Synthesis Of Bis-(β-ketoiminato) Ni(Ⅱ) With C-C Bridged CGC And Their Catalytic Copolymerization For Norbornene

Vinyl-addition type polynorbornene（PNB） was an attractive material due to its unique characteristics, such as low refractive index, high transparency, excellent chemical resistance. On the other hand, its processability such as poor solubility and adhesion could be improved by copolymerizing with polar norbornene derivatives and introducing the polar group. A novel, effectual, stable, single-site catalyst was the key to realize the copolymerization and obtained the copolymers with high molecular weight as well as narrow distribution.Series of β-ketoimine ligands（L1-L5） were synthesized by the reaction of β-diketone and 9-fluorene or benzylamine bearing active C-H bond. L1:CF₃C（O）CHC[HN（fluorenyl）]Ph,L2-L5:R₁C（O）CHC[HN（benzyl）]R₂（L2:R₁=CH₃,R₂=CH₃;L3:R₁=Ph,R₂=CH₃;L4:R₁=CF₃,R₂=CH₃;L5:R₁=Ph,R₂=Ph）。And the structures of the β-ketoimine ligands（L3-L5） have been confirmed by single crystal X-ray diffractions. Furthermore, the bis-（β-ketoiminato） Ni（Ⅱ） complexes with C-C bridged CGC were synthesized by the coordination reaction and one-step in situ coupling reaction in the presence of（DME） NiBr₂, C1 :{CF₃C（O）CHC[ N（fluorenyl）]Ph}₂ Ni, C2-C5 :{R₁C（O）CHC[N（benzyl）]R₂}₂Ni（C2:R₁=CH₃,R₂=CH₃;C3:R₁=Ph,R₂=CH₃;C4:R₁=CF₃,R₂=CH₃;C5:R₁=Ph,R₂=Ph）. The active C-H bond in the β-ketoimine ligands could be activated by（DME）NiBr₂ and forming the coupling C-C bond while the ligands coordinated with the metal centers. The structure of the complex C1 have been confirmed by single crystal X-ray diffractions with C-C bridged constrained geometry configuration（CGC）.The bis-（β-ketoiminato） Ni（Ⅱ） complexes with C-C bridged CGC were applied to the homopolymerization of NB and copolymerization of NB and NB-COOCH₃ combined with B（C₆F₅）₃ in toluene. The results showed that the catalytic systems exhibited high activities（as high as 106 gpolymer/molNi·h） when applied to the homopolymerization of NB. Furthermore, C2-C5 were applied to the copolymerization of NB and NB-COOCH₃, the obtained addition-type copolymersexhibited relatively high molecular weights（5.03×104-8.9×104g/mol） and narrow molecular weight distribution（1.01-1.05）. The results showed that the activity of bis-（β-ketoiminato） Ni（Ⅱ） complex C4 bearing the electron-withdrawing substituent CF₃ achieved the highest activity（3.39×105 gpolymer/molNi·h）. Besides, all the copolymers exhibited good thermal stability（Td>400 oC） as well as high transparency（T>85%） and could be dissolved in chlorobenzene at room temperature.