Synthesis and Structure of Group 4 Symmetric Amidinate Complexes and Their Reactivity in the Polymerization of α‑Olefins

The steric properties of various
nitrogen substituents on amidines
were tuned in order to obtain group 4 mono- and bis­(amidinate) dimethylamido
or chloride complexes. The amidinate dimethylamido and chloride complexes
were prepared, and their solid-state as well as their solution-state
structures were studied. After the activation by MAO, these complexes
were tested in the polymerization of propylene and ethylene. A noticeable
influence of the amidine carbon and nitrogen substituents on the activity
of the catalyst and properties of the obtained polymer was observed.
Further, a plausible mechanism for the ethylene polymerization process
is presented taking into account a combination of ESR-C60 and MALDI-TOF experiments, shedding light on the nature of the catalytic
species.