Abstract
New ligand platforms of the type p- or m-Ph{-CR(3,6-tBu2Flu)(Cp)}2 (para-, R = Me (2a), H (2b); meta-, R = Me (2c)) were synthesized via nucleophilic addition of the 3,6-tBu2-fluorenyl-anion onto the parent phenylene-bridged difulvenes (1a–c). The corresponding discrete homodinuclear zirconium and hafnium bis(dichloro ansa-metallocene) complexes, Ph[{-CR(3,6-tBu2Flu)(Cp)}MCl2]2 (p-, R = Me (3a-Zr2, 3a-Hf2), R = H (3b-Zr2); m-, R = Me (3c-Zr2), were prepared by salt metathesis reactions. An attempt to generate in situ a heterodinuclear complex 3a-Zr-Hf was also undertaken. For the first time, Atmospheric Pressure PhotoIonization (APPI) mass-spectrometric data were obtained for all dinuclear compounds and found to be in excellent agreement with the simulated ones. Preliminary studies on the catalytic performances of these dinuclear complexes, upon activation with MAO, in ethylene homopolymerization and ethylene/1-hexene copolymerization revealed a few differences as compared to those of the monometallic analogues. In particular, slightly lower molecular weights and a greater formation of short methyl and ethyl branches were obtained with the dinuclear systems.
Highlights
The development and applications of multinuclear group 4 metal α-olefin polymerization catalysts have increased dramatically in the past decade [1,2]
The synthesis of original bis(Cp/Flu) ligand systems linked at the C1-bridge through a phenylene group was developed starting from difulvene precursors
These ligand platforms were utilized for the preparation of homodinuclear zirconium and hafnium bis(dichloro ansa-metallocene) complexes via a regular salt-metathesis metallation protocol
Summary
The development and applications of multinuclear group 4 metal α-olefin polymerization catalysts have increased dramatically in the past decade [1,2]. The interest in this area has primarily been driven by the potential to exploit intermetallic cooperativity/synergism between the two or more proximal metal centers to eventually enhance the performance of polymerization systems. Hold a unique position in α-olefin polymerization thanks to their high activity, excellent control, and remarkable stereospecificity [21,22,23,24,25,26,27,28,29,30,31,32,33]. Only a few dinuclear of systems of this type have been reported in the literature
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