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The influence of the ligand structures of hafnocene polymerization catalysts on ethene insertion and chain propagation was systematically studied by quantum chemical methods. Altogether 54 hafnocenes were studied as a function of the ligand structures. Two consecutive ethene insertions and chain propagations were performed for the catalysts, giving rise to 15 intermediate structures along the reaction pathway. The behavior of the catalysts was analyzed as a function of ancillary ligands, ligand substituents, and bridging units. The differences along the reaction pathway are dominated by the changes in relative stabilities of the catalytic intermediate products. Large aromatic ancillary ligands and electron-donating ligand substituents strongly stabilize the catalyst cations. Steric effects introduced by the ligand framework mostly affect the feasibility of ethene π-coordination and the activation energy for chain propagation. The dominant effect of the relative stabilities of the catalyst intermediates sheds light on the catalytic performance of metallocenes, which may turn out to be useful in further catalyst development.

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Six (Cp)(4‐phenyl‐indenyl)MCl2 (A) and four (Cp)(1‐phenyl‐indenyl)MCl2 (C) (M = Zr/Hf) based complexes were tested in ethene homo‐ and copolymerisation under different conditions to explain how the differences in the complex structure affect the polymerisation process and the formed polymer. Polymerisation experiments reveal that hafnocene catalysts need a higher amount of MAO to reach the maximum activity than zirconocenes. Hafnocenes also incorporate better 1‐hexene. Catalysts with the Cp* or 1,2,4‐Me3Cp ligand show higher activity, and work well with [HNMe2Ph][B(C6F5)4]/TIBA as cocatalyst, but produce polymers with lower $\overline M _{\rm n} $ than the corresponding catalyst with a plain Cp ligand. The Cp* ligand seems to prevent 1‐hexene incorporation. A methyl group in the 2‐position of (Cp)(4‐PhInd)ZrCl2 decreases the activity and $\overline M _{\rm n} $ but favours 1‐hexene insertion. Polymerisation activity is higher with catalysts with a 1‐PhInd‐ligand than with a 4‐PhInd‐ligand.magnified image

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The title compound, [Hf(C22H20Si)Cl2], was solved by simulated annealing from laboratory X‐ray powder diffraction data collected at room temperature. The mol­ecular structure comprises a hafnium dichloride centre, coordinated by a η5‐cyclo­penta­dienyl and a η5‐3‐phenyl­indenyl unit, which are connected through a shared dimethyl­silicon linkage.