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| - Reactivity of the [(η5-C5Me5)TiCH3][RB(C6F5)3] Complexes Identified asActive Species in Syndiospecific Styrene Polymerization
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| - The reactivity of the alkyl complexes [Cp*Ti(III)(CH3)][RB(C6F5)3] (Cp* = η5-C5Me5; R =CH3, −C6F5) with α-13C-enriched p-chlorostyrene has been investigated by means of ESR spectroscopy inorder to gain insight into the chemical structure of the active species in syndiospecific polymerization ofstyrene and substituted styrenes promoted by “half-titanocene”-based catalysts. Secondary (2,1)polyinsertion of p-chlorostyrene into a Ti(III)−alkyl bond has been observed under polymerizationconditions. The role of Cp*TiIIIR+ complexes in syndiospecific styrene polymerization has conclusivelybeen confirmed. Furthermore, the reaction of the 13C-enriched complex [Cp*Ti(13CH3)][RB(C6F5)3] withPMe3 and Al(13CH3)3 has also been investigated by ESR spectroscopy. PMe3 displaces the methylborateanion from the coordination sphere of the Cp*Ti13CH3(μ-13CH3)B(C6F5)3 ion pair and produces thecorresponding phosphine adduct Cp*Ti(CH3)(PMe3)2+. In the same manner, the reaction of [Cp*Ti(13CH3)][B(C6F5)4] with Al(13CH3)3 affords the [Cp*Ti(μ-13CH3)3Al(13CH3)]+ adduct. The increase of theintensity of the Ti(III) signals observed in the ESR spectra of these catalytic systems after addition ofthe monomer has been explained on the basis of the ESR results reported above.
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