Dinuclear Group 4 Metal Complexes Bearing Anthracene-Bridged Bifunctional Amido-Ether Ligands: Remarkable Metal...

Two types of bifunctional amido-ether ligands ( and ) with the rigid anthracene skeleton were designed to support dinuclear group 4 metal complexes. All organic ligands and organometallic complexes ( and ; M = Hf, Zr, and Ti) were fully characterized by ¹H and ¹³C NMR spectroscopies and elemental analyses. The complex showed two confirmations at room temperature with C₂-symmetry or S₂-symmetry that can inter-exchange, as indicated by VT NMR, while only a C₂-symmetric isomer was observed for complex at room temperature. However, for Zr and Ti analogues, both syn and anti complexes exhibited only one conformation at room temperature. The molecular structures of complexes , , and in the solid state were further determined by single-crystal X-ray diffraction, revealing the distances between two metal centers in from 7.138 Å () to 7.321 Å () but a much farther separation in (8.807 Å in C₂-symmetric ). The mononuclear complex (2-CH₃O-C₆H₄-N-C₁₄H₉)Zr(NMe₂)₃ () was also prepared for control experiments. In the presence of alkyl aluminum (AlEt₃) as the alkylating agent and trityl borate ([Ph₃C][B(C₆F₅)₄]) as the co-catalyst, all metal complexes were tested for copolymerization of ethylene with 1-octene at high temperature (130 °C). The preliminary polymerization results revealed that the activity was highly dependent upon the nature of metal centers, and showed the highest activity of 9600 kg(PE)·mol^-1 (Zr)·h^-1, which was about 17- and 2.2-fold higher than those of and , respectively. Benefitting from both steric proximity and electronical interaction of two metal centers, exhibited significant cooperativity in comparison to and , with regard to activity and molecular weight and 1-octene incorporation of resultant copolymers.