Petasis reagent

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Structural formula
Structural formula of the Petasis reagent
General
Surname Petasis reagent
other names
  • Bis (η 5 -2,4-cyclopentadien-1-yl) dimethyltitanium ( IUPAC )
  • Dimethyl titanocene
Molecular formula C 12 H 16 Ti
Brief description

orange to red solid

External identifiers / databases
CAS number 1271-66-5
EC number 679-889-8
ECHA InfoCard 100.204.841
Wikidata Q417078
properties
Molar mass 208.13 g mol −1
Physical state

firmly

solubility
  • slow decomposition with water
  • soluble in toluene
safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

The Petasis reagent is the titanium complex dimethyl titanocene . It can be used analogously to the Tebbe reagent for the olefination of ketones , aldehydes , esters and lactones . Compared to the Tebbe reagent, it has the advantage of easier production and greater stability. Furthermore, it also allows the introduction of larger residues, while only methenylation is possible with the Tebbe reagent.

The reagent is named after the Cypriot-US chemist Nicos A. Petasis (* 1954).

Manufacturing

The preparation of the Petasis reagent can easily be accomplished from titanocene dichloride by substitution with methyl lithium or methyl magnesium chloride . In the following, the abbreviation Cp is used as an abbreviation for the cyclopentadienyl ligands of the complex compounds that occur .

Synthesis of the Petasis reagent

Reaction mechanism

The Petasis reagent is used in the same way as the Tebbe reagent. The same Schrock carbene is probably also formed as the active species . However, the reaction is carried out at a higher temperature (60-80 ° C). This is necessary in order to split off methane from the titanium complex and thus form a carbene complex.

Formation of the Petasis carbene

The methylenation proceeds analogously to the reaction with the Tebbe reagent : The Schrock carbene obtained by splitting off methane first adds to the carbonyl component to form an Oxatitana cyclobutane . After ring opening, the methylenated product is obtained. As in the case of phosphorus in the Wittig reaction , the affinity of titanium for oxygen is the driving force behind the reaction.

Use of the Petasis reagent

use

The Petasis reagent is used for the methylenation of ketones, esters, aldehydes and lactones. The Petasis reagent offers an alternative, especially for carbonyl functions that cannot be olefined by the Wittig reaction (e.g. esters, lactones). In contrast to the Tebbe reagent, larger residues, such as a benzylidene residue, can also be introduced to a limited extent.

Individual evidence

  1. ↑ a b c Data sheet for Petasis reagent from Acros, accessed February 26, 2010.
  2. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  3. ↑ Tanja Schirmeister; Carsten jewelry; Peter Richard Wich: Beyer / Walter Organic Chemistry . 25th, completely revised edition. Hirzel, Stuttgart 2016, ISBN 978-3-7776-1673-5 , pp. 700-701 .
  4. ↑ a b Jie Jack Li: Name reactions: A collection of detailed mechanisms and synthetic applications . 5th ed.Springer, Cham 2014, ISBN 978-3-319-03979-4 , pp. 474-475 , doi : 10.1007 / 978-3-319-03979-4 .

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