Related compounds | Formula C5H5P | |
Related -ines | ||
Phosphorine (IUPAC name: phosphinine) is a heavier 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.
Contents
Phosphorine is generally stable against air and moisture and can be handled without special air-free techniques. 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(CH2OH)3 and P(SiMe3)3).
The parent (unsubstituted) phosphorine was reported by Arthur J. Ashe III in 1971. Ring-opening approaches have been developed from phospholes.
Structure, bonding, and properties
Structural studies by electron diffraction reveal that phosphorine is a planar aromatic compound with 88% of the aromaticity of that of benzene. Potentially relevant to its high aromaticity are the well matched electronegativities of phosphorus (2.1) and carbon (2.5). The P-C bond length is 173 pm and the C-C bond lengths center around 140 pm and show little variation.
Although phosphorine and pyridine are structurally similar, phosphorines are far less basic. The pKa's of C5H5PH+ and C5H5NH+ are respectively -16.1 and 5.2. Methyl lithium adds to phosphorus in phosphorine whereas it adds to the 2-position of pyridine.
Phosphorine undergoes electrophilic substitution reactions like ordinary aromatic compounds: bromination, acylation, and so on.
Coordination chemistry
Coordination complexes bearing phosphorine as a ligand are known. Phosphorines can bind to metals through phosphorus center. Complexes of the diphospha analogue of bipyridine are known. Phosphorines also form pi-complexes, illustrated by V(η6-C5H5P)2.