Metallocene Complexes of Group 4 Elements in the Polymerization of Monoolefins

Abstract

Metallocene compounds are becoming an important class of catalyst for the synthesis of organic molecules and polymers [1–6]. These complexes also have good potential to act as catalysts or catalyst precursors for a number of organic reactions [2]. The discovery of Group 4 metallocene-alumoxane systems [7–10] as catalysts for polymerization reactions has opened up a new frontier in the area of organometallic chemistry and polymer synthesis [11–18]. Metallocene systems are comprised of 1) bicomponents consisting of a metallocene and an alumoxane and 2) a single component such as [Cp2MR]⁺[B(C₆F₅)₄]⁻. The polymerization of monoolefins by metallocenes in comparison to conventional Ziegler-Natta systems [19–25] offers a versatile possibility to polymer synthesis [26]. The broader flexibility of electronic and steric variations in the cyclopentadienyl (Cp) type ligands allows greater maneuvering in the design of catalyst systems. Such modifications govern the polyinsertion reaction leading to regio- and stereoregular polyolefins. Scientific undestandings in this area have reached a level where full commercial realization is a possibility. Despite all the developmental efforts in the area of metallocene-catalyzed polymerization reactions, no comprehensive review is available on this topic. The scope of this review is restricted to monoolefin polymerizations catalyzed by Group 4 metallocene complexes.