Oligomerization, alkenes

Along with enabling technological advances in alkene polymerizations, the application of new ancillary ligands or cocatalysts has become significant in the field of alkene oligomerizations to obtain a-olefms. This research exploits a new phase in the development of known catalyst systems containing Gr, Ni, Pd, Ti metal centers, as well as Fe and Co as newcomers. 

The simplest possible alkene oligomerization reaction, the dimerization of ethylene to butenes, is a well-studied reaction, and an industrial process was also developed for the selective formation of 1-butene42 (IFP Alphabutol process). 

Cai, EX. Studies of a new alkene oligomerization catalyst derived from nickel sulfate. Catal. Today, 1999, 51, 153-160. 

At the highest CO pressures (and the lowest temperatures), the formation of multicarbonyl structures M +-(CO) is sometimes observed (Ni2+ and Cr2+) (506, 618-621). Ni2+/Si02 and Cr2+/Si02 are the only silica-supported catalysts active for alkene oligomerization at ambient temperature. 

The alkene elimination product usually dissociates readily but remains coordinated in some cases, as in a compound of the type (21-XXII).106 The /3-H elimination is the predominant termination step in catalytic alkene oligomerizations and polymerizations. 

A similar mechanism can also be written for alkene oligomerizations on Al centres in the idealized, transition form, because the Al d orbitals can hardly contribute to other bonds in the organoaluminium compounds... 

In conclusion, also in the case of alkene oligomerization/polymerization on metal-containing catalysts, the rate of surface reactions and hence, the concentrations of the surface species can be modified by tuning temperature and pressure... 

An analogous scheme can be advanced to rationalize the stereospecificity with which alkyl migration proceeds in metal alkyl-transition metal-catalyzed alkene oligomerization and polymerization reactions such as Ziegler-Natta polymerization and alkene metathesis. " ... 

A review is given of the use of spectroscopic techniques to investigate the MTG process. Examples are quoted of catalyst characterization, investigation of the first carbon-carbon bond formation, alkene oligomerization and catalyst deactivation through coke formation. 

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