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Abstract

The C₆H₆.Ti(II)(AlBr₄)₂ (Ib) catalyst deactivates during the butadiene cyclotrimerization to give a solid containing all titanium (mostly as TiBr₃) and a mixture of AlBr₃ and RAlBr₂ compounds dissolved in benzene. The residual cationic catalytic activity of the deactivated Ib system is due to presence of AlBr₃. In contrast to TiCl₃, the deactivated Ib system and the model system TiBr₃ + AlBr₃ are not activated by the addition of EtAlCl₂ in the presence of butadiene: the highly active benzenetitanium(II) system is re-constituted only after reduction of TiBr₃ with Et₃Al followed by the addition of EtAlCl₂. The addition of Et₂AlBr to Ib accelerates the deactivation of the system. Deactivation products of this system contain mainly Ti(II) species which forms benzenetitanium(II) catalytic system after addition of EtAlCl₂. All the EtAlCl₂ reactivated systems produce (Z, E, E)-1,5,9-cyclododecatriene with high catalytic stability and considerable selectivity (>90%). This behaviour points to the catalysis by benzenetitanium(II) chloroalane complexes containing only low amount of bromine atoms and ethyl groups.