Asymmetric Bis(formamidinate) Group 4 Complexes: Synthesis, Structure and Their Reactivity in the Polymerization of α‑Olefins.

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.