ansa-Metallocene derivatives

Abstract

ansa-Metallocene derivatives XVII *. Racemic and meso diastereomers of group IV metallocene derivatives with symmetrically substituted, dimethylsilanediyl-bridged ligand frameworks. Crystal structure of R ,S-Me 2 Si(3-t.Bu-5-MeC s H 2) 2ZrCI2

Higher ?-olefin polymerizations catalyzed byrac-Me2Si(1-C5H2-2-CH3-4-tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

“…As a result, the reaction of Me 2 Si(1‐C 5 H 3 ‐2‐CH 3 ‐4‐ t Bu) 2 with Zr(NMe 2 ) 4 affords Me 2 Si(1‐C 5 H 2 ‐2‐CH 3 ‐4‐ t Bu) 2 Zr(NMe 2 ) 2 in 90% NMR yield ( rac / meso = 2.5/1) and pure rac ‐Me 2 Si(1‐C 5 H 2 ‐2‐CH 3 ‐4‐ t Bu) 2 Zr(NMe 2 ) 2 ( rac ‐ 1 ) in 52% isolated yield 13(c). Corresponding dichloride compound, rac ‐Me 2 Si(1‐C 5 H 2 ‐2‐CH 3 ‐4‐ t Bu) 2 ZrCl 2 , was prepared by Brintzinger et al by the reaction of Me 2 Si(1‐C 5 H 2 ‐2‐CH 3 ‐4‐ t Bu) 2 K 2 and ZrCl 4 (THF) only in 9% isolated yield 14 . In situ alkylation of ch Cp 2 Zr(NR 2 ) 2 complexes with AlR 3 followed by ionization by complexes with ammonium salts (e.g., [HNMe 2 Ph][B(C 6 F 5 ) 4 ]) or by alkyl abstraction reagents [e.g., CPh 3 , B(C 6 F 5 ) 3 ] has been proved to be an efficient procedure to activate ch Cp 2 Zr(NR 2 ) 2 for olefin polymerizations 15.…”

Stereospecific Olefin Polymerization Catalyzed by Metallocene Complexes

“…For example, group 4 metallocene chlorides barely survive the usual column chromatograph separation (although a column technique at low temperature under an inert atmosphere may give good results), and occasionally several recrystallizations are required. Introduction of bulky substituents on Cp/indenyl ligands or bridging moieties can improve the racemo/meso ratios in the synthesis of ansa-metallocenes [42,63,64,65]. Exclusive synthesis of the racemic isomer was even achieved using tert-butyl and trimethylsilyl substituents.…”

“…Extremely high isotacticity ([mmmm] > 0.99) was achieved using 3 (R 1 =Me, R 2 =1-naphthyl) [40]. Substituted cyclopentadienyl ligands bridged by a silicon atom were found to be effective for the construction of isospecific ansa-metallocenes (4, [mmmm]=0.98) [41,42].Yamazaki recently reported that furyl substituents on cyclopentadienyl rings greatly increase catalytic activity of the ansa-zirconocene and hafnocene complexes [43]. Some C 1 -symmetric ansa-metallocenes also produce isotactic polypropylene, although it is difficult to predict their stereoselectivity in the polymerization.…”

Strategies for the Synthesis of Chiral Carbon‐Bridged Group IV ansa‐Metallocenes

“…The meso ‐diastereomer was found to be formed preferentially ( rac : meso =1:1.3–1:2.0). Attaching an additional methyl group next to the bridge ( 16 – 18 ), however, could shift the selectivity towards the rac ‐isomer ( 19 – 21 ), an effect that had previously been observed for silylene‐bridged metallocenes . A bis‐2‐ tert ‐butyl‐4‐isopropylcyclopentadienyl derivative gave even a 3:1 rac : meso mixture in 40 % yield .…”