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| Names | |||
|---|---|---|---|
| Preferred IUPAC name Phosphinine[1] | |||
| Other names Phosphabenzene | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChemSpider |
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| MeSH | Phosphinine | ||
| UNII | |||
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| Properties | |||
| C5H5P | |||
| Molar mass | 96.069 g·mol−1 | ||
| Related compounds | |||
Related -ines | |||
Related compounds | Phosphole | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Phosphorine (IUPAC name:phosphinine) is a heavierelement analog ofpyridine, containing aphosphorus atom instead of anaza- moiety. It is also calledphosphabenzene and belongs to thephosphaalkene class. It is a colorless liquid that is mainly of interest in research.
Phosphorine is an air-sensitive oil[2] but is otherwise stable when handled usingair-free techniques (however, substituted derivatives can often be handled under air without risk of decomposition).[3][4] 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.
The first phosphorine to be isolated is 2,4,6-triphenylphosphorine. It was synthesized by Gottfried Märkl in 1966 by condensation of the correspondingpyrylium salt andphosphine or its equivalent ( P(CH2OH)3 and P(SiMe3)3).[3]
The (unsubstituted) parent phosphorine was reported by Arthur J. Ashe III in 1971.[2][5] Ring-opening approaches have been developed fromphospholes.[6]
Structural studies by electron diffraction reveal that phosphorine is a planararomatic compound with 88% of aromaticity of that ofbenzene. Potentially relevant to its high aromaticity are the well matchedelectronegativities of phosphorus (2.1) andcarbon (2.5). The P–Cbond length is 173 pm and the C–C bond lengths center around 140 pm and show little variation.[7]
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Although phosphorine andpyridine are structurally similar, phosphorines are far less basic. The pKa of C5H5PH+ and C5H5NH+ 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 adative bond from phosphorus.[6]
Bothelectrophiles and strong, hardnucleophiles preferentially attack at phosphorus, but the ring aromaticity is sufficiently weak that the result is anaddition reaction, and not aromatic substitution.[6] Thus for examplemethyllithium adds to phosphorus in phosphorine whereas it adds to the 2-position of pyridine.[8] Halophosphorines do undergo noble-metal- orzirconocene-catalyzed substitution, and λ5-phosphorines exhibita much more traditional substitution chemistry.[6]
Unlikearsabenzene, phosphorine rarely participates inDiels-Alder-type cycloadditions; when it does, the coupling partner must be an extremely electron-poor alkyne. Phosphorinecomplexes are tolerable Diels-Alder reactants.[6]
Coordination complexes bearing phosphorine as aligand are known. Phosphorines can bind to metals through phosphorus center. Complexes of the diphospha analogue of2,2′-bipyridine are known. Phosphorines also form pi-complexes, illustrated by V(η6-C5H5P)2.[6]
