Name: alkene metathesis mechanism: scission and reformation of c=c bonds
Uploaded: 2023-01-10T17:30:47
Description: Alkene or olefin metathesis reaction, catalyzed by organometallic complexes, involves the redistribution of groups at each end of the C=C double bond to ...

Alkene metathesis occurs in two stages: Intermediate formation and catalytic cycle. Each stage comprises two steps: ring-forming [2 + 2] cycloaddition and ring-opening fragmentation.
In the first stage, the reaction is initiated by the [2 + 2] addition of the starting alkene to the metallocarbene complex.
There are two possible cycloadditions, each resulting in an unstable four-membered metallacycle complex.
The complexes undergo fragmentation to form corresponding metal alkylidene intermediates, each containing the resp...

alkene metathesis mechanism: scission and reformation of c=c bonds

Alkene or olefin metathesis reaction, catalyzed by organometallic complexes, involves the redistribution of groups at each end of the C=C double bond to produce new alkene molecules. The reaction mechanism involves two stages, that are intermediate formation and catalytic cycle. Each stage consists of two key steps namely ring-forming [2 + 2] cycloaddition and ring-opening fragmentation.
The first stage involves the initiation of the reaction by [2 + 2] cycloaddition of the starting alkene to the metallocarbene complex. There are two possibilities of cycloaddition reaction. Each results in the formation of an unstable four-membered metallacycle complex.
<img alt="Figure1" src="/files/ftp_upload/12319/12319_PT_Figure_1.svg" style="text-align: center; height: 90px;" />&#160;

<img alt="Figure2" src="/files/ftp_upload/12319/12319_PT_Figure_2.svg" style="height: 90px;" />
The fragmentation of each complex gives a metal alkylidene intermediate each with the corresponding parts of the starting alkene. These intermediates serve as the catalyst for the second stage of the mechanism.
<img alt="Figure3" src="/files/ftp_upload/12319/12319_PT_Figure_3.svg" style="text-align: center; height: 180px;" />&#160; &#160; &#160; &#160; &#160; &#160; &#160; &#160;<img alt="Figure4" src="/files/ftp_upload/12319/12319_PT_Figure_4.svg" style="height: 180px;" />
In the catalytic cycle, each metal alkylidene intermediate reacts parallely with the starting alkene via ring-forming cycloaddition and rin-opening fragmentation. The reactions generate a new recombined alkene, and an ethylene molecule with simultaneous regeneration of metal alkylidene for the next catalytic cycle.
<img alt="Figure5" src="/files/ftp_upload/12319/12319_PT_Figure_5.svg" style="text-align: center; height: 225px;" />

Alkene Metathesis Mechanism: Scission and Reformation of C=C Bonds

Alkene or olefin metathesis reaction, catalyzed by organometallic complexes, involves the redistribution of groups at each end of the C=C double bond to ...