Preparation of the ansa-Zirconocenes with an N-Methylpiperidine Bridge

Bridged ligands 4,4-di(cyclopentadienyl)-N-methylpiperidine (4) and 4,4-di(indenyl)-N-methylpiperidine (5) were prepared by condensation of cyclopentadiene or indene with N-methylpiperidone. Dilithium salts 4a and 5a were subsequently transformed into the corresponding ansa-zirconocenes 2 and 3. No direct contact Zr···N was found in the crystal structure of 2. The attempt to prepare zirconocene 3 from distannyl derivative 5b gave an unexpected monoindenyl complex 6 comprising one unreacted stannylated indenyl group and having direct coordination of Zr by nitrogen.