination chemistry

Coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

es bearing phosphorine as a igandare known. Phosphorines can bind to metals through phosphorus center. Complexes of the diphospha analogue of

2,2′-bipyridine 2,2′-Bipyridine (bipy or bpy, pronounced ) is an organic compound with the formula C10H8N2. This colorless solid is an important isomer of the bipyridine family. It is a bidentate chelating ligand, forming complexes with many transition metals ...

are known. Phosphorines also form pi-complexes, illustrated by V(''η''⁶-C₅H₅P)₂.

References

* {{cite book , title = A Guide to Organophosphorus Chemistry , author = Quin, L. D. , publisher = Wiley-Interscience , year = 2000 , isbn = 978-0-471-31824-8 Phosphorus heterocycles Six-membered rings Substances discovered in the 1970s

History

Structure, bonding, and properties

Coordination chemistry

See also

References