Metal (Mg, Fe, Co, Zr and Ti) complexes derived from aminosilyl substituted aminopyridinato ligand: Synthesis, structures and ethylene polymerization behaviors of the group 4 complexes

摘要

Lithium N-[(N,N-dimethylamino)dimethylsilyl]-2-pyridylamidate (2) was prepared from the reaction of new compound N-[(N,N-dimethylamino)dimethylsilyl]- 2-pyridylamine (1) and LiBu n. Treatment of the lithium salt (2) with an equal equivalent of MgBr _2(THF) _2, FeCl _2 and CoCl _2 afforded the corresponding dinuclear complexes 3, 4, and 5, in which metal atoms possess similar trigonal bipyramidal geometries and each ligand functions as a bimetallic bridging binding aminopyridinato moiety with N-donation from the dimethylamino group. While the stoichiometric reaction of 2 with ZrCl _4 gave the mononuclear zirconium complex (6); the seven coordinated zirconium atom adopts a distorted pentagonal bipyramid geometry and the ligand acts as monoanionic η ~2-aminopyridinato moiety with the pendant arm coordinated via N(CH _3) _2. The reaction of 2 with one equivalent of TiCl _4(THF) _2 produced the interesting dinuclear titanium complex (7) owing to the elimination of a (N,N-dimethylamino)dimethylsilyl group from the original ligand, and the two titanium centers present different coordination geometries. The molecular structures of the crystalline metal complexes 3-7 have been confirmed by X-ray single crystal diffraction analysis. Upon activation with methylaluminoxane (MAO), both complexes 6 and 7 exhibited moderate catalytic activities toward ethylene polymerization and produced high molecular weight polyethylenes with broad molecular weight distributions.