Synthesis, Structure, and Polymerization Activity of [PN]2M(amido)2 (M = Ti and Zr) Complexes

Abstract

The reactions of two equivalents of monoanionic bidentate [PN]-type ligand characterized by a dibenzophosphole-backbone with M (NR₂)₄ (M = Ti, R = Me; M = Zr, R = Et) afforded titanium and zirconium complexes. Two signals appeared in the solution, as evidenced by the presence of a minimum of two diastereomers in the corresponding ³¹P NMR spectrum. The X-ray crystallographic studies of the molecular structures of one of the two diastereomers complexes revealed distorted octahedral structures with phosphorus atoms coordinated to titanium and zirconium centers and the pyrrolido group coordinated to the metal center in the η¹-coordination, and the two dibenzophosphole rings exhibited π-π stacking interactions. Ethylene polymerization at 0.4 MPa using these complexes with dried modified methylaluminoxane (dMMAO) as a cocatalyst produced linear polyethylene (PE) with a melting point of 128°C–136°C. The polymerization activity for ethylene attained values of up to 276 kg/mol (Ti)·h and 223 kg/mol (Zr)·h at 50°C.