Structural flexibility of bis(phenoxyimine) titanium complexes in the early stages of olefin polymerization process: a DFT study

The behaviors of three structurally similar salan- and phenoxyimine-based catalysts activated by perfluorophenylborate were compared in the early stages of ethylene polymerization. It was found that moderate modification of the ligand structure can dramatically reduce the interactions between the cationic active site and the counteranion and, as a result, decrease the theoretically calculated upper bound to the ion separation barrier from 15 to 2 kcal/mol. The interactions between the ions in the ion pair have further repercussions on the structure of the active sites (octahedral vs square pyramid), transition states and thus the insertion barriers.