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Two 2-Py-amidine ligands (2-Py-NH-C(Ph) N-Ar, Ar = 2,6-Me 2 C 6 H 3 and 2,6-i Pr 2 C 6 H 3 ) and the corresponding Ni(II) complexes (1 and 2) were synthesized and characterized using elemental analysis and FT-IR, UV-visible, 1 H NMR and 13 C NMR spectroscopies. X-ray crystal structures indicate that the chelate ring conformation of the less bulky complex 1 is relatively planar compared with that of the bulky complex 2. Paramagnetic 1 H NMR and 13 C NMR studies show that, in solution, the time-average structures of complexes 1 and 2 have mirror symmetry. Both complexes 1 and 2 were used as catalyst precursors for norbornene polymerization with methylaluminoxane as a co-catalyst. The effects of Al/Ni ratio, temperature and structure of precursors on the catalytic performance were investigated.

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