Phosphole

Names

IUPAC name

1H-Phosphole

Identifiers

CAS Number

288-01-7^Y

3D model (Jmol)

InChI=1S/C4H5P/c1-2-4-5-3-1/h1-5H

SMILES

c1cccp1

Properties

Chemical formula

C₄H₅P

Molar mass

84.06 g·mol⁻¹

Related compounds

Pyrrole, bismole, arsole, stibole

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Infobox references

Phosphole is the organic compound with the chemical formula C₄H₄PH; 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 as ligands for transition metals and as precursors to more complex organophosphorus compounds.

Unlike the related 5-membered heterocycles pyrrole, thiophene, and furan, the aromaticity of phospholes is diminished, reflecting the reluctance of phosphorus to delocalize its lone pair. The main indication of this difference is the pyramidalization of phosphorus. The absence of aromaticity is also indicated by the reactivity of phospholes.

The parent phosphole was first described in 1983. It was prepared by low temperature protonation of lithium phospholide. Pentaphenylphosphole was reported in 1953. One route to phospholes is via the McCormack reaction, involving the addition of a 1,3-diene to a phosphonous chloride (RPCl₂) followed by dehydrohalogenation. Phenylphospholes can be prepared via zirconacyclopentadienes by reaction with PhPCl₂.

The behavior of the secondary phospholes, those with P-H bond, is dominated by the reactivity of this group. The parent phosphole readily rearranges by migration of H from P to carbon-2, followed by dimerization.

Most phospholes are tertiary, typically P-methyl or P-phenyl. The nonaromaticity of these phospholes is manifested in their reactivity but the P-C bonds remain intact. For example, they undergo Diels-Alder reactions with electrophilic alkynes. They are basic at P, serving as ligands.

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