Editing Phosphorine

{{distinguish|phosphine}}
{{Chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 464205305
|ImageFileL1 = Phosphorine-skeletal.svg
|ImageFileL1_Ref = {{chemboximage|correct|??}}
|ImageSizeL1 = 121
|ImageNameL1 = Kekulé skeletal formula of phosphorine
|ImageFileR1 = Phosphabenzene-Spartan-MP2-3D-balls.png
|ImageFileR1_Ref = {{chemboximage|correct|??}}
|ImageSizeR1 = 121
|ImageNameR1 = Aromatic ball and stick model of phosphorine
|PIN = Phosphinine<ref name=iupac2013>{{bluebook2013}}  p.&nbsp;47.</ref>
|OtherNames = Phosphabenzene
|Section1 = {{Chembox Identifiers 
|CASNo = 289-68-9
|CASNo_Ref = {{cascite|correct|PubChem}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = A8TY55D4JJ
|PubChem = 123046
|ChemSpiderID = 109668
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|MeSHName = Phosphinine
|SMILES = C1=CC=PC=C1
|StdInChI = 1S/C5H5P/c1-2-4-6-5-3-1/h1-5H
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|InChI = 1/C5H5P/c1-2-4-6-5-3-1/h1-5H
|StdInChIKey = UNQNIRQQBJCMQR-UHFFFAOYSA-N
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|InChIKey = UNQNIRQQBJCMQR-UHFFFAOYAZ
}}
| Section2 = {{Chembox Properties
| C=5 | H=5 | P=1 
| AtmosphericOHRateConstant = 
| Appearance     = Colorless liquid
| BoilingPt      = 
| BoilingPtC     = 93
| BoilingPt_ref  = <ref name="bp">{{cite journal |author1=Aleksandr Savateev |author2=Yurii Vlasenko |author3=Nataliya Shtil |author4=Aleksandr Kostyuk |title=Reduction of λ5-Phosphinines |journal=European Journal of Inorganic Chemistry |date=2016 |issue=5 |pages=628-632 |doi=10.1002/ejic.201500856 |language=en}}</ref>
| BoilingPt_notes= 
| Density        = 
| HenryConstant  = 
| LogP           = 
| MeltingPt      = 
| MeltingPtC     = 
| MeltingPt_ref  = 
| MeltingPt_notes= 
| pKa            = -16 (conjugate acid)
| pKb            = 
| Solubility     = 
| SolubleOther   = 
| Solvent        = 
| VaporPressure  = 
}}
| Section3 = {{Chembox Related
| OtherFunction_label = -ines
| OtherFunction = {{ubl|[[Pyridine]]|[[Arsabenzene]]|[[Silabenzene]]}}
|OtherCompounds = [[Phosphole]]
}}
}}

'''Phosphorine''' ([[IUPAC]] name: '''phosphinine''') is a heavier [[Chemical element|element]] analog of [[pyridine]], containing a [[phosphorus]] atom instead of an [[aza-]] moiety. It is also called '''phosphabenzene''' and belongs to the [[phosphaalkene]] class. It is a colorless liquid that is mainly of interest in research.

Phosphorine is an air-sensitive oil<ref name="Ashe" /> but is otherwise stable when handled using [[air-free technique]]s (however, substituted derivatives can often be handled under air without risk of decomposition).<ref name=":0" /><ref>{{Cite journal|last1=Newland|first1=R. J.|last2=Wyatt|first2=M. F.|last3=Wingad|first3=R. L.|last4=Mansell|first4=S. M.|date=2017|title=A ruthenium(II) bis(phosphinophosphinine) complex as a precatalyst for transfer-hydrogenation and hydrogen-borrowing reactions|journal=Dalton Transactions|language=en|volume=46|issue=19|pages=6172–6176|doi=10.1039/C7DT01022B|pmid=28436519|issn=1477-9226|doi-access=free|hdl=1983/8ceafa01-697c-4055-bd9f-3bfcb60d93f2|hdl-access=free}}</ref> In contrast, [[silabenzene]], 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]] and [[phosphine]] or its equivalent ( P(CH<sub>2</sub>OH)<sub>3</sub> and P(SiMe<sub>3</sub>)<sub>3</sub>).<ref name=":0">''G. Märkl'', 2,4,6-Triphenylphosphabenzol in [http://onlinelibrary.wiley.com/doi/10.1002/ange.19660781817/abstract Angewandte Chemie '''78''', 907–908 (1966)]</ref>

[[file:Synthesis Triphenylphosphabenzene.svg|500px|Synthesis of Triphenylphosphabenzene]]

