Activation effect of metal chlorides in post-metallocene catalytic systems for ethylene polymerization: A DFT study

• The activation effect of metal chlorides in ethylene polymerization was studied.
• The reactions between LTi(Y)Cl (Y = Me, Cl) and metal chlorides were considered.
• The complexes LTi(Y)Cl⋅nMgCl2 (n = 1, 2) and LTi(Y)Cl⋅MgCl2⋅AlMe2Cl can be formed.
• Secondary complexation reactions significantly enhance the catalytic activity.
• The catalytic sites in ethylene polymerization have the non-ionic nature.

This work is devoted to the DFT study of the activation effect of metal chlorides (MgCl2, LiCl, ZnCl2, CaCl2) in ethylene polymerization reactions on post-titanocene complexes LTi(Y)Cl (1), where L is the bidentate saligenin type ligand, Y is alkyl group or Cl. The activation effect of metal chlorides is caused by secondary complexation reactions between 1 and metal chlorides. In accordance with previously reported experimental data, our DFT calculations predict that the most probable catalytic particles in the systems based on MgCl2 possess higher reactivity with respect to ethylene molecule than in the systems based on LiCl. One could expect a higher catalytic activity for CaCl2 than for MgCl2, but for ZnCl2 the catalytic activity should be the lowest. Results of our calculations show that at least three different hetero-trinuclear compounds of Ti, Mg and Al have similar reactivity towards ethylene molecule. This result explains Mw/Mn indexes >2 measured earlier for one of the systems under the study with R3Al (R = Me, t-Bu) as activators.

The activation effect of metal chlorides in ethylene polymerization is caused by secondary complexation reactions of chlorides with post-titanocene complexes. The calculated structures of the transition states of C–C bond formation step of the reactions of ethylene molecule with two most stable compounds of the composition LTi(Me)Cl·2MgCl2 are shown.Figure optionsDownload as PowerPoint slide