A New Class of Zirconocene Catalysts for the Syndiospecific Polymerization of Propylene and Its Modification for Varying Polypropylene from Isotactic to Syndiotactic

C2-Symmetric Zirconocenes for High Molecular Weight Amorphous Poly(propylene)

“…As already pointed out in a previous paper, [20] the prediction that ansa C 2 -symmetric zirconocenes in which the chirality of the p-ligand is (R,R) generally favor the insertion of re propene, which received several experimental confirmation, [21,22] is in this case reversed: singlecarbon bridged C 2 -symmetric, (R,R)-bis(3-R9-1-Ind) zirconocenes, with R > CH 3 , are likely to select the si propene enantioface, due to the stronger orientating effect the R group has on the growing chain with respect to the indenyl six-membered ring. Moreover, the non-bonded interactions between the methyl group of the monomer and a tert-butyl group are also minimized when the propene coordinates with its si enantioface.…”

Syndiotactic Polymerization of Propylene: Single-Site Vanadium Catalysts in Comparison with Zirconium and Nickel

“…Example compounds include bis(dimethylsilyl)-1,19,2,29-diyl(39,59-diisopropyl)(4-isopropylcyclopentadienyl)zirconium dichloride, bis(dimethylsilyl)-1,19,2,29-diyl(39,59-diisopropyl)(4-trimethylsilylcyclopentadienyl)zirconium dichloride, [6,60] and g 1 ,g 5 -tert-butyl(2,7-bis-tert-butylfluorenyldimethylsilyl)amidodichlorotitanium (see Figure 21). [54,58] It is worth noting that C s symmetry of the precatalyst is necessary but not sufficient in order to promote syndiotactic-specific polymerization of propylene.…”

Metallocenes

“…Many different variations of bridging groups have been explored. The Buchwald and Bercaw groups have reported (28,29) syndiospecific and other polypropylene polymerizations using complexes with two bridges tying the Cp rings together (1). Complexes with especially constrained bridges such as 2 have very high comonomer incorporation rates (30).…”

“…For example, propylene polymerization by 64 is predominantly syndiospecific at low temperatures and high monomer concentrations, but moderately isospecific at high temperatures and low monomer concentrations. The change in stereoselectivity is explained by rotation of the bulky top substituent on a timescale similar to polymer chain generation (29). Either pattern D or F is accessible, depending on the rotation kinetics of the -CH(Me)(t-Bu) substituent relative to olefin insertion.…”