Effect of trimethylaluminum on the formation of active sites of the catalytic system bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinato]titanium(IV) dichloride—MAO and catalytic isomerization of hex-1-ene

Abstract

The transformations of bis[N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinato]-titanium(iv) dichloride (L₂TiCl₂) occurring in toluene under the action of methylalumoxane (MAO) were studied by ¹H NMR spectroscopy. The commercially available MAO containing trimethylaluminum (AlMe₃) and MAO free of AlMe₃ (the so called “dry” MAO) were used. The catalytic transformations of hex-1-ene involving the systems L₂TiCl₂-MAO were studied. We proposed the structures of the cationic titanium complexes formed in the absence and in the presence of hex-1-ene under the action of MAO. In the absence of olefin, neutral and cationic titanium complexes are decomposed under the action of AlMe₃ according to the exchange reaction of the complex ligand with the methyl groups of AlMe₃ to form LAlMe₂. The neutral complexes react considerably faster than the cationic ones. In the presence of olefin, decomposition of complexes under the action of AlMe₃ is suppressed. The titanium complex activated by “dry” MAO isomerizes hex-1-ene to hex-2-ene. In the presence of large amounts of TMA (commercial MAO), this reaction does not take place.