Synthesis of well defined C–C bridged Ni(ii) complexes bearing β-ketoiminato-fluorene ligands by bifluorenyl in situ coupling and application for norbornene (co)polymerization

Abstract

Well defined 9-substituted fluorene C–C bridged constrained geometry configuration (CGC) Ni(II) complexes bearing β-ketoiminato-fluorene ligands, {CH₃C(O)CHC[N(fluorenyl)]-CH₃}₂Ni (Ni1) and {CF₃C(O)CHC[N(fluorenyl)]-CH₃}₂Ni (Ni2) were synthesized by coordination reaction and in situ coupling reaction in the presence of (DME)NiBr₂. The complexes were characterized by NMR and elemental analyses. And the quality Ni1 and Ni2 crystals structure was confirmed from X-ray with C–C bridged constrained geometry configuration. On activation with B(C₆F₅)₃, the Ni-based complexes showed high catalytic activities for norbornene homo-polymerization, activities up to 10⁶ g PNB mol per Ni per h. The copolymerization of 2-heptoxymethylene norbornene (HN) with norbornene by the pre-catalysts Ni1 and Ni2 was also explored in the presence of B(C₆F₅)₃. High molecular weight polymers with unimodal molecular weight distributions were obtained, indicating that the nature of the polymerization was single site. The catalytic activity, co-monomer incorporation and the properties of the resultant polymers can be controlled over a wide range by tuning the catalyst structures and reaction parameters.