Petasis reagent

Petasis reagent

Names
IUPAC name Bis(η^5-cyclopentadienyl)dimethyltitanium
Other names Dimethyltitanocene
Identifiers
CAS Number	1271-66-5
3D model (Jmol)	Interactive image
ChemSpider	34981143
ECHA InfoCard	100.204.841
InChI InChI=1S/2C5H5.2CH3.Ti/c2*1-2-4-5-3-1;;;/h2*1-5H;2*1H3;/q2*-1;;;+2 Key: AFEQRLILWYRIDQ-UHFFFAOYSA-N InChI=1/2C5H5.2CH3.Ti/c2*1-2-4-5-3-1;;;/h2*1-5H;2*1H3;/q2*-1;;;+2/r2C5H5.C2H6Ti/c2*1-2-4-5-3-1;1-3-2/h2*1-5H;1-2H3/q2*-1;+2 Key: AFEQRLILWYRIDQ-MEMJIDHRAL
SMILES C[Ti](C)(C)c.c1cccc1.c2cccc2
Properties
Chemical formula	C12H16Ti
Molar mass	208.13 g/mol
Hazards
Main hazards	Irritant, incompatible with water and oxidizing agents
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

The Petasis reagent is an organotitanium compound with the formula Cp₂Ti(CH₃)₂.^[1] It is an orange-colored solid.

Preparation and use

It prepared by the salt metathesis reaction of methylmagnesium chloride or methyllithium^[2] with titanocene dichloride:^[3]

Cp₂TiCl₂ + 2 CH₃MgCl → Cp₂Ti(CH₃)₂ + 2 MgCl₂

The compound is used for transforming carbonyl groups to terminal alkenes. In terms of reactivity, it resembles the Tebbe reagent and 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 is commonly used directly as a solution in toluene THF.

The reaction mechanism is very similar to that of the Tebbe reagent. The active olefinating reagent, Cp₂TiCH₂, is generated in situ upon heating the solution of Petasis reagent in toluene or THF to 60 °C. With the organic carbonyl, this titanium carbene forms a four membered oxatitanacyclobutane that releases the terminal alkene.^[5]

See also

• Nysted reagent
• Titanium-Zinc Methylenation

References

1. N. A. Petasis & 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. 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.
3. Payack, J. F.; Hughes, D. L.; Cai, D.; Cottrell, I. F.; Verhoeven, T. R. (2002). "Dimethyltitanocene". Org. Synth. 79: 19.
4. Hartley, R. C.; Li, J.; Main, C. A.; McKiernan, G. J. (2007). "Titanium carbenoid reagents for converting carbonyl groups into alkenes". Tetrahedron. 63 (23): 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 (9): 1391–4. doi:10.1021/ol027439b. PMID 12713281.