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Summary: Propene polymerisation was conducted with three ansa‐zirconocene complexed: Me2Si(2‐Me‐4‐PhInd)2ZrCl2 (A), Me2Si(2‐Me‐4‐PhInd)2ZrClNMe2 (B) and Me2Si(2‐Me‐4‐PhInd)2ZrClNEt2 (C). Methylalumoxane (MAO) or [HNPhMe2][B(C6F5)4] was used as cocatalyst. The influence of cocatalysts and triisobutylaluminum (TIBA) on polymerisation activity, molecular weight and polymer microstructure was studied. Furthermore, the alkylation and activation of the complexes were examined using UV/VIS spectroscopy. Complex A was the most active in polymerisation, but polymers produced by B and C had in general higher molecular weights. Replacing MAO partially by TIBA increased the molecular weight and prevented catalyst deactivation. According to the UV/VIS measurements, all complexes have low reactivity towards TMA and TIBA. Similar cationic species were formed of all three studied zirconocenes in the reaction with MAO. Additional TIBA did not affect the type of active species formed in the reaction of zirconocene and MAO, but increased the activity of B and C.UV/VIS spectrum of complex A with MAO and with a MAO/TIBA mixture.imageUV/VIS spectrum of complex A with MAO and with a MAO/TIBA mixture.

Among the 2-substituted indenes, 2-trifluoroindene and 2-tert-butylindene are poorly or incompletely described in the open literature. We herein describe an efficient one-pot synthesis of these compounds as a variation of the Perkin reaction which allows us to refute an earlier claim that bis(2-tert-butylindenyl)zirconium(IV) dichloride (2a) will not polymerise ethene. In fact, 2a/MAO polymerises ethene to extremely high molecular weights. Extensive DFT calculations on the polymerisation mechanism revealed an unprecedented suppression of the otherwise predominant chain termination by beta-hydride transfer due to steric congestion of the active site.

Summary: Propene‐ethene copolymers with low to moderate amounts of ethene were synthesised with two Cs‐symmetric metallocene complexes, [(p‐CH3OPh)2C(2,7‐di‐tBuFlu)(Cp)]ZrCl2 (I) and [(p‐CH3OPh)2C(2,7‐di‐tBuFlu)(Cp)]HfCl2 (Ia). Methylalumoxane (MAO), N,N‐dimethylanilinium tetra(pentafluorophenyl)borate {[Me2HNPh][B(C6F5)4]}, trityl tetra(pentafluorophenyl)borate {[Ph3C][B(C6F5)4]} and tris(pentafluorophenyl)borane [B(C6F5)3] were used as cocatalysts in the polymerisations. The differences in polymerisation activity, ethene incorporation rate and molecular weight as well as the microstructure and the thermal behaviour of the homo‐ and copolymers were studied.The different cocatalysts have a strong influence on the polymerisation activity and the syndiotacticity of the polymers, but only a minor influence on the ethene incorporation rate and the molecular weight. At 30 °C, the incorporation rate of ethene is ca. 25 times faster for complex I and ca. 16 times faster for complex Ia than the incorporation rate of propene. The thermal behaviour of the homo‐ and copolymers is dependent of the polymerisation temperature and the cocatalyst. I/MAO produces homo‐ and copolymers at 30 °C with more regular microstructure than I/[Me2HNPh][B(C6F5)4], I/[Ph3C][B(C6F5)4] and I/B(C6F5)3 leading to homo‐ and copolymers with higher melting and crystallisation temperatures. On the contrary, at 0 °C I/[Me2HNPh][B(C6F5)4] and I/[Ph3C][B(C6F5)4] produce copolymers with higher propene sequence syndiotacticity and higher melting and crystallisation temperatures than I/MAO. The influence of the cocatalyst on the catalyst coordination environment is temperature‐dependent and thereby the structure of the forming homo‐ or copolymers varies.Effect of different cocatalysts and the amount of ethene in the feed on the polymerisation activity of complex I.magnified imageEffect of different cocatalysts and the amount of ethene in the feed on the polymerisation activity of complex I.

The systematic synthesis of 1,3-dialkyl-substituted 2-silylindenes and their suitability as zirconocene ligands is discussed. Unexpected reactivities rendered a number of substitution patterns unfeasible, especially for alkyl groups other than methyl in 2-(trimethylsilyl)indene derivatives, and essentially for all derivatives of 2-(dimethylsilyl)indene. The syntheses of rac/meso-bis [1-methyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (12) and bis [1,3-dimethyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (13b) are de- IntroductionThe field of metallocene-catalyzed olefin polymerization has achieved significant improvements on polymer properties. The ligandϪtacticity relationship is well understood and, apart from tailor-made stereocontrol, co-monomer incorporation and block length have been emphasized as keys to innovative materials.[1] The detailed polymerization mechanism with all its variations is complicated and the choice of appropriate polymerization conditions to favor one monomer over the other still requires vast and tedious sets of experiments. An outline of the extensive efforts made within this area can be found in the various review articles. [2] Previous work from our laboratory addressed unbridged zirconocene dichloride with silyl substituents in the 1 or 2 position.[3] Reports on trisubstituted indenyl ligands, i.e. substituents in the 1, 2, and 3 positions, are still quite uncommon. It may be expected that steric congestion in such complexes is significant and that overall polymerization activity may be negatively influenced. In this study, we wish to present our results on a systematic study of 1,3-dialkyl-2-silyl-trisubstituted indene ligands for the synthesis of zirconocene dichlorides. Results and Discussion Ligand SynthesesThe introduction of alkyl groups in the 1 and 3 position of 2-silylindenes should be feasible in a straight forward manner by simple double alkylation of indenyllithium salts. Deprotonation of 2-(dimethylsilyl)indene (1a, 2-DMS-Ind) and 2-(trimethylsilyl)indene (1b, 2-TMS-Ind) was achieved by n-butyllithium in pentane at room temperature or -90°C, respectively. In spite of the nonpolar solvent, deprotonation at lower temperatures provided hydride substitution products for 1a, as observed by Kira et al.[4] Alternatively deprotonation can be achieved with potassium hydride at room temperature.Methylation of the lithium salt of 1a with methyl iodide at -40°C in diethyl ether yielded exclusively 3-Me-2-DMSInd (2a), while 1-Me-2-TMS-Ind (2b) was obtained likewise from 2-TMS-Ind. Repetition of the deprotonationϪmethyl-ation sequence afforded a 1:4 mixture of the 1,1-dimethyl and 1,3-dimethyl isomers for both, 3a and 3b. Deprotonation and washing with pentane provided pure lithium salts of the 1,3-dimethyl-2-silylindenes 3a and 3b (Scheme 1). 3a exhibits diastereotopic methyl resonances of the silyl group in a 1:1 ratio due to the presence of the chiral C(1) atom.In order to determine whether bulkier alkyl substituents could be placed in the 1,3 positions, studies ...