Functional Group Chemistry at the Group 4 Bent Metallocene Framework: [2+2] Cycloaddition of the Parent Bis(vinyl-Cp/vinyl-Ind)ZrCl₂ Systems

Bis(vinyl-Cp)zirconium dichloride (6) undergoes a clean intramolecular photochemically induced [2+2] cycloaddition reaction to yield the cyclobutylene-bridged ansa-zirconocene isomer (7) when irradiated with UV light (HPK 125, Pyrex filter) at ambient conditions. Both the open and the ansa-bridged isomers (6, 7) were characterized by X-ray diffraction. The corresponding bis(2-vinylindenyl)ZrCl2 complex (12) also closes rapidly and completely to the ansa-metallocene (13) upon photolysis. The bis(2-butadienylindenyl)ZrCl2 complex (20) undergoes a formal [4+4] cycloaddition reaction upon photolysis to yield its ansa-metallocene isomer 21, exhibiting an eight-membered carbocyclic bridging unit. The metallocene complexes prepared and characterized in this study give very active ethene polymerization catalysts upon activation with excess methylalumoxane.