Phosphaalkyne

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A new batch of phosphaalkynes

In chemistry, phosphaalkynes (IUPAC name: alkylidynephosphanes) are organophosphorus compounds that have a phosphorus-carbon triple bond.[1]

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.[1] 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).

Cyaphide ion

The first unequivocal example of a transition metal cyaphide complex

The cyaphide ion[1] 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). The synthesis of organometallic complexes featuring this elusive moiety can be achieved using two different synthetic routes:

1. Using SiR3 Functionalised Phosphaalkynes

The moiety does exist as a terminal ligand in the ruthenium transition metal complex trans-[(dppe)2Ru(H)(C≡P)], which is stabilized by dppe.[2] Recently, the synthesis and electronic structure of the first cyaphide-alkynyl complexes has been reported.[3] The novel complexes trans-[Ru(dppe)2(C≡CR)(C≡P)] (R = CO2Me, C6H4OMe) are the first complexes to incorporate cyaphide as part of a conjugated system.

2. Using the 2-phosphaethynolate anion (OC≡P)

Recently, the synthesis of the first actinide cyaphide complex has been reported, formed through C-O bond cleavage of the phosphaethynolate anion.[4] Reaction of the uranium complex [((Ad,MeArO)3N)UIII(DME)] with [Na(OCP)(dioxane)2.5] in the presence of 2.2.2-cryptand results in the formation of a dinuclear, oxo-bridged uranium complex featuring a pendant C≡P fragment.

References

  1. ^ a b c "Cyaphide (C≡P): The Phosphorus Analogue of Cyanide (C≡N)" Robert J. Angelici Angew. Chem. Int. Ed. 2007, 46, 330 – 332 doi:10.1002/anie.200603724
  2. ^ "Making the True "CP" Ligand." Cordaro et al. Angew. Chem. Int. Ed. 2006, 45, 6159 - 6162 doi:10.1002/anie.200602499
  3. ^ "Synthesis and electronic structure of the first cyaphide-alkynyl complexes." Trathen et al. Dalton Trans. 2014, 43, 9004 - 9007 doi:10.1039/C4DT01108B
  4. ^ "Formation of a Uranium-Bound η1-Cyaphide Ligand via Activation and C-O Bond Cleavage of Phosphaethynolate." Hoerger et al., Organometallics, 2017, in press doi:10.1021/acs.organomet.7b00590
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