Dinuclear Group 4 Metal Complexes Bearing Anthracene-Bridged Bifunctional Amido-Ether Ligands: Remarkable Metal Effect and Cooperativity toward Ethylene/1-Octene Copolymerization.

Two types of bifunctional amido-ether ligands ( syn -L and anti -L ) with the rigid anthracene skeleton were designed to support dinuclear group 4 metal complexes. All organic ligands and organometallic complexes ( syn -M 2 and anti -M 2 ; M = Hf, Zr, and Ti) were fully characterized by 1 H and 13 C NMR spectroscopies and elemental analyses. The anti -Hf 2 complex showed two confirmations at room temperature with C 2 -symmetry or S 2 -symmetry that can inter-exchange, as indicated by VT NMR, while only a C 2 -symmetric isomer was observed for syn -Hf 2 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 syn -Hf 2 , anti -Hf 2 , and syn -Ti 2 in the solid state were further determined by single-crystal X-ray diffraction, revealing the distances between two metal centers in syn -M 2 from 7.138 Å ( syn -Ti 2 ) to 7.321 Å ( syn -Hf 2 ) but a much farther separation in anti -M 2 (8.807 Å in C 2 -symmetric anti -Hf 2 ). The mononuclear complex (2-CH 3 O-C 6 H 4 -N-C 14 H 9 )Zr(NMe 2 ) 3 ( mono -Zr 1 ) was also prepared for control experiments. In the presence of alkyl aluminum (AlEt 3 ) as the alkylating agent and trityl borate ([Ph 3 C][B(C 6 F 5 ) 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 syn -Zr 2 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 syn -Hf 2 and syn -Ti 2 , respectively. Benefitting from both steric proximity and electronical interaction of two metal centers, syn -Zr 2 exhibited significant cooperativity in comparison to anti -Zr 2 and mono -Zr 1 , with regard to activity and molecular weight and 1-octene incorporation of resultant copolymers.