Petasis reagent

Petasis reagent
IUPAC name bis(η5-cyclopentadienyl)dimethyltitanium
Other names dimethyl titanocene
Identifiers
CAS number	1271-66-5
Jmol-3D images	Image 1
SMILES C[Ti](C)(C)c.c1cccc1.c2cccc2
Properties
Molecular formula	C12H16Ti
Molar mass	208.13 g/mol
Hazards
Main hazards	Irritant, incompatible with water and oxidizing agents
Y reagent (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

The Petasis reagent (not to be confused with the Petasis reaction) is dimethyl titanocene,^[1] Cp₂TiMe₂, readily prepared by the reaction of methylmagnesium chloride^[2] or methyllithium^[3] with titanocene dichloride:

Cp₂TiCl₂ + 2 "Me⁻" → Cp₂TiMe₂ + 2 Cl⁻

It is used for transforming carbonyl groups to terminal alkenes, much like the Tebbe reagent or Wittig reaction. Unlike the Wittig reaction, the Petasis reagent can react with a wide range of carbonyls, including aldehydes, ketones and esters.^[4] The Petasis reagent is also more air stable than the Tebbe reagent, and can be isolated as a pure solid, or used directly as a solution in toluene-THF.

The active olefinating reagent, Cp₂TiCH₂, is prepared by heating the Petasis reagent in toluene or THF to 60 °C.

The reaction mechanism is very similar to that of the Tebbe reagent, first yielding a titanium carbene which forms a four membered oxatitanacyclobutane and than releases the terminal alkene.^[5]

References

1. ^ N. A. Petasis and E. I. Bzowej (1990). "Titanium-mediated carbonyl olefinations. 1. Methylenations of carbonyl compounds with dimethyltitanocene". J. Am. Chem. Soc. 112 (17): 6392–6394. doi:10.1021/ja00173a035. 
2. ^ Payack, J. F.; Hughes, D. L.; Cai, D.; Cottrell, I. F.; Verhoeven, T. R. (2002), "Dimethyltitanocene", Org. Synth. 79: 19, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=v79p0019 
3. ^ Claus, K.; Bestian, H. (1962). "Über die Einwirkung von Wasserstoff auf einige metallorganische Verbindungen und Komplexe". Justus Liebigs Ann. Chem. 654: 8. doi:10.1002/jlac.19626540103. 
4. ^ Hartley, R. C.; Li, J.; Main, C. A.; McKiernan, G. J. (2007). "Titanium carbenoid reagents for converting carbonyl groups into alkenes". Tetrahedron 63: 4825–4864. doi:10.1016/j.tet.2007.03.015. 
5. ^ Meurer, Eduardo Cesar; Santos, Leonardo Silva; Pilli, Ronaldo Aloise; Eberlin, Marcos N. (2003). "Probing the Mechanism of the Petasis Olefination Reaction by Atmospheric Pressure Chemical Ionization Mass and Tandem Mass Spectrometry". Organic Letters 5: 1391. doi:10.1021/ol027439b.