ansa-Metallocene derivatives XXXIII. 2-Dimethylamino-substituted bis-indenyl zirconium dichloride complexes with and without a dimethylsilyl bridge: syntheses, crystal structures and properties in propene polymerization catalysis

Abstract

Bis(2-N,N-dimethylamino-indenyJ) zirconium dichloride, (2-(CH 3)2 N-C 9 H 6)2 ZrC1 2 • and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride. (CH3)2Si(2-(CH3)2N-C9Hs)2ZrCI2' were prepared by reaction of the corresponding ligand lithium salts with ZrCl" in toluene. Diffractometric structure determinations reveal C 2-symmetrlc complex geometries for both complexes. An increased electron density at the Zr center of the dimethylamino-substituted complexes is indicated by reduction potentials which are 0.3-0.4 V morr negative than those of their unsubstituted analogs. When activated with methyl aluminoxane in toluene solution. (CH3)2Si(2-(CH3)2N-C9Hs)2ZrCI2 catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Mel Si-bridged bis(indenyJ)ZrCl 2 complexes. but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and AI-Me species.

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

“…Likewise, the diastereocontrol in favor of the racemic isomer in the metallation step is inferior to that observed for the ethylenebridged analogues. The 1 H NMR chemical shift of β-H in rac-44 (δ ϭ 6.22 ppm) is of the same magnitude as that observed for the 2-dimethylamino-substituted analogue rac-8 (δ ϭ 6.4 ppm) [38] (vide supra) and strongly shielded relative to that observed for the parent rac-dimethylsilylenebis(-indenyl)zirconium dichloride (δ ϭ 6.90 ppm).…”

“…Excluded thus from detailed discussion are complexes containing substituted or unsubstituted cyclopentadienyl, fluorenyl and related ligands, complexes with pendant heteroatom substitution where the functional group is separated from the ligand by an inert linker, [22Ϫ25] as well as complexes with directly bonded phosphorus, [26] boron, [27Ϫ29] and other heteroatom substituents. The so-Since the first reports by Brintzinger, [38] Näsman, [39] and Plenio groups [40] in 1996, a number of 2-amino-substituted bis(indenyl) complexes of titanium and zirconium have been described and characterized (complexes 8Ϫ16).…”

“…In the case of the dimethylsilylene-bridged complex 8, the reaction in toluene gives a 7:2 rac/meso mixture in an overall yield of 57%, from which the pure racemic diastereomer rac-8 was obtained in 30% yield by recrystallization, and was characterized crystallographically. [38] The ethylene-bridged analogue 9 in turn shows an unusual case of solvent-dependent meso diastereoselectivity in the metallation step, to yield a 1:1 rac/meso ratio in tolu-ene, from which rac-9 was isolated after fractional crystallization in 33% yield. [39] However, when the metallation was carried out in THF, a 3:7 rac/meso ratio was obtained from which the pure meso diastereomer was isolated in 38% yield.…”

“…[40,44,49,52] For 2-(dimethylamino)indene, the synthesis of both dimethylsilylene- [38] and ethylene-bridged [39] bis(indenyl) analogues 18 and 19 in good yields (59 and 77%, respectively) has been described that employs standard deprotonation/ alkylation and deprotonation/silylation procedures in THF or diethyl ether solution (Scheme 1). The synthesis of 3-aminoindenes by enamine reaction of 1-indanone with secondary amines has also been reported.…”

“…[69] Brintzinger and co-workers have reported cyclic voltammograms of the dimethylamino-substituted complexes rac-8 and 11. [38] In comparison with the unsubstituted analogues rac-dimethylsilylenebis(indenyl)zirconium dichloride and bis(indenyl)zirconium dichloride, an additional irreversible oxidation peak was observed at E 1/2 ഠ 0 V, indicating instability against oxidation. The Zr IV /Zr III reduction peaks of these complexes, recorded at E 1/2 ϭ Ϫ2.48 V (rac-8) and Ϫ2.42 V (11), respectively, are shifted to more negative potentials by 0.28 and 0.43 V relative to the unsubstituted analogues, indicating noticeable increase in the electron density at the Zr centers of the amino-substituted complexes.…”