Manipulation of the Ligand Structure as an Effective and Versatile Tool for Modification of Active Site Properties in Homogeneous Ziegler-Natta Catalyst Systems

The First Fluorenyl ansa-Yttrocene Complexes: Synthesis, Structures, and Polymerization of Methyl Methacrylate

“…The smaller angle between the C bridgehead −Si bond and the π-ring plane for the fluorenyl ring (11.8(10)°) than for the Cp‘ ring (18.7(11)°) indicates that the strain at the bridgehead carbon atoms of the π-ring planes is reduced for the fluorenyl ring compared with the Cp‘ ring. The acute dihedral angle of 69.9° between two π-ring planes is somewhat larger than those observed in other Si-bridged bent metallocenes. 12c, The YCl 2 Li rhombus is nearly planar. The Cl−Y−Cl angle of 88.04(16)° and bond parameters around Li + fall within ranges similar to those observed in other Cp* 2 MCl 2 LiL 2 types of complexes, 5e,,11c, indicating that the change in the chelating ligands around the rare-earth center has little influence on the bonding sphere of the ether-coordinated Li + ion.…”

“…To partially overcome this problem and to investigate the role of a π-ligand in governing the overall molecular geometry and electronic properties of organo-rare-earth-metal complexes, many efforts have been made toward substituted ring systems such as permethylated cyclopentadienyl , or indenyl 5b, and their ansa analogues . Nevertheless, the synthesis, structure, and investigation of the catalytic effect of the fluorenyl congener, which in turn has played a unique role in group 4 metallocene catalyst systems in olefin polymerization reactions, have not been properly elucidated yet. The only reports have been the synthesis and the structural characterization of bis(fluorenyl) divalent samarium complexes and the synthesis of poly(fluorenyl) complexes of trivalent yttrium 14a and lanthanides, 14b,c none of which have been structurally clarified.…”

A Combined ab Initio MO−MM Study on Isotacticity Control in Propylene Polymerization with Silylene-Bridged Group 4 Metallocenes. C2 Symmetrical and Asymmetrical Catalysts

“…The steric energy difference between the most favorable mode with the next most favorable mode, 12.2 kcal/mol in the propagation state, suggests that the stereoregulating ability of Zr 3a should be very good, comparable to that of Zr 1e having 2-methyl-4-isopropylindenyl. Razavi and co-workers found experimentally that Zr 3 having a methyl group at the 3-position of the Cp ring gives a hemiisotactic sequence . It is expected from the above MM result that the methyl substituent, unlike the tert -butyl in Zr 3a , cannot preclude the insertion of monomer from the less-hindered site in the propagation step which would produce mainly r diad in alternate sequences.…”

Ethene/propene copolymerisation by [Me2C(3-RCp)(Flu)]ZrCl2/MAO (R = H, Me,isoPr,tertBu)

“…The parameters are almost identical to the ones reported by Fink. Nevertheless using our procedure a comparison of the models by comparing SSR' is possible: SSR' = SSR/(number of responses-number of parameters) (25) As reported in Tab. 7 the SSR' for the penultimate model is about an order of magnitude smaller.…”