Rhodium catalyzed cooligomerization of ethylene with conjugated dienes

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The catalytic cooligomerizations of olefins are among the most important C-C coupling reactions. Many transition metals have been used as catalysts for this kind of reactions. They are rhodium, ruthenium, nickel, cobalt, palladium and iron etc.. In this paper the rhodium catalyzed cooligomerizations of ethylene and conjugated dienes were mainly studied. Rhodium catalyzed cooligomerization of ethylene with dienes gives versatile products with wide industrial applications.
• For example, rhodium catalyzed cooligomerization of ethylene and 1,3-butadiene produces 1,4-hexadiene with a high selectivity to its trans-form, which is an important intermediate for the synthesis of EPDM (Ethylene-Propylene-Diene-Monomer).
• Rhodium catalyzed cooligomerization of ethylene with conjugated methyl linoleate yields the branched and unsaturated fatty substances. The linoleate is a fatty substance direct from nature and sustainable resources. The branched fatty products and their derivatives possess low melting points and pour points, which have attractive prospects of applications in lubricants, cosmetics and some other industrial fields.
• The rhodium catalyzed cooligomerization of ethylene and styrene affords 3-phenyl- 1-butene and serves as a model reaction for the synthesis of compounds with pharma- cological activity.
Newsolventsystemsweredevelopedforthesecatalyticreactions. Mixturesofpolyethy- leneglycol1000andwaterwereusedfortherhodiumcatalyzedcooligomerizationofethy- lene and 1,3-butadiene. By using PEG1000/water solvent systems selective synthesis of trans-1,4-hexadiene has been achieved under moderate reaction conditions. PEG1000 based novel temperature-dependent multi-solvent systems were developed for the reac- tion of ethylene and conjugated methyl linoleate. Some poly-ether modified phosphorous ligands were synthesized and used to condition the product selectivity and suppress the catalyst leaching. Cinnamyl chloride was used as catalyst promoter and was found to be very effective in reactivating the decayed rhodium catalysts. More interesting is that the addition of this organic chloride largely enhanced the activity of rhodium catalysts in the reaction of ethylene and styrene.