Petasis reagent
Structural formula of the Petasis reagent
Ball-and-stick model of the Petasis reagent
Names
IUPAC name
Bis(η5-cyclopentadienyl)dimethyltitanium
Other names
Dimethyltitanocene
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.204.841
EC Number
  • 679-889-8
  • InChI=1S/2C5H5.2CH3.Ti/c2*1-2-4-5-3-1;;;/h2*1-5H;2*1H3;/q2*-1;;;+2 ☒N
    Key: AFEQRLILWYRIDQ-UHFFFAOYSA-N ☒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
  • [Ti](C)(C).c1[cH-]ccc1.c2[cH-]ccc2
Properties
C12H16Ti
Molar mass 208.13 g/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Irritant, incompatible with water and oxidizing agents
GHS labelling:
GHS02: FlammableGHS07: Exclamation markGHS08: Health hazard
Danger
H225, H304, H315, H319, H332, H360, H370, H372
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, named after Nicos A. Petasis, is an organotitanium compound with the formula Cp2Ti(CH3)2.[1] It is an orange-colored solid.

Preparation and use

The Petasis reagent is prepared by the salt metathesis reaction of methylmagnesium chloride or methyllithium[2] with titanocene dichloride:[3]

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

This compound is used for the transformation of carbonyl groups to terminal alkenes. It exhibits similar reactivity to the Tebbe reagent and Wittig reaction. Unlike the Wittig reaction, the Petasis reagent can react with a wide range of aldehydes, ketones and esters.[4] The Petasis reagent is also very air stable, and is commonly used in solution with toluene or THF.

The Tebbe reagent and the Petasis reagent share a similar reaction mechanism. The active olefinating reagent, Cp2TiCH2, is generated in situ upon heating. With the organic carbonyl, this titanium carbene forms a four membered oxatitanacyclobutane that releases the terminal alkene.[5]

Formation of the active olefinating reagent
Reaction of the active olefinating reagent with a carbonyl compound

In contrast to the Tebbe reagent, homologs of the Petasis reagent are relatively easy to prepare by using the corresponding alkyllithium instead of methyllithium, allowing the conversion of carbonyl groups to alkylidenes.[6]

See also

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: 8–19. doi:10.1002/jlac.19626540103.
  3. ↑ Payack, J. F.; Hughes, D. L.; Cai, D.; Cottrell, I. F.; Verhoeven, T. R. (2002). "Dimethyltitanocene". Organic Syntheses. 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.
  6. ↑ Petasis, Nicos A.; Morshed, M. Monzur; Ahmad, M. Syarhabil; Hossain, M. Mahmun; Trippier, Paul C. (2012-03-15), "Bis(cyclopentadienyl)dimethyltitanium", in John Wiley & Sons, Ltd. (ed.), Encyclopedia of Reagents for Organic Synthesis, Chichester, UK: John Wiley & Sons, Ltd., pp. rb126.pub3, doi:10.1002/047084289x.rb126.pub3, ISBN 978-0-471-93623-7
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