Methylenebis(indenyl)zirconium dichloride substituted in C(3), activated by methylalu- moxane, is able to give polystyrene and ethylene-styrene copolymers. In this study hydrooligomers, whose structure, determined by 13C NMR and GC-MS techniques, gives information about the regiochemistry and the stereochemistry of styrene insertion, have been purposefully prepared. The regiochemistry of the styrene insertion is related to the encumbrance of substituents in C(3). rac-[Methylene- (3-R-1-indenyl)2]ZrCl2 with R ) H, CH3, or CH2CH3 induces a prevailingly secondary styrene insertion into the zirconium-carbon bond. With increasing the substituent’s steric hindrance (R ) CH(CH3)2), regiochemistry inversion occurs and the primary insertion becomes prevailing. The analysis of ethylene- styrene copolymers obtained in the presence of the different catalysts allows confirming the correlation between regiochemistry and comonomers’ reactivity. Besides, also the stereospecificity can be evaluated from the structure of the hydrotrimers, when the insertion is primary. Whereas the isospecificity in the absence of substituents (secondary insertion) and in the presence of the tert-butyl substituent (primary insertion) is well-known, a surprising syndiospecificity is observed when the indenyl ligand bears the isopropyl substituent in C(3).

Regiochemistry of the Styrene Insertion with CH2-Bridged ansa Zirconocene-Based Catalysts

IZZO, Lorella;OLIVA, Leone
2003

Abstract

Methylenebis(indenyl)zirconium dichloride substituted in C(3), activated by methylalu- moxane, is able to give polystyrene and ethylene-styrene copolymers. In this study hydrooligomers, whose structure, determined by 13C NMR and GC-MS techniques, gives information about the regiochemistry and the stereochemistry of styrene insertion, have been purposefully prepared. The regiochemistry of the styrene insertion is related to the encumbrance of substituents in C(3). rac-[Methylene- (3-R-1-indenyl)2]ZrCl2 with R ) H, CH3, or CH2CH3 induces a prevailingly secondary styrene insertion into the zirconium-carbon bond. With increasing the substituent’s steric hindrance (R ) CH(CH3)2), regiochemistry inversion occurs and the primary insertion becomes prevailing. The analysis of ethylene- styrene copolymers obtained in the presence of the different catalysts allows confirming the correlation between regiochemistry and comonomers’ reactivity. Besides, also the stereospecificity can be evaluated from the structure of the hydrotrimers, when the insertion is primary. Whereas the isospecificity in the absence of substituents (secondary insertion) and in the presence of the tert-butyl substituent (primary insertion) is well-known, a surprising syndiospecificity is observed when the indenyl ligand bears the isopropyl substituent in C(3).
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/1060864
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