Bimetallic Effects for Enhanced Polar Comonomer Enchainment Selectivity in Catalytic Ethylene Polymerization (2010)

The synthesis and characterization of the bimetallic 2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato\ngroup 10 metal polymerization catalysts {[Ni(CH&lt;sub&gt;3&lt;/sub&gt;)]&lt;sub&gt;2&lt;/sub&gt;[1,8-(O)&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;-2,7-[CH=N(2,6-&lt;sup&gt;i&lt;/sup&gt;Pr&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;)](PMe&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;} and {[Ni(1-naphthyl)]&lt;sub&gt