Metallocenes synthetic approaches

Synthetic Approaches Toward 2-Alkyl-4-Aryl-Substituted ansa Metallocenes... 

Synthetic Approach Toward 4,7-Alkyl-Substituted Metallocenes... 

The chemistry of //// //-metallocene compounds has been the subject of several reviews. Structural aspects affecting the catalytic activity and the application of these complexes as catalysts for the homo- and co-polymerization of olefins have been considered.323 The evolution of the //// //-bridge complexes in terms of the various synthetic approaches used to construct the bridged ligand framework, the variety of bridges introduced, and the effect of the bridge on the structure and reactivity of ////.y//-titanocene and other transition metal complexes as compared with their unbridged counterparts has been reviewed.1634... 

The versatility of polymerization resides not only in the different types of polymerization reactions and types of reactants that can be polymerized, but also in variations allowed by step-growth synthesis, copolymerization, and stereospecific polymerization. Chain polymerization is the most important kind of copolymerization process and is considered separately in Chapter 7, while Chapter 9 describes the stereochemistry of polymerization with emphasis on the synthesis of polymers with stereoregular structures by the appropriate choice of polymerization conditions, including the more recent metallocene-based Ziegler-Natta systems. Synthetic approaches to starburst and hyperbranched polymers which promise to open up new applications in the future are considered in an earlier chapter dealing with step-growth polymerization. 

INTRODUCTION New types of linear low-density polyethylenes (LLDPE) based on the metallocene catalyst technology have been introduced recently in the market place. Metallocene-based Ziegler-Natta catalysts utilize a new synthetic approach for the polymerization of poly(a-olefins).( 5) Metallocene precatalysts are based primarily on group IV transition metals (primarily titcuiium and zirconium straddled by a pair of cyclic alkyl molecules) and require a coactivator, which is typically methylalumoxane but certain acids containing noncoordinating anions as bases also work well. 

The preparation of most monosubstituted and many polysubstituted metallocenes (especially ferrocene derivatives) is now routine, and extensive reviews of synthetic methods have been published.4-5 In brief, one of four approaches is used to produce derivatized metallocenes (1) a... 

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