Synthesis and reactivity of metallocene complexes for olefin polymerization

Abstract

The unbridged zirconocenes, $(RInd)_2ZrCl_2$ [R = 1- (II-3) or 2-Tol (II-4), Ind = indenyl, Tol = p-tolyl] have been prepared from the reactions of $ZrCl_4$ with lithium salts of 1-p-tolylindene and 2-p-tolylindene in diethyl ether. Complex II-3m catalyzes the polymerization of propylene in the presence of methylaluminoxane (MAO) to afford syndiotactic-dominant polypropylene (PP) having a short syndiotactic length at -30℃, whereas II-3r and II-4 produce atactic PPs under similar conditions. ansa-Ligands, $Me_2Si(RInd)_2$ [R = 2 (III-1) and 3-Tol (III-2)], have been prepared as a mixture of rac- and meso-isomers in a ratio of 1:1 from the reactions of $Me_2SiCl_2$ with cyanocuprates of 1-p-tolylindene and 2-p-tolylindene in diethyl ether, respectively. Pure rac-isomers, III-1r and III-2r, have been isolated by fractional recrystallization of III-1 and III-2. Thermal diastereomerization of III-1 and III-2 between rac- and meso-isomers has been studied by $^1H$ NMR spectroscopy. Symmetric ansa-zirconocenes, $Me_2Si(RInd)_2ZrCl_2$ [R = 2 (III-3) and 3-Tol (III-4)] have been prepared from the reactions of the corresponding dilithiated ligands with $ZrCl_4$ in ether/hexane at -78℃. Complex III-3r has a crystallographically imposed $C_2$ symmetry with Zr and Si atoms on the $C_2$ axis as observed in its single crystal X-ray structure. In propylene polymerization complex III-3r produced highly isotactic PP at 0℃ by the enantiomorphic site control mechanism, and III-4m afforded syndiotactic-dominant PP having a rr triad of 49% at -30℃ by the chain end control mechanism. Asymmetric ansa-zirconocenes, $Me_2X$(Cp)(3-TolInd)$ZrCl_2$ [X = C (IV-4), Si (IV-5)] and $Me_2Si$(Cp)(2-TolInd)$ZrCl_2$ (IV-6), have been prepared by the reactions of $ZrCl_4$ with the corresponding lithiated ligands in diethyl ether at -78℃. The molecular structure of IV-6 shows that the p-tolyl substituent is oriented in the lateral sector of the opposite direction to six-membered ring of indenyl liga...