Cyclopentanone insertion into n⁹-indenyl rings of zirconium sandwich complexes

Addition of two equivalents of cyclopentanone to the bis(indenyl)zirconium sandwich compound (n⁹-C₉H₅-1,3- ⁱPr₂)(n⁵-C₉H₅-1,3- ⁱPr₂)Zr resulted in selective insertion of two equivalents of the ketone into the 1 and 4 positions of one of the indenyl ligands, and the resulting product was characterized by NMR spectroscopy and X-ray diffraction. For the mixed ring compound, (n⁵-C₅Me₅)(n ⁹-C₉H₅-1,3-ⁱPr₂)Zr, two isomeric double-insertion products were observed where C-C bond formation took place at the 1 and 4 (major) and 1 and 6 (minor) positions of the indenyl. The major product was characterized by X-ray diffraction. Deuterium labeling experiments and addition of substoichiometric amounts of ketones were used to gain insight into the preferred sites of insertion, and mono(ketone) intermediates were observed and characterized by NMR spectroscopy.