New bridged zirconocenes for olefin polymerization: Binuclear and hybrid structures1Dedicated to Professor Dr. Gottfried Huttner on the occasion of his 60th birthday.1

Alkylidenverbrückte dissymmetrische zweikernige Metallocenkomplexe als Katalysatoren für die Ethylenpolymerisation

“…Petersen und Royo synthetisierten eine Serie von zweikernigen Metallocenkomplexen wie etwa [Cl 2 (g-C 5 H 5 )Zr{l-C 5 H 4 (SiMe 2 )C 5 H 4 }Zr(g-C 5 H 5 )Cl 2 ] und zeigten Struktureigenschaften dieser Komplexe auf [21][22][23][24]. Spaleck beschrieb dinukleare Metallocenkomplexe f€ ur die Darstellung von isotaktischem Polypropylen [25]. Zweikernige Metallocenkomplexe mit 2,2-Cyclopentadienyl-Indenyl-Propan und Cyclopentadienyl-indenyldimethylsilan als Ligandvorstufen wurden von Green auf ihr Ethylen-und Propylenpolymerisationspotential getestet [26,27].…”

Dinuclear Metallocenes with a Modulated Biphenylene Bridge for Olefin Polymerization

“…Most of these catalyst systems, however, involve mononuclear complexes, as dinuclear systems that consist of two active centers linked within the same molecule have become a focus of attention only since the first report by Mülhaupt et al [7] on a phenylene-bridged dinuclear zirconocene system for propylene polymerization. Initial efforts made by several groups have shown that these catalyst systems are effective in olefin polymerization [8][9][10][11] but they have still remained much less defined in terms of structural aspects, class of catalysts, and kinds of polymerization they can perform in comparison with the well-known mononuclear systems.…”

Investigation of Dynamic Intra‐ and Intermolecular Processes within a Tether‐Length Dependent Series of Group 4 Bimetallic Initiators for Stereomodulated Degenerative Transfer Living Ziegler–Natta Propene Polymerization

“…[1][2][3] In this regard, the tethering of two active metal propagating centers within a bimetallic molecular framework has long been a strategy pursued with the expectation that nuclearity and cooperativity effects between two metal centers that are physically held in close proximity to one another might serve to provide access to different mechanistic processes that are competitive with propagation, and thereby, increase the scope of polyolefin compositions that are available through modulation of their relative rates . [4][5][6][7][8] However, only very recently have Marks and co-workers [4] , and subsequently, Noh and co-workers [5] succeeded in achieving this goal for PE-based co-polymers. [6] In the case of propene polymerization, one can easily imagine that, within bimetallic-based catalysts, proximity effects between two propagating centers might also be capable of influencing the stereochemical course of alkene insertion into the metal-carbon bond of the pendant polymer chain and, thereby, provide new PP microstructures that are not achievable with the corresponding mononuclear system.…”

“…Unfortunately, results obtained to date with such systems have been far less encouraging, and more specifically, to the best of our knowledge, only one bimetallic species has ever been reported that is catalytically active for the production of PP beyond formation of oligomeric or low molecular weight products. [7,8] However, neither the existence of proximity effects nor their possible influence on PP stereochemical microstructure were mentioned or examined for this systems. [8] For our part, we recently discovered, and then developed, stereomodulated degenerative transfer living (SDTL) Ziegler-Natta polymerization as a means by which to design and prepare, with an unprecedented level of control: (1) an unlimited variety of new polyolefin materials and, in particular, PP microstructural forms -including those possessing an architecturally diverse range of well-defined and discrete isotacticatactic stereoblock and stereogradient profiles and (2), an infinite range of new PP materials based on the programmed introduction of various levels and patterns of mmrm pentad stereoerrors.…”

“…[7,8] However, neither the existence of proximity effects nor their possible influence on PP stereochemical microstructure were mentioned or examined for this systems. [8] For our part, we recently discovered, and then developed, stereomodulated degenerative transfer living (SDTL) Ziegler-Natta polymerization as a means by which to design and prepare, with an unprecedented level of control: (1) an unlimited variety of new polyolefin materials and, in particular, PP microstructural forms -including those possessing an architecturally diverse range of well-defined and discrete isotacticatactic stereoblock and stereogradient profiles and (2), an infinite range of new PP materials based on the programmed introduction of various levels and patterns of mmrm pentad stereoerrors. [3] Importantly, given the living nature of this polymerization process, all these new polyolefin and PP-based materials can be obtained with a pre-selected number-average degree of polymerization, C n , and with a very narrow molecular weight polydispersity index, D = M w /M n % 1.1-1.2.…”