Tebbe's reagent

  • μ - Chlorobis (cyclopentadienyl ) - ( dimethylaluminium ) - μ -methyl titanium (IUPAC)

Red solid

Fixed

0.93 g · cm -3

  • Soluble in toluene, benzene, and dichloromethane
  • Almost insoluble in saturated hydrocarbons

636 mg · kg -1 ( LD50, rat, oral)

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The Tebbe reagent ( to Frederick Nye Tebbe, Fred Tebbe short ) is an organometallic compound which is used for methylenation of ketones or esters, the Tebbe methylenation. It is a bridged dinuclear complex with a titanium or an aluminum core. The titanium core which is bridged by a methyl group and a chlorine bond with the aluminum core, two cyclopentadienyl radicals are attached. On aluminum core are still two methyl radicals. The Tebbe reagent is a pyrophoric red solid and is therefore handled under protective gas. Commercially, it is usually as a solution ( for example: in toluene) available.

Production

Tebbe reagent is prepared from titanocene dichloride ( Cp2Cl2Ti ) and trimethylaluminum by three days of stirring at room temperature. The actually required for methylenation Schrock carbene thereof may be mild bases (eg, pyridine) obtained in situ by treatment.

Reaction mechanism

The mixture obtained by addition of a base Schrock carbene first adds to the carbonyl to form a Oxatitanacyclobutans. After ring opening yields the methylenierte product.

Similarly as in the case of phosphorus in the Wittig reagent is the affinity of titanium to oxygen driving force of the reaction.

Range of applications

Unlike other olefination (see, Wittig reaction, Horner-Wadsworth -Emmons reaction ), the use of the Tebbe reagent is limited to the introduction of methyl groups. However, in use of the Tebbe reagent esters can also be used, which can not be implemented for example by the Wittig reaction.

Another field of application of the Tebbe reagent lies in the synthesis of titanium enolates. The derived from a carboxylic acid chloride and the Tebbe reagent Oxatitanacyclobutan derivative decomposes with elimination of chloride ion to the titanium enolate.

Alternatives to the Tebbe reagent are the Petasis reagent and the Lombardo reagent.

CAS registry number Methylenes Pyrophoricity Shielding gas Trimethylaluminium Addition reaction Cyclobutane Horner–Wadsworth–Emmons reaction Enolate anion
763727
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