Olefin exchange

Olefin exchange reactions, 431 Olefin Metathesis and Metathesis... 

Application of Transition State Theory to Traditional and Cavitating Ultrasound Olefin Exchange... 

In the context of the accepted olefin isomerization mechanism, our results illustrate that fra/rsition-state theory can accurately model the competition between C-H and C-D activation for olefin exchange (isomerization) for the case of... 

Olefin exchange has been used for the preparation of certain plati-num(II) complexes (67). Thus, trimethylvinylsilane replaces ethylene in Zeise s salt to give the compound K[Cl3Pt(H2C=CHSiMe3)]. The SiMe3 group in this complex is readily cleaved by water (wet acetone) with elimination of hexamethyldisiloxane and regeneration of Zeise s salt, but resists attack by pyridine N-oxide, which instead replaces a chlorine atom (67). 

In some early attempts, the formation of i73-allylic complexes containing organosilicon groups was not successful. Thus, the reaction of allyltrimethylsilane with Zeise s salt occurred with olefin exchange to give an -complex, K[Cl3Pt(H2C=CH—CH2SiMe3)] (5i). 

The processes of olefin exchange, double bond migration and cis—trans isomerisation, observed to occur concomitant with hydrogenation, may be accounted for by considering that the formation of the half-hydrogenated state is reversible. For olefin exchange we can write... 

For olefins possessing one or more a-CH2 groups, it is possible that olefin exchange and isomerisation could occur through the formation of an adsorbed 7r-allylie intermediate [87]. The appropriate mechanism for olefin exchange and double bond migration is... 

Comparison of these results with those presented for ethylene in Table 7 show that, for each catalyst, the two reactions show close similarities suggesting that the general features of the mechanisms are the same for both reactions. There are some important differences in detail between the two reactions, particularly with palladium and iridium. With palladium, olefin exchange occurs more readily with propene than with ethylene. This may be due to easier desorption of propene or possibly due to an alternative mechanism such as... 

Whilst the use of deuterium allows a deeper insight into the mechanism of catalytic reactions than was previously possible, it nevertheless does not allow an absolutely rigorous analysis to be made. One of the major problems in ethylene—deuterium and propene—deuterium studies is that there is no method whereby the true fraction of olefin which has undergone an olefin—alkyl—olefin cycle and reappeared in the gas phase as olefin-d0 can be determined. This is especially true for reactions on metals such as palladium, ruthenium and rhodium where the olefin exchange results sug-... 

Fig. 18. The effect of mercury coverage ( Hg) upon the rates of hydrogenation (O), olefin exchange ( ) and isomerisation ( ) of but-l-ene over rhodium—silica at 48°C [129].

It has been speculated (5) that the olefin metathesis reaction mech-nism involves a four-centered quasi-cyclobutane transition state. The three basic steps postulated for the reaction, namely, formation of a bis-olefin-tungsten complex, transalkylidenation and olefin exchange, may account, in general, for the initiation and propagation steps in the ringopening polymerization of cycloolefins. Several modes of termination have been considered, but suitable data to test these are not yet available. 

N. Calderon, H. Y. Chen, and K. W. Scott, Tetrahedron Lett., 1967, 3327. Calderon was the first to coin the term olefin metathesis for the olefin exchange reaction that is typified by the Triolefin Process. 

Irradiation of Fe(CO) (olefin) complexes leads to olefin exchange . When the olefins bear halogen substituents, the transformation ... 

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