Petasis reagent

• Bis ( η5 -2 ,4- cyclopentadiene -1-yl ) -dimethyl- titanium (IUPAC)
• Dimethyltitanocene

Orange to red solid

Fixed

• Slow decomposition with water
• Soluble in toluene

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In the Petasis reagent is the titanium complex dimethyltitanocene. It can be used analogously to the Tebbe reagent for olefination of ketones, aldehydes, esters, and lactones. Compared with the Tebbe reagent, it has the advantage of ease of manufacture and the higher stability. Furthermore, it also allows the introduction of larger residues, whereas with the Tebbe reagent only methylenation is possible.

Production

The production of the Petasis reagent can be easily accomplished from titanocene by substitution with methyl lithium or methyl magnesium chloride.

Reaction mechanism

The Petasis reagent is used analogously to the Tebbe reagent. The same Schrock carbene is probably formed as the active species. However, the reaction is carried out at a higher temperature (60-80 ° C). This is necessary to cleave methane from the titanium complex, thus forming a carbene.

The mixture obtained by methane releases Schrock carbene first adds to the carbonyl to form a Oxatitanacyclobutans. After ring opening yields the methylenierte product. Similarly to the case of the phosphorus in the Wittig reagent is the affinity of titanium to oxygen driving force of the reaction.

Use

Used the Petasis reagent for methylenate ketones, esters, aldehydes and lactones. Especially in carbonyl, which can not be obtained by Wittig olefination reaction (e.g., esters, lactones ), the Petasis reagent is an alternative. Unlike the Tebbe reagent can also be related in scope larger residues, such as a benzylidene introduce.