Isospecific Propylene Polymerization with a Novel 2-Substituted Bis(indenyl) ansa-Zirconocene

Abstract

The preparation and crystal structure of the first group 4 ansa-metallocene with an oxygen atom directly bonded to the 2-position of an η5-indenyl moiety, rac-[ethylenebis(2-(tert-butyldimethylsiloxy)indenyl)]zirconium dichloride (3), is reported. In combination with methylaluminoxane (MAO), complex 3 polymerizes propylene to highly isotactic crystalline polypropylene (T m = 148 °C; M w = 19 000; M w/M n = 2.4). Under similar conditions, the propylene polymerization activity of 3/MAO exceeds that of the conventional ansa-metallocene catalyst system (dimethylsilyl)bis(4,5,6,7-tetrahydroindenyl)zirconium dichloride (4)/MAO by a factor of 2 (5300 vs 2300 kg of PP/mol of Zr/h; Tp = 20 °C; P(C3H6) = 2.0 bar; [Al]:[Zr] = 3 000:1). Complex 3 crystallizes in the unusual indenyl-backward conformation. The molecular structure is consistent with the expected C 2 symmetry.

Metallocenes

“…While relatively unreactive substituents such as alkyls and aryls are most prevalent, siloxide (14) and amide (15) groups have been appended to Cp rings; Lewis acids such as Al atoms in MAO may reversibly coordinate to these heteroatoms (16).…”

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

“…[104][105] The synthesis of 2-trialkyl/arylsiloxysubstituted indenes utilizing the keto-enol tautomerism of 2-indanone [73] is shown in Scheme 13. Thus, reaction of 2-indanone with tert-butylchlorodimethylsilane, [85] chlorodimethyl(thexyl)silane, [93] chlorotriisopropylsilane, [90] chloro-(cyclohexyl)dimethylsilane, [106] and tert-butylchlorodiphenylsilane using the base/solvent combinations of DMF/ imidazole or DBU/benzene gave the corresponding 2-siloxyindenes 64Ϫ68 as distillable oils in 69Ϫ90% yields. The six-membered ring substituted ligand analogues 2-(tertbutyldimethylsiloxy)-4,7-dimethylindene (69) [91] (distillable oil) and 2-(tert-butyldimethylsiloxy)cyclopenta[l]phenanthrene (70) [89] (powderous solid) were prepared in 85 and 72% yields, respectively, by reaction of 4,7-dimethyl-2-indanone [91] and 1,3-dihydro-2-oxocyclopenta[l]phenanthrene [107,108] (Scheme 14) with tert-butylchlorodimethylsilane/DBU in benzene.…”

“…In contrast to bis(indenyl)ethane for which the 3,3Ј-indenyl-bridged isomer predominates, [10,66,118] all siloxy-substituted indenes yield exclusively the 1,1Ј-bridged product. [85,90,93,106] Only in the case of the six-membered ring substituted 2-siloxyindenes 69 [91] and 70 [106] were the yields for the ethylene-bridged bis(indenyl) ligands 79 and 80 ( Figure 10) low (4.8 and 3.9%, respectively), which resulted from the nearly exclusive predomination of the spirocyclopropane adducts formed by intramolecular bis(alkylation) reactions of the substituted indene. [8,67,77,119] Both 2-(tert-butyldimethylsiloxy)indene (64) and 2-[dimethyl-(thexyl)siloxy]indene (65) were further converted into the dimethylsilylene-bridged bis(indenyl) ligand analogues 81 and 82 in high yields by deprotonation with nBuLi followed by reaction with 0.5 equiv.…”

“…[85,90,93,97] The bulkiness of the siloxy group in the α-position to the ethylene bridge influences the rac/meso ratio of the metallocenes formed. In the case of the 2-tertbutyldimethylsiloxy-substituted complex 42, metallation with ZrCl 4 in THF initially produces a rac/meso ratio of 14:1 as determined by 1 H NMR spectroscopic analysis of the crude product, whereas an entirely rac-selective metall-Scheme 21.…”

“…Synthesis of the ethylene-bridged 2-siloxy-substituted bis(indenyl)-and bis(tetrahydroindenyl)metallocene complexes 42, 43, 45Ϫ47, 49 and 50; for racemic complexes only one enantiomer of the racemic pair is shown ation was observed for the 2-triisopropylsiloxy-substituted analogue 49. Pure rac-42 was obtained in 21Ϫ26% yield after crystallization/recrystallization from dichloromethane, [85,97] and pure meso-42 after repeated recrystallization from a large-scale synthesis of 42. [97] The analogous hafnium complex rac-43 was isolated in 13% yield according to a similar procedure.…”