Alkene metathesis thermodynamic stability

The term alkene (olefin) metathesis refers to the equilibrium reaction shown in equation (1) in which the alkylidene groups of a pair of alkenes are exchanged with one another in the presence of a transition metal-containing catalyst. The reaction involves the net cleavage of the bonds of the substrate(s) and formation of the new carbon-carbon double bonds of the prodncts. Once equilibrium has been established, the resultant prodnct mixture has a distribution of alkenes (including isomers) that is determined solely by the relative thermodynamic stabilities of the prodncts. 

The mechanism of olefin metathesis was originally worked out in the early 1970s by H risson and Chauvin. The mechanism involves the nonpairwise cleavage of C=C bonds that occurs in a [2-I-2] cycloaddition reaction between a carbene and an alkene to form an intermediate metallacyclobutane, as shown in Figure 19.23. The metallo-cyclobutane can open in either direction, such that an equilibrium mixture of alkenes results with the product distribution dictated by the thermodynamic stabilities of the different alkenes. Two of the more important organometallic catalysts for olefin metathesis are shown in Figure 19.24. 

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