The influence of alkali metal halides on the butadiene cyclotrimerization catalyzed by (benzene)titanium(II) complexes

Abstract

Addition of alkali chlorides (MCl) to (η6-C6H6)Ti(AlCl4)2 (Ia) decreases the catalytic activity of Ia while the selectivity of the (Z,E,E)-1,5,9-cyclododecatriene formation is improved only when NaCl is used at the optimum molar ratio NaCl/Ia ~ 5. The alkali chlorides remove free AlCl3, which is present in the system as an admixture, probably in the form of MAlCl4 complexes; however, an excess of MCl brings about the decomposition of catalytic trinuclear Ti(II) complexes during the butadiene cyclotrimerization. In addition to inactive TiCl2, this decomposition yields some AlCl3 which induces the formation of cationic byproducts, 1-phenylbut-2-ene and (E)-1,4-poly(butadiene), before it is deactivated or quenched with MCl.