Dual-Side ansa-Zirconocene Dichlorides for High Molecular Weight Isotactic Polypropene Elastomers

Abstract

The four new asymmetric ansa-zirconocene dichlorides rac-[1-(9-η 5 -fluorenyl)-2-(2-phenyl-1-η 5 -indenyl)ethane]zirconium dichloride (4c), rac-[(9-η 5 -fluorenyl)(5,6-cyclopenta-2-methyl-1-η 5 -indenyl)dimethylsilane]zirconium dichloride (4d), rac-[(9-η 5 -fluorenyl)(2-methyl-1-η 5indenyl)dimethylsilane]zirconium dichloride (4e), and rac-[(9-η 5 -fluorenyl)(2-phenyl-1-η 5indenyl)dimethylsilane]zirconium dichloride (4f) have been prepared, and their polymerization behavior was compared to the recently published rac- 4b). The Si-bridged ligands are easily accessible by the reaction of fluorenyllithium with dimethyldichlorosilane and the subsequent addition of indenyllithium. A similar route using 1-(9-fluorenyl)-2-bromoethane was applied for the synthesis of the ethylene-bridged ligands. The Zr(IV) complexes of all ligands are highly active catalysts for the propene polymerization reaction after activation with MAO. The influence of the bridge and the particular substitution pattern of the indenyl fragments has been studied with respect to monomer concentration and polymerization temperature. The exchange of the ethylene bridge by a dimethylsilane unit results in a strong increase of the molecular weights but also in a decreased polymerization activity deriving from a fast decomposition of the active catalyst species. Interestingly, significantly higher polymer molecular weights could be found for the complexes that contain the 5,6-cyclopentyl substituent on the indenyl moiety. All catalysts showed the effect of a declining stereoselectivity with increasing monomer concentration, leading to the formation of homopolypropene elastomers. The mechanism of stereoerror formation of these C 1 -symmetric species was investigated by deuterium labeling studies on the propene monomers and by comparison with C 2 -symmetric complexes.

Metallocene Catalysts for 1‐Butene Polymerization

“…Screening of C 1 -Symmetric Metallocenes C 1 -symmetric metallocenes, bearing one ligand endowed with bilateral symmetry such as fluorenyl (Flu) [25] or dithienocyclopentadienyl (S 2 -), linked to one substituted cyclopentadienyl (Cp) [26] or indenyl (Ind), [27] have been shown to allow access to poly(propylene)s in a wide range of isotacticity, that is melting point and crystallinity.…”

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

“…However, the presence of LiCl in the catalysts does not seem to affect their catalytic properties: for example, MAO/metallocene toluene solutions do not lose their activity over time for several days, and slowly separate the LiCl powder. Complexes 11,13,16,19,21, and 22 were activated with MAO and used in polymerization without removing LiCl.…”

“…The microstructures of selected PP samples were investigated by 13 C NMR. The experimental (Table 9 and 11) and calculated (Table 10 and 12) triad and pentad distribution of selected samples are given together with the enantiomorphic triad test E, the isospecific average Bernullian probability parameter b and the average length of isotactic blocks, hL iso i.…”

“…[3] This concept, first developed by Ewen for the synthesis of hemiisotactic and isotactic PP, [1,3] has been later employed for the production of elastomeric PP [4][5][6][7][8][9][10][11][12][13][14][15][16] and alternating C 2 C 3 copolymers of different microstructures. [9] So far, the most interesting complexes of this class are those based on combinations of fluorene and substituted indenes, since they couple synthetic simplicity to the steric variability of indene.…”

“…In addition to the occasional discrepancy of results coming from different laboratories, several other features of these complexes are worth noting: the very broad range and fine tunability of stereoselectivities and the high regioselectivity of these complexes, the reported instability of Me 2 Si(2,4,7-Me 3 -Ind)(9-Flu)ZrCl 2 [12] and other similar Sibridged complexes, [13,17] contrasted by the better stability and performance of the (synthetically more complex) ethylene bridged complexes, and, in general, the low molecular weights of the polypropylenes obtained from such complexes. This latter feature has a few notable exceptions: the high molecular weight PP reported for Me 2 C(3-t BuInd)(9-Flu)ZrCl 2 /Al i Bu 3 /Ph 3 CB(C 6 F 5 ) 4 , 214 000 at 50 8C in liquid propylene, [11] the very high molecular weights of the lowisotacticity PP produced with a trityl borate activated hafnocene, ethylene(2-methyl-5,6-cyclopentylindenyl)(9-fluorenyl)HfMe 2 [16] and the high molecular weight and high isotacticity obtained by Razavi with the Me 2 C(2-Me-4-t BuCp)(9-Flu)ZrCl 2 complex.…”