Synthesis and spectroscopic characterization of titanium pyridylanilido complexes as catalysts for the polymerization of 1,3-butadiene and isoprene

A series of titanium(IV) complexes of general formula TiCl3[N,N-(pyridin-2-ylalkyl)anilido, TiCl3L, 8–13, were prepared by reactions of TiCl4 with substituted (pyridin-2-ylalkyl)anilines, LH, and characterized by analytical and spectroscopic methods. Compound 10 was obtained by using TiI4 as titanium precursor. In the case of LH = 2,6-diisopropyl(pyridin-2-ylmethyl)aniline, 1, and 2,6-diisopropyl(pyridin-2-ylethyl)aniline, 2, the intermediate formation of TiCl4LH, 6–7, was detected, undergoing HCl elimination on heating to finally give 8 and 9. The products are not stable in coordinating solvents (thf, CH3CN). Ligand dissociation was observed from TiCl3(N,N-2,6-diisopropyl(pyridin-2-ylmethyl)anilido, 8, resulting in the formation of Ti2OCl6(CH3CN)4 and 2-(2,6-diisopropyl-phenylaminomethyl)pyridinium hexachlorotitanate. By reaction of TiCl3(thf)3 or TiI3 with 1 and 2 at ca 100 °C, the air sensitive derivatives TiCl2L, 14, and TiI2L, 15, were afforded. All titanium complexes were evaluated as catalysts for the polymerization of 1,3-butadiene and isoprene, in association with methylaluminoxane (MAO). The results indicate that the catalytic activity is strictly dependent on the nature of the ligands and the oxidation state of the metal, while the nature of the titanium complex has negligible influence on the selectivity.