A series of asymmetric formamidine ligands bearing different substituents with various steric and electronic properties on the nitrogen of the N–C–N motif were synthesized. Group 4 bis(formamidinate) dimethylamido, chloride, and benzyl complexes were studied using these asymmetric ligands and their solid-state structures and their behavior in solution were determined. These complexes were activated with MAO (methylalumoxane) or a combination of cocatalysts and tested in the polymerization of ethylene and propylene. A noticeable influence of the formamidine nitrogen substituents on the activity of the catalyst and properties of the obtained polymers was observed. Further, a plausible mechanism for the polymerization of propylene is presented derived from a combination of ESR-C60 and MALDI-TOF trapping experiments which shed light on the nature of the active catalytic species.
Dr. Naveen V. Kulkarni, Elkin, T., Tumaniskii, B., Botoshansky, M., Shimon, L. J. W., and Eisen, M. S., “Group 4 Complexes: Synthesis, Structure and Their Reactivity in the Polymerization of α-Olefins.”, ACS Regional Meeting , vol. 33. University of Texas Arlington, TX, United States, pp. 3119-3136, 2014.