Formation of a Constrained-Geometry Ziegler Catalyst System Containing a C1 Instead of the Usual Si1 Connection Between the Cyclopentadienyl and Amido Ligand Components

Abstract

6-Amino-6-methylfulvene (4) is cleanly N-acylated by treatment with pivaloylchloride/triethylamine to give the fulvene (C5H4)=C(CH3)NHCOCMe3 (5c). Treatment of 4 with trimethylchlorosilane similarly yields the mono-N-silylated fulvene (C5H4)=C(CH3)NHSiMe3 (7). Both 5c and 7 are cleanly doubly deprotonated e.g. by treatment with LDA to give ligand systems [(C5H4)C(=CH2)NR]Li2 [8a (R = COCMe3) and 8b (R = SiMe3), respectively]. Their treatment with MCl4 · 2 THF (M = Ti, Zr) yield the spiro-metallocenes [(C5H4)C(=CH2)NR]2M (9, 10). Complex 10a (M = Zr, R = COCMe3) was characterized by X-ray diffraction. The reaction of 8a with (Et2N)2ZrCl2 in THF gives rise to the formation of [(C5H4)C(=CH2)NCOCMe3]Zr(NEt2)2 (11) (70 % isolated), and the reaction of 8b with (Et2N)2ZrCl2 yields [(C5H4)C(=CH2)NSiMe3]Zr(NEt2)2 (12) (76 % isolated). Treatment of complex 12 with an excess of methylalumoxane (MAO) in toluene solution results in the generation of an active homogeneous Ziegler catalyst for the polymerization of ethene. A comparison with the usually employed [(Me5C4)SiMe2NCMe3]ZrCl2/MAO “constrained-geometry” Ziegler catalyst system reveals a similar catalyst activity and performance of this novel type of a C1-bridged “constrained-geometry” catalyst as it is exemplified by the [(C5H4)C(=CH2)NSiMe3]ZrX2 (12)/MAO combination.