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

A seriesof asymmetric formamidine ligands bearing different substituents withvarious 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 theseasymmetric ligands and their solid-state structures and their behaviorin solution were determined. These complexes were activated with MAO(methylalumoxane) or a combination of cocatalysts and tested in thepolymerization of ethylene and propylene. A noticeable influence ofthe formamidine nitrogen substituents on the activity of the catalystand properties of the obtained polymers was observed. Further, a plausiblemechanism for the polymerization of propylene is presented derivedfrom a combination of ESR-C60and MALDI-TOF trapping experimentswhich shed light on the nature of the active catalytic species. [ABSTRACT FROM AUTHOR]