Methylenetriphenylphosphorane

Methylenetriphenylphosphorane
Names
	IUPAC name Methylene(triphenyl)phosphorane
Identifiers
CAS Number	3487-44-3;
3D model (JSmol)	Interactive image;
ChemSpider	121606;
PubChem CID	137960;
CompTox Dashboard (EPA)	DTXSID20188410 ;
	InChI InChI=1S/C19H17P/c1-20(17-11-5-2-6-12-17,18-13-7-3-8-14-18)19-15-9-4-10-16-19/h2-16H,1H2 Key: XYDYWTJEGDZLTH-UHFFFAOYSA-N; InChI=1/C19H17P/c1-20(17-11-5-2-6-12-17,18-13-7-3-8-14-18)19-15-9-4-10-16-19/h2-16H,1H2 Key: XYDYWTJEGDZLTH-UHFFFAOYAU;
	SMILES C=P(C1=CC=CC=C1)(C2=CC=CC=C2)C3=CC=CC=C3;
Properties
Chemical formula	C19H17P
Appearance	yellow solid
Density	1.19 g/cm3
Solubility in water	decompose
Solubility	THF
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Methylenetriphenylphosphorane is an organophosphorus compound with the formula Ph₃PCH₂. It is the parent member of the phosphorus ylides, popularly known as Wittig reagents. It is a highly polar, highly basic species.

Preparation and use

Methylenetriphenylphosphorane is prepared from triphenylphosphine and methyl bromide followed by deprotonation of the resulting phosphonium salt using a strong base like butyllithium:^[1]

Ph₃PCH₃Br + BuLi → Ph₃PCH₂ + LiBr + BuH

The compound is generally not isolated, instead it is used in situ.

Methylenetriphenylphosphorane is used to replace oxygen centres in aldehydes and ketones with a methylene group:

R₂CO + Ph₃PCH₂ → R₂C=CH₂ + Ph₃PO

The phosphorus-containing product is triphenylphosphine oxide.

Structure

Crystallographic characterization of the colourless ylide reveals that the phosphorus atom is approximately tetrahedral. The PCH₂ centre is planar and the P=CH₂ distance is 1.661 Å, which is much shorter than the P-Ph distances (1.823 Å).^[2] The compound is usually described as a combination of two resonance structures:

Ph₃P⁺CH₂⁻ ↔ Ph₃P=CH₂

References

^ Georg Wittig U. Schoellkopf (1960). "Methylenecyclohexane". Organic Syntheses. 40: 66. doi:10.15227/orgsyn.040.0066; Collected Volumes, vol. 5, 1973, p. 751.
^ Bart, J. C. J. "Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane". Journal of the Chemical Society B. 1969: 350–365. doi:10.1039/J29690000350.

[1] Georg Wittig U. Schoellkopf (1960). "Methylenecyclohexane". Organic Syntheses. 40: 66. doi:10.15227/orgsyn.040.0066; Collected Volumes, vol. 5, 1973, p. 751.

[2] Bart, J. C. J. "Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane". Journal of the Chemical Society B. 1969: 350–365. doi:10.1039/J29690000350.

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