Acyclic olefins, disproportionation

The alkene metathesis reaction arose serendipitously from the exploration of transition-metal-catalysed alkene polymerisation. Due to the complexity of the polymeric products, the metathetic nature of the reaction seems to have been overlooked in early reports. However, in 1964, Banks and Bailey reported on what was described as the olefin disproportionation of acyclic alkenes where exchange was evident due to the monomeric nature of the products [8]. The reaction was actually a combination of isomerisation and metathesis, leading to complex mixtures, but by 1966 Calderon and co-workers had reported on the preparation of a homogeneous W/Al-based catalyst system that effected extraordinarily rapid alkylidene... 

Table 9. Disproportionation of cyclic-acyclic olefins 58 Type IV reactions C + A < -t s...

Independently from the results of ring-opening polymerization, Banks and Bailey [16] reported a disproportionation reaction of acyclic olefins, the formation of ethylene and 2-butene from propylene Eq. (2). 

In the course of time it appeared that many olefinic substrates could undergo this reaction in the presence of a transition metal compound, such as substituted alkenes, dienes, polyenes, and cyclic alkenes, and even alkynes. Calderon et al. were the first to realize that the ring-opening polymerization of cycloalkenes, which they observed with their tungsten-based catalyst system [4], and the disproportionation of acyclic olefins are, in fact, the same type of reaction. They introduced the more general name metathesis [2], The metathesis reaction has now become a common tool for the conversion of unsaturated compounds. In view of the limited space this intriguing reaction is reviewed only briefly more information can be found in a detailed and extensive monograph [5]. 

At this time ring-opening metathesis polymerization and metathesis of acyclic olefins -originally considered as olefin disproportionation [7] - were regarded as two different reaetions. Calderon recognized in 1972 that these both are two sides of the same coin and introduced the term olefin metathesis for this reaction type [8-11]. 

Disproportionation reactions of acyclic mono-olefins can be classified into three types (I) reactant is a single olefin, (II) reactants are double-bond isomers, and (III) reactants are different olefins. Generalized equations and examples are ... 

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