The (unsubstituted) parent phosphorine was reported by Arthur J. Ashe III in 1971 by the reaction of 1,4-dihydro-1,1 dibutylstannabenzene and [[phosphorus tribromide]].<ref name="Ashe">{{ cite journal | last1 = Ashe | first1 = A. J. | title = Phosphabenzene and Arsabenzene | journal = [[Journal of the American Chemical Society]] | year = 1971 | volume = 93 | issue = 13 | pages = 3293–3295  | doi = 10.1021/ja00742a038 }}</ref><ref>{{Greenwood&Earnshaw2nd | page = 544}}</ref> Ring-opening approaches have been developed from [[phosphole]]s.<ref name=Mathey/>

==Structure, bonding, and properties==
Structural studies by electron diffraction reveal that phosphorine is a planar [[aromatic]] compound with 88% of aromaticity of that of [[benzene]]. Potentially relevant to its high aromaticity are the well matched [[electronegativity|electronegativities]] of phosphorus (2.1) and [[carbon]] (2.5). The P–C [[bond length]] is 173&nbsp;[[picometer|pm]] and the C–C bond lengths center around 140&nbsp;pm  and show little variation.<ref>László Nyulászi "Aromaticity of Phosphorus Heterocycles" Chem. Rev., 2001, volume 101, pp 1229–1246. {{doi|10.1021/cr990321x}}</ref>
{|style="margin: 1em auto 1em auto;"
|[[File:Bond lengths of group 15 heterobenzenes and benzene.svg|center|thumb|620px|Bond lengths and angles of benzene, [[pyridine]], phosphorine, [[arsabenzene]], [[stibabenzene]] and [[bismabenzene]]]]
|}

Although phosphorine and [[pyridine]] are structurally similar, phosphorines are far less basic. The p''K''<sub>a</sub> of C<sub>5</sub>H<sub>5</sub>PH<sup>+</sup> and C<sub>5</sub>H<sub>5</sub>NH<sup>+</sup> are respectively −16.1 and +5.2.  The P-oxides are extremely unstable, rapidly adding nucleophiles to a species tetracoordinate at phosphorus.  Strongly backbonding Lewis acids (e.g. [[tungsten pentacarbonyl]]) can stabilize a [[dative bond]] from phosphorus.<ref name=Mathey>Mathey, François (2011).  "Phosphorus Heterocycles" in ''Modern Heterocyclic Chemistry'', 1st ed., edited by Álvarez-Builla, Julio; José&nbsp;Vaquero, Juan; and Barluenga, José.  Weinheim: Wiley-VCH. §23.3.  {{doi|10.1002/9783527637737.ch23}}.</ref>  

Both [[electrophile]]s and strong, hard [[nucleophile]]s preferentially attack at phosphorus, but the ring aromaticity is sufficiently weak that the result is an [[addition reaction]], and not aromatic substitution.<ref name=Mathey/>  Thus for example [[methyllithium]] adds to phosphorus in phosphorine whereas it adds to the 2-position of pyridine.<ref>Ashe III, Arthur J.; Smith, Timothy W. "The reaction of phosphabenzene, arsabenzene and stibabenzene with methyllithium." Tetrahedron Letters 1977, volume 18, pp. 407–410. {{doi|10.1016/S0040-4039(01)92651-6}}</ref>  Halophosphorines do undergo noble-metal- or [[zirconocene]]-catalyzed substitution, and λ<sup>5</sup>-phosphorines exhibit [[electrophilic aromatic substitution|a much more traditional substitution chemistry]].<ref name=Mathey/>  

Unlike [[arsabenzene]], phosphorine rarely participates in [[Diels-Alder]]-type cycloadditions; when it does, the coupling partner must be an extremely electron-poor alkyne.  Phosphorine ''complexes'' are tolerable Diels-Alder reactants.<ref name=Mathey/>  

===Coordination chemistry===
[[Coordination complex]]es bearing phosphorine as a [[ligand]] are known. Phosphorines can bind to metals through phosphorus center.  Complexes of the diphospha analogue of [[2,2′-bipyridine]] are known. Phosphorines also form pi-complexes, illustrated by V(''η''<sup>6</sup>-C<sub>5</sub>H<sub>5</sub>P)<sub>2</sub>.<ref name=Mathey/>

== See also ==
* Six-membered aromatic rings with one carbon replaced by an element from another group: [[borabenzene]], [[silabenzene]], [[germabenzene]], [[stannabenzene]], [[pyridine]], phosphorine, [[arsabenzene]], [[stibabenzene]], [[bismabenzene]], [[pyrylium]], [[thiopyrylium]], [[selenopyrylium]], [[telluropyrylium]]

== References ==
{{Reflist}}
* {{cite book | title = A Guide to Organophosphorus Chemistry | author = Quin, L. D. | publisher = Wiley-Interscience | year = 2000 | isbn = 978-0-471-31824-8}}

[[Category:Phosphorus heterocycles]]
[[Category:Six-membered rings]]
[[Category:Substances discovered in the 1970s]]