ansa-Zirconocenes Based on N-Substituted 2-Methylcyclopenta[b]Indoles:  Synthesis and Catalyst Evaluation in Liquid Propylene Polymerization

Abstract

Cyclopenta[b]indole-based ansa-zirconocenes were prepared and studied as catalysts for propylene polymerization. Substituted 2-methyl-4-R-1,4-dihydrocyclopenta[b]indoles (R = Ph, 7a; R = o-Tol, 7b; R = Me, 7c) were synthesized and converted into the racemic forms of the corresponding ansa-zirconocenes Me2Si(2-Me-4-R-cyclopenta[b]indolyl)2ZrCl2 (R = Ph, 10a; R = o-Tol, 10b; R = Me, 10c). The structure of 10a was determined by X-ray analysis. The effectiveness in polymerization catalysis of the metallocenes compared to benchmark metallocenes rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (11) and rac-Me2Si(2-Me-4,5-BzInd)2ZrCl2 (12) was investigated in liquid propylene at 70 °C. Both 10a and 10b with MAO cocatalyst afforded highly isospecific (mmmm 95.9, 95.6%, respectively) and highly regisospecific polypropylene (0.17, 0.34% imbedded regioerrors), which exhibited a high melting point (T m2 = 154.2, 156.3 °C). The polymer properties were intermediate between those of 11 and 12, with the molecular weight, stereospecificity, and melting point increasing in the order 12 < 10a,b < 11. Although activities 1−2 orders of magnitude lower than for 11 and 12 were found at high MAO/Zr ratios, at low cocatalyst levels activities were similar. 10a,b were also successfully activated with alternative aluminoxanes based on branched alkylaluminums (e.g. Al(CH2CHMePh)3, obtained from α-methylstyrene), with measured activities up to 16.6 TON/((g of Zr) h) (10a/AKO). Surprisingly, no consistent effect on polymer properties of varying either the 4-aryl substituent of the cyclopenta[b]indole group or the cocatalyst was found.

Recent research progress in influence of the ansa-zirconcene catalytic system on the polypropylene microstructure

“…At very low concentrations of aluminoxanes/12, the stereoselectivity of the catalytic system increased in the order MAO < AOO < QO < AKO. In contrast, stereoselectivity increased in the order AKO < AOO < QO at high aluminoxanes/12 [13]. Seraidaris et al [37] investigated the effect of the co-catalysts of MAO and MAO/TIBA on the tacticity of polypropylene and found that the tacticity of polypropylene with Me 2 Si(2-Me-PhInd) 2 -ZrCl 2 /MAO (Al/AMO = 2400) was lightly lower than that of Me 2 Si(2-Me-Ph-Ind) 2 −ZrCl 2 /MAO/-TIBA (Al/AMO = 1500 : 1, Al/TIBA = 900 : 1).…”

“…Van Baar et al [13] reported the preparation of highly isospecific (mmmm 95.9, 95.6%) and region-specific polypropylene (0.17-0.34% imbedded regiorrors) in liquid propylene at 70…”

“…At very low aluminoxanes/12 ratios (aluminoxane/Zr = 500) with TIBA (1.0 mmol) as autoclave scavenger, the activity with MAO was approximately equal to that of AOO and QO; nevertheless, the catalyst activity with AKO did decrease greatly. When the catalytic system are of high aluminoxanes/12 ratios, the activity of catalysts increased in the order QO < MAO, AOO < AKO [13].…”

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

“…Synthesis of 5,6-dimethoxyindene (36) The dimethylsilylene-bridged analogue rac-29 has been reported in the patent literature only. It was obtained by deprotonation of the dimethylsilylene-bridged ligand precursor with nBuLi and subsequent reaction of the isolated dilithium salt with ZrCl 4 in CH 2 Cl 2 to give, after workup and crystallization from the same solvent, a 3:1 rac/meso mixture in 35% yield.…”

Isospecific Propylene Polymerization Behavior of Lewis Base Functionalized Unbridged Zirconocences under Bulk Conditions

“…The commercial production of iPP has mainly focused on the increase in molecular weight (M w ) and isotacticity of polypropylene, as well as the increase in catalytic activity by the change of catalyst structure. [3][4][5][6] Although many elaborated catalyst structures suitable for commercial iPP have been reported, [7][8][9][10][11][12][13][14] the synthetic procedures towards such C 2 -symmetric catalysts usually require many difficult steps giving rise to the increase in catalyst costs during the course of commercialization of iPP products. The high cost has been one of the principal reasons why the portion of metallocene-iPP products is below 1% of the total iPP market.…”