Influence of the Substituents on Imino-aryl Ring of Mono(imino)pyrrole-Ni~(Ⅱ) Complexes to Their Ethylene Polymerization Catalytic Performance

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 NiL_2(1～3) with direct condensation of mono(imine)pyrrole ligands and nickel dichloride. All the compounds were fully characterized by 1 H NMR, IR, EA, MS, and X-ray crystal diffraction. Ligand L3(C_(16)H_(20)N_2, Mr = 240.34) belongs to the triclinic system, space group P1, with a = 7.9606(19), b = 9.028(2), c = 11.205(3) ?, the final R = 0.0606 and wR = 0.1875. Complex 3(C_(32)H_(38)N_4Ni, 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) ?, the final R = 0.0388 and wR = 0.1020. The crystal structures indicated that all the Ni~(Ⅱ) 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 Ni~(Ⅱ) 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 Ni~(Ⅱ) complexes.

Influence of the Substituents on Imino-aryl Ring of Mono(imino)pyrrole-NiⅡ Complexes to Their Ethylene Polymerization Catalytic Performance