Asymmetric Metallocene Catalysts Based on Dibenzothiophene:  A New Approach to High Molecular Weight Polypropylene Plastomers

Abstract

Synthesis and polymerization data of a series of new sulfur-containing C 1 -symmetric metallocenes,rac-[1-(9-η 5 -fluorenyl)-2- (8), are reported. The characteristic structural feature of these complexes is the 2-methyl-1H-benzo[b]indeno[4,5-d]thiophene moiety (3: MBIT), which was derived from dibenzothiophene. In the case of 7a-c the MBIT unit shows a "back" orientation, whereas in 8 it is directed to the "front" of the tetrahedral metallocene dichloride species, which was unambiguously illustrated by X-ray structure analysis. Propylene polymerization experiments revealed higher activity and stereoselectivity for 7a/MAO compared to 8/MAO. The catalysts 7a,8/MAO were found to operate under different polymerization mechanisms indicated by a diverse correlation of tacticity and polymerization temperature. Crystalline, flexible polypropylenes with tacticities ranging from 65 e [mmmm] e 90 and molecular weights up to 2 × 10 5 g mol -1 were obtained for 7a/MAO, whereas experiments using 8/MAO produced low tacticity, waxy materials. To achieve ultrahigh molecular weight isotactic polypropylene plastomers (M w up to 1.5 × 10 6 g mol -1 ), further investigations on the hafnium dimethyl complex 7c/[(C 6 H 5 ) 3 C + ][(C 6 F 5 ) 4 B -] in liquid propylene were performed.

Control of Ultrahigh Molecular Weight Polypropene Microstructures via Asymmetric “Dual‐Side” Catalysts

“…General Procedure The synthesis of the C 1 -symmetric catalysts, 1, 2 and 3 were reported previously [3][4][5] .…”

“…Therewith it is expected to develop a construction kit that possibly enables to anticipate different fields of polypropene material properties, especially for the new ultrahigh molecular weight species. The finding that the 5,6-cyclopentyl group represents a key success for the production of high molecular weight, elastomeric polypropene directed our further interest to a 6,7-substitution bearing sulphur atoms in the indenyl moiety [4] (2, Fig. 2).…”

C1‐Symmetric Heterocyclic Zirconocenes as Catalysts for Propylene Polymerization, 2

“…[20] Ind-Flu ligands bearing heterocycles condensed to the 4,5, 5,6, or 6,7 positions of indene have also been reported [21,22] (Table 2).…”

“…[22] [22] [22] [21] [21] [21] C 1 -Symmetric Heterocyclic Zirconocenes as Catalysts for Propylene Polymerization, 2 discussed in the section '' 13 C NMR Analysis and Correlation with Thermal and Solubility Data. ''…”

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

“…Preparation of C 1 -symmetric, mixed-ligand ethylenebridged group 4 ansa-metallocenes (Zr, Hf) 94Ϫ97 containing one benzothiophene-fused indenyl ligand and one fluorenyl ligand was recently described by Rieger (Figure 12). [129] The 2-methyl-1-H-benzo[b]indeno [4,5-d]thiophene (98) precursor was prepared in good yield by FriedelϪCrafts acylation of dibenzothiophene with methacrylic chloride in a manner similar to that described for the 5,6-ethylenedioxyfused ligand (Scheme 10), followed by subsequent Nazarov cyclization, ketone reduction and water elimination (Scheme 25). The mixed-ligand complexes, upon activation with MAO, form high-performance catalysts for production of controlled tacticity polypropylenes.…”