Ansa-metallocenes by intramolecular ring closure reactions - Syntheses and applications

Examples of a functional group chemistry at the Group 4 bent metallocene frameworks are presented and discussed that allow for the preparation of ansametallocenes at the stage of the intact organometallic complexes. These examples include ansa-metallocene formation by means of intramolecular olefin metathesis reactions, by photochemical [2+2] cycloadditions of pendant olefinic moieties and even of a Mannich-type carbon carbon coupling reaction of enamino substituents attached at the Cp-rings. Many of the resulting ansa-metallocene systems were employed as components of reactive homogeneous Ziegler-Natta olefin polymerization and copolymerization catalysts. The Mannich coupling reaction was also used in ([3])ferrocenophane chemistry, eventually leading to novel chelate ligand systems that were employed in catalytic asymmetric polyketone formation.