Aminofluorenyl−Pentamethylcyclopentadienyl and Bis(aminofluorenyl) Derivatives of Group 4 Metals

Abstract

New group 4 compounds containing a 9-(dialkylamino)fluorenyl ligand have been prepared, and their properties and reactivities have been briefly investigated. Single-crystal X-ray analysis of {9-(N,N-dimethylamino)fluorenyl}_2ZrCl_2 (4) reveals strong zirconium−nitrogen dative bonds. The asymmetric unit contains two molecules with an unusual coordination of aminofluorenyl ligands, best described as comprised of a strong Zr−N dative interaction and essentially an η^1-fluorenyl coordination, supplemented by a weak additional C C dative interaction of one double bond of one of the benzo units. The barrier to rotation around the C−N bond of {9-(N,N-diisopropylamino)fluorenyl}(pentamethylcyclopentadienyl)ZrCl_2 (9) has been determined:  ΔG⧧(−25 °C) = 11.1 kcal·mol^(-1). Unlike related aminoborollide complexes, aminofluorenyl complexes resist quaternization by alkyl halides. Several aminofluorenyl complexes have been tested for propylene polymerization behavior in the presence of methylaluminoxane (MAO); atactic polypropylene is obtained with very low activities. The syntheses of 9-(dialkylamino)fluorene compounds are described, as are the syntheses of group 4 compounds via the corresponding 9-(dialkylamino)fluorenide lithium salts.