Preparation of the <i>a</i><i>nsa</i>-Zirconocenes with an <i>N</i>-Methylpiperidine Bridge

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