Building bridges: ansa-Metallocene construction by carbon-carbon coupling reactions at preformed Group 4 bent metallocene frameworks

A number of methods by which various functional groups that are attached at the Cp-rings of Group 4 bent metallocenes can be intramolecularly coupled to yield ansa-metallocenes are presented and discussed. These methods include pathways of metallacyclopentane formation from Cp-alkenyl moieties, olefin metathesis reactions between α-olefins attached at the Cp-ligands, photochemically induced [2 + 2]cycloadditions of substituted vinyl groups and Lewis acid- or Brønsted acid-catalyzed Mannich-type condensation reactions between 1-aminoethenyl functional groups at the bent metallocene framework.