Complexes of transition metals with Lewis bases as precursors of olefin polymerisation catalysts. 2. Progress in computer assisted design of catalysts

摘要

The detailed knowledge and understanding of the mechanisms of polymerisation of olefins in the presence of various catalysts, described in the first part of this series of articles [1], led to intensive searches for catalysts with defined properties, using the method of computer assisted design. In T. Ziegler's group [2] this was undertaken with complexes of metals in group IV of the periodic system with ligands containing a nitrogen atom, which would be capable of catalysing "living" polymerisation of olefins.The work contains an explanation for the activity of complexes of titanium, zirconium and hafnium of the type [HN(CH_2)_3NH]MtC_3H_7~+ in the oligomerisation of ethylene based on the values of the complexing, insertion and #beta#-elimination barriers calculated by DFT methods. Analysis of actual polymerisation catalysts containing large aryl groups, and explanation of the role of these groups as well as the influence of the radius of the transition metal atom on inhibition of the termination process, wasd made possible by QM/MM methods (combining quantum mechanics and molecular mechanics). Guided by the results obtained and the relations observed, the authors proposed a new zirconium catalyst for polymerisation of ethylene.