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In chemistry, phosphaalkynes ( IUPAC name: alkylidynephosphanes) are organophosphorus compounds that have a phosphorus- carbon triple bond.

Two types of phosphaalkynes are recognized. One type of phosphaalkyne is a heavier analogue of nitriles (R-C≡N), i.e. P replaces N in a nitrile. Another type of phosphaalkyne feature pentavalent, three coordinate phosphorus. Such species can also be described as ylides or phosphino carbenes. The phosphorus version of the isonitriles R-P≡C, which would be called isophosphaalkynes, has not been observed.

In 1950, H. Albers reported the first indication of the existence of the parent compound of phosphaalkynes (type A), H-C≡P. This compound was identified by infrared absorption spectrometry, and its synthesis was improved by Manfred Regitz in 1987. The synthesis of the first kinetically stable phosphaalkyne, which has a tert-butyl group as a substituent R ( tert-Butylphosphaacetylene), was reported in 1981 by Gerd Becker and Werner Uhl. These phosphaalkynes undergo 1,2- addition reactions and cycloadditions .

In 2000, Guy Bertrand reported the first structure of the type B phosphaalkyne. Its P-C-R bond angle is 152.6 degrees, so this type of phosphaalkyne may be best described by a phosphorus vinyl ylide structure (B2).