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.

Recent Advances in the Chemistry of Pentafulvenes

“…40 During the course of the synthesis of a homogeneous Ziegler catalyst for polymerization, Erker and co-workers effectively utilized a previous literature procedure by Hafner for the synthesis of 6-amino-6-methylfulvene and some derivatives. 64,65…”

“…During their synthesis of imidazolium-substituted metallocenes, Kunz et al prepared imidazoline-based fulvenes ( 5 , see section ) as precursors by using a modified version of the route used by Meerwein and Hafner . During the course of the synthesis of a homogeneous Ziegler catalyst for polymerization, Erker and co-workers effectively utilized a previous literature procedure by Hafner for the synthesis of 6-amino-6-methylfulvene and some derivatives. , …”

How to synthesize a constrained geometry catalyst (CGC) – A survey

“…Dianionic ethylene-bridged ligand systems may be formed by milder deprotonation with NEt 3 before subsequent reaction with TiCl 4 gives the corresponding complexes in high yields [23] (Scheme 6). In the case of methylene-bridged CGCs, bis(amido)dichlorocomplexes such as Zr(NEt 2 ) 2 Cl 2 (THF) 2 and Ti(NMe 2 ) 2 Cl 2 proved to be successful [24][25][26].…”

The (butadiene)metal complex/B(C6F5)3pathway to homogeneous single component Ziegler–Natta catalyst systems

“…The dimethylsilanediyl-bridged Cp/amido group 4 metal complexes, the 'constrained geometry' catalyst precursors, 26,27 show a similar chemistry. Reaction of the (s-cis-h 4 -butadiene)Zr(Cp*SiMe 2 NR) system 14 28 16) 32 to initially yield the cisoid adduct 17 (see Scheme 5).…”