Coplanar binuclear group 4 post-metallocene complexes supported by chelating μ-(σ₂-aryl) ligands : characterisation and olefin polymerisation catalysis

The report concerns expansion of the previously developed M-[O,N,C] [pyridine-2-phenolate-6-(σ-aryl)] catalyst system into rigid, coplanar bimetallic assemblies, which afford metal–metal distances that are predetermined yet amenable for cooperativity, as well as locked-in “syn” orientation of binding sites that offer the same direction of access for substrates. The binuclear complexes are generated in a regioselective manner to yield para hydrogen atoms (not ortho) at the central μ-aryl moiety, and have been characterised by multinuclear NMR spectroscopy. The “anti” (showing opposite directions of access) and mononuclear analogues have also been prepared for comparison purposes. Six syn-type bimetallic derivatives of Ti, Zr and Hf have been characterised by X-ray crystallography, to reveal metal–metal separations of 6.3–6.7 Å. For ethylene and ethylene/1-octene polymerisation reactions in conjunction with trityl borate, the syn-Ti₂ catalysts display superior efficiencies and produced polymers with higher M_w values than for the anti  and mono-Ti congeners, thus indicating the possibility of favourable enchainment interactions and cooperative reactivity.

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