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 phosphinocarbenes. 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).
The cyaphide ion P≡C− as the phosphorus cyanide cousin is not known as a salt and only observed in the gas phase. In silico measurements reveal that the -1 charge in this ion is location mainly on carbon (0.65). On the other hand the molecule does exist as a terminal ligand in a certain ruthenium transition metal complex trans-[(dppe)2Ru(H)(C≡P)] stabilized by dppe.
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