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In order to study the influence of substituents on imino-aryl rings of mono(imino)pyrrole-transition metal complexes to their ethylene polymerization performance,a series of mono(imine)pyrroles (L1-L3) were synthesized by microwave irradiation from 2-acetylpyrrole and a series of 2,6-position disubstituted anilines (substituent:H,Me,Et).A simplified synthetic method was introduced to prepare the corresponding nickel complexes NiL2 (1 ～3) with direct condensation of mono(imine)pyrrole ligands and nickel dichloride.All the compounds were fully characterized by 1H NMR,IR,EA,MS,and X-ray crystal diffraction.Ligand L3 (C16H20N2,Mr =240.34) belongs to the triclinic system,space group P(ī),with a =7.9606(19),b =9.028(2),c =11.205(3) (A),the final R =0.0606 and wR =0.1875.Complex 3 (C32H38N4Ni,Mr =537.37) belongs to the monoclinic system,space group C2/c with a =19.811 (3),b =11.262(2),c =26.004(4) (A),the final R =0.0388 and wR =0.1020.The crystal structures indicated that all the Nin complexes have similar tetra-coordinated geometries,in which the ligand chelated to the center nickel with a 2:1 molar ratio.Catalytic properties of the Nin complexes for ethylene polymerization were systematically investigated,and the results showed a regular increase of catalytic activities with steric hindrance of the substituents on the imino-aryl ring of NiⅡ complexes.