Methylenetriphenylphosphorane

Methylenetriphenylphosphorane
Names


IUPAC name Methylene(triphenyl)phosphorane
Identifiers
CAS Registry Number	3487-44-3
ChemSpider	121606
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
Jmol-3D images	Image
PubChem	137960
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 noted otherwise, data is 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 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 (1973). "Methylenecyclohexane". Org. Synth. ; Coll. Vol. 5, p. 751
↑ Bart, J. C. J. "Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane". Journal of the Chemical Society B: Physical Organic J. Chem. Soc. B 1969: 350–365. doi:10.1039/J29690000350.