Synthesis of New Titanium Complexes Bearing a Bidentate Monoanionic Inversely-Polarized Phosphaalkene-Enolate Ligand and their Activity in Olefin Polymerization

The synthesis and characterization of several inversely-polarized phosphaalkenes, including the first ring-expanded inversely-polarized hydrido-phosphaalkene and imidazolidine-based inversely-polarized phosphaalkene-enolate ligand precursors, are herein reported. Coordination of the imidazolidine-based ligands to titanium was studied. Minimal decomposition (6%) of the isolated complex occurred over several days at 60 C. The titanium complexes were explored computationally where it was revealed that there is evidence for the phosphorus atom of the bound ligand to donate an additional pair of electrons to Ti, resulting in a large stabilization of 18.2 kcal mol1. Furthermore, the titanium complex has activity up to 5.64 kgPE mol1Ti h1 in the polymerization of ethylene with little decomposition of the active species over several hours. The polymer produced was high-density polyethylene with an average molecular weight of 17.6 kDa and a Tm of 131 C.