Metathesis degenerative

In the Phillips neohexene process147 2,4,4-trimethyl-2-pentene (8) is converted by cleavage with ethylene to neohexene (9) used in the production of a perfume musk. The starting material is commercial diisobutylene. Since it is a mixture of positional isomers (2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl-l-pentene) and the latter (7) participates in degenerative metathesis, effective utilization of the process requires the isomerization of 7 into 8. A bifunctional catalyst system consisting of an isomerization catalyst (MgO) and a heterogeneous metathesis catalyst is employed 131... 

Complex 4 can be regarded as titanium carbene Cp2Ti = CH2 coordinated by Me2AlCl. This is the first example of a well-defined metal carbene that catalyzes olefin metathesis and is re-isolated in high yield at the end of the reaction, Eq. (10). In a comparatively slow degenerative metathesis reaction (near equilibrium after 47 h at 51 °C). The 13C label of isobutylene was shown to grow into the methylene group of methylene cyclohexane [29]. 

Reaction Mechanism. It is generally accepted that the mechanism of the metathesis reaction involves a metallocarbene intermediate (Fig. 39). Decomposition of the intermediate proceeds to generate either the productive or degenerative product. Additional evidence for this type of reaction mechanism has been provided by the isolation of the reaction intermediates formed in homogeneous metathesis reactions. 

The cross metathesis between propane and methane to transform methane into higher alkanes has also been reported [35]. Mechanistic studies performed on a mixture of propane and C-labeled methane (1/1250) in a batch reactor afforded isotopomers of ethane (unlabeled, mono-, and dilabeled), confirming the incorporation of the labeled methane (>85%). Moreover, metathesis of the C-monolabeled ethane catalyzed by [TaH, /Si02] in a batch reactor was examined. The results revealed that the degenerative and productive alkane metathesis processes concomitantly occur the alkane product distribution afforded a 1/1 mixture of unlabeled and monolabeled methane [36]. Further... 

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