A series of unsymmetrical 2,6-bis(imino)pyridylcobalt(II) complexes, {2-[2,6-(CH(C(6)H(5))(2))(2)-4-Me-C(6)H(2)N==C(CH(3))]-6-(2,6-R(1)(2)-4-R(2)-C(6)H(2)N==CCH(3))-C(5)H(3)NCoCl(2)} where R(1) = Me, Et or (i)Pr, R(2) = H or Me, together with the new symmetrical complex 2,6-[2,6-(CH(C(6)H(5))(2))(2)-4-Me-C(6)H(2)N==C(CH(3))](2)-C(5)H(3)NCoCl(2), were synthesized. All of the compounds were fully characterized by (1)H NMR and IR spectroscopy, as well as by elemental analysis. The molecular structures of Co1 (R(1) = Me, R(2) = H) and Co5 (R(1) = Et, R(2) = Me) were further confirmed by single crystal X-ray diffraction, which indicated that the cobalt centres were penta-coordinate with a pseudo square-pyramidal geometry. Upon treatment with MAO or MMAO, these cobalt pre-catalysts exhibited higher activities than any previously reported cobalt pre-catalysts, with values as high as 4.64 × 10(6) g PE mol(-1)(Co) h(-1) for ethylene polymerization at atmospheric pressure. The polyethylenes obtained were of high molecular weight and narrow molecular weight distribution.
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