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 ansa‐metallocenes 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 3ferrocenophane chemistry, eventually leading to novel chelate ligand systems that were employed in catalytic asymmetric polyketone formation.