Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: synthesis, characterization, and olefin polymerization behavior

Novel Synthetic Strategy for Developing an Isospecific Unbridged Metallocene System for Propylene Polymerization

“…[17] The bonding geometry around the zirconium center, such as bond angles of Cl1-Zr-Cl2 and ring-centroid-Zr-ring-centroid, and bond lengths of Zr À Cl and Zr-ring-centroid are in the range similar to those for other nonbridged zirconocene complexes [19,29] and very similar to those of 3 [28] and [{1-(p-C 6 H 5 C 6 H 4 )-3,4-Me 2 C 5 H 2 } 2 ZrCl 2 ] (BPZr). [27] Propylene polymerization: The polymerization of propylene with zirconocenes 3, 4, and 5 was achieved at various temperatures of T p = 0, 25, 50, and 70 8C under MAO and [Ph 3 C][BA C H T U N G T R E N N U N G (C 6 F 5 ) 4 ]/TIBA activation at atmospheric monomer pressure and the polymerization results are summarized in Table 1. To compare their polymerization properties, the polymerizations with unfunctionalized "class II", [{1-(p-C 6 H 5 C 6 H 4 )-3,4-Me 2 C 5 H 2 } 2 ZrCl 2 ] (BPZr) and the well known isospecific catalyst, rac-[EtA C H T U N G T R E N N U N G (Ind) 2 ZrCl 2 ] (EBIZr) were also carried out.…”

“…[15][16][17][18][19][20][21][22][23][24][25][26] Although several reports showed that the microstructure of the produced polypropylene strongly depends on the steric and electronic effects of the substituents, as well as on the ion-pair structure of a cationic active center and a counter anion, [16,20,23,25] in most cases, the unbridged metallocenes afforded atactic polypropylene due to rapid ligand rotation. [19,27] When we consider the relative ease of synthesis of unbridged metallocenes compared to that of ansa-metallocenes, it is still of great interest to develop unbridged metallocene catalytic systems capable of inducing stereospecific polymerization of propylene. To achieve this goal, we have been pursuing the development of isospecific unbridged metallocene catalytic systems that can be generated in situ during the activation step and have designed a new "class I" of unbridged zirconocenes having Lewis basic substituents.…”

Endowing Aspecific, Unbridged‐Metallocene Propylene‐Polymerization Catalysts with Isospecificity: The Unprecedented Role of MAO

“…In particular, chiral ansa ‐metallocene catalysts, which follow an enantiomorphic site‐control mechanism, have been intensively investigated to obtain stereochemical control of propylene polymerization by varying the ligand structure 5–7. Unbridged‐metallocene‐based systems, on the other hand, have received little attention owing to their aspecific nature8, 9 in spite of their ability to produce iso‐rich10, 11 or isotactic–atactic block polypropylene12, 13 when containing rotationally hindered ligands. As unbridged metallocenes are far easier to synthesize than ansa ‐metallocenes, we have been investigating isospecific, unbridged‐metallocene catalytic systems that can be generated in situ during the activation step.…”

“…To this end, we have designed “class I” unbridged metallocenes , a new class analogous to the known aspecific, unbridged metallocenes of “class II” 8. 9 The Lewis basic sites E in class I complexes are found to interact with [Me‐MAO] − to generate rigid, rac ‐like cationic active species, thereby endowing aspecific, unbridged‐metallocene precatalysts with isospecificity. Herein, we report a novel example of a sterically unhindered, unbridged zirconocene system that is able to produce highly isotactic polypropylene through the unprecedented role of methyl aluminum oxane (MAO).…”

Dinuclear Metallocenes with a Modulated Biphenylene Bridge for Olefin Polymerization

“…The detailed structural analysis indicates that the bonding geometry around the zirconium center, such as the Cl(1)-Zr-Cl(2) and Cg(1)-Zr-Cg(2) bond angles and Zr-Cl and Zr-Cg bond lengths shown in Table 1, are in a similar range to those of mononuclear, unbridged zirconocene complexes. [28][29][30] The dihedral angle of 41.28(18) nonuclear zirconocene 4a (47.2°) [31] than that observed in the biphenylene-bridged 2a [63.6(2)°], [27] which suggests that flexible nature of the bridging group makes the steric environment of each metallocene unit of 2b similar to that of the mononuclear 4a. [a] Data taken from ref.…”