New air stable cationic methallyl Ni complexes bearing imidoyl-indazole carboxylate ligand: Synthesis, characterization and their reactivity towards ethylene

• Design and synthesis of three neutral N,N imidoyl-indazole methoxycarbonyl ligands.
• Synthesis and characterization of air-stable [(methallyl)Ni(N,N)]B(Ar’)4 complexes.
• Study of ethylene polymerization with Ni-complexes and B(C6F5)3.
• Polymerization products strongly depended of the complex and reaction conditions.

Three new neutral N,N imidoyl-indazole ligands with a methoxycarbonyl functional group (1–3) and three new air-stable cationic methallyl nickel complexes (4–6) were prepared. These compounds were characterized by NMR, FT-IR and elemental analyses. In addition, compounds 1, 2, 3 and 4 were analyzed using X-ray diffraction. An evaluation of the reactivity of complexes 4–6 toward ethylene was conducted by using 5 equivalents of B(C6F5)3. At 1 bar of ethylene and 20 °C, only complexes 4 and 6 were able to produce butene, showing unusual air stability and dimerizing ethylene even after exposure to air for 48 h. By increasing the pressure to 12 bar at 20 °C, complex 6 showed a catalytic activity of 401 Kg product (mol Ni)−1 h−1, producing a low molecular weight polyethylene (26.6 Kg/mol) with almost exclusively methyl branches (2.3 mol%). By increasing the temperature to 60 °C at 12 bar of ethylene, the system 6/B(C6F5)3 increased its catalytic activity to 487 Kg product (mol Ni−1) h−1, but produced a significant decrease in the molecular weight of the polymer (1.8 Kg/mol) and a broad distribution of branches.

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