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 I, 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 degrees 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 degrees 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 degrees 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. (C) 2015 Elsevier B.V. All rights reserved.