Relationship between the Stereospecificity
of Lanthanide Catalysts and the Structures
of Active Sites and Dienes, the Nature
of a Cocatalyst, and Preparation Conditions

Yu. B. Monakov, Z. M. Sabirov, V. N. Urazbaev, and V. P. Efimov

Institute of Organic Chemistry, Ufa Research Center, Russian Academy of Sciences, Ufa, 450054 Bashkortostan, Russia

Received September 18, 2000

Abstract—Several types of active sites can be formed during the polymerization of dienes in the presence of
lanthanide catalytic systems. These sites differ in the nearest environment of a lanthanide atom (the numbers of
chlorine and carbon atoms) and in the number of lanthanide–carbon bonds involved in chain growth. Quantum-
chemical calculation shows that the -allyl binding of the terminal unit of a growing polymeric chain with the
lanthanide atom of an active site may be the reason for the cis-stereospecificity of the site. Therefore, the active
sites containing electron-acceptor chlorine atoms that favor -allyl binding can form cis-polydienes. Depending
on the conditions of catalytic system preparation, primarily on the nature of an organic compound of a nontran-
sition metal, one or another set of active sites is formed that can affect its stereospecificity. The quantitative
analysis of kinetic data for diene polymerization shows that the anti-syn isomerization of terminal units of
growing polymeric chains made a certain contribution to the formation of trans-1,4 units in the presence of cis-
regulating active sites.

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