Synthesis of Titanium Heteroarylphosphinimine Complexes and Application for Ethylene Polymerization

Mono-and bisdiphenyl substituted heteroarylphosphines R-PPh₂[R=2-pyridyl (3a), 2-thienyl (3b) and 2-furyl (3c)] and Ph₂P-R'-PPh₂[R'=2,6-pyridyl (6a), 2,5-thienyl (6b) and 2,5-furyl (6c)] were synthesized. After Staudinger reaction with Me₃SiN₃, those heteroarylphosphines were converted into the heteroarylphosphinimine ligands, R-PPh₂(NSiMe₃) and (Me₃SiN)Ph₂P-R"-PPh₂(NSiMe₃). The subsequently dehalosilylation reaction with CpTiCl₃ afforded the corresponding Ti heteroarylphosphinimine halfmetallocenes as olefin polymerization catalysts. The structures of all the complexes were determined by means of ¹H NMR, ¹³C NMR and ³¹P NMR spectroscopic methods and further confirmed by single-crystal X-ray diffraction analysis. When activated with methylaluminoxane (MAO) at a ratio of Al/Ti=600 and under 0.5 MPa of ethylene, these bimetallic Ti phosphinimine complexes displayed a higher catalytic activity compared to the monometallic analogues, but resulted in polymers with bimodal molecular weight distributions. Unexpectedly, 6b produced ultrahigh M_w polyethylene at lower polymerization temperature.