Metathesis of olefins

Olefin metathesis is the disproportionation of two olefin molecules, via cleavage of the double bonds as shown in the equation  

The reaction was announced by Phillips Petroleum in 1964 and became known as the Triolefm process because it was first used to balance the production of olefins from naphtha steam crackers by converting propylene into ethylene and butene-2.  

As the scope of the reaction increased, the name Olefin Metathesis was introduced by Goodyear, who also pioneered the use of homogeneous catalysts. The reaction had first been recognized during experiments on the development of a heterogeneous catalyst to replace mineral acids in alkylation reactions. Molybdenum hexacarbonyl catalyst supported on alumina produced 2-pentene (40%) from mixed n-butenes together with propylene (51%) and hexene (9%). Tungsten hexacarbonyl was less active than the molybdenum catalyst, and in total contrast, it was found that chromium hexacarbonyl acted as a polymerization catalyst. 

BP has developed an even more active rhenium oxide catalyst supported on alumina that operates at 20°-50°C, with an equilibrium conversion higher than 60%. This follows from an observation by Philhps that alumina is a more suitable support than silica. 

---

Exchange of alkylidene groups of alkenes—metathesis of olefins... 

Recently, additional catalyst systems which are effective for the metathesis of olefins bearing polar functional groups have been revealed. Nakamura and co-workers found that either WC16 or (C2H50)2MoCl3 in combination with triethylborane were capable of converting c/s-9-octa-decenyl acetate to 1,18-diacetoxy-9-octadecene and 9-octadecene at the rather high temperature of 178°C (89). 

In summary, the metathesis of olefins substituted with polar functional... 

In catalyst preparation, one can use this knowledge to determine the relative contributions of various hydroxyl groups before and after application of the active phase onto the support. In this way Sibeijn etal. [31] established that rhenium oxide attached to acidic sites of the alumina support exhibits higher activity for the metathesis of olefins than rhenium oxide on neutral or basic sites. As, however, rhenium species preferentially exchange with basic hydroxyls, one needs to increase the loading above a certain value (6 wt% for an alumina of 200 m2/gram) before the catalyst exhibits appreciable activity [31]. 

This is a major achievement, mainly due to Basset and his group, in surface organometallic chemistry because it has been thus possible to prepare single site catalysts for various known or new catalytic reactions [53] such as metathesis of olefins [54], polymerization of olefins [55], alkane metathesis [56], coupHng of methane to ethane and hydrogen [57], cleavage of alkanes by methane [58], hydrogenolysis of polyolefins [59] and alkanes [60], direct transformation of ethylene into propylene [61], etc. These topics are considered in detail in subsequent chapters. 

Fig. 4 Incremental yields for addition of Lewis acids to chloroaluminate ILs. Metathesis of olefins...

The reaction is called metathesis of olefins.557 In the example shown above, 2-pentene (either cis, trans, or a cis-trans mixture) is converted to a mixture of about 50% 2-pentene, 25% 2-butene, and 25% 3-hexene. The reaction is an equilibrium and the same mixture can be obtained by starting with equimolar quantities of 2-butene and 3-hexene.558 In general, the... 

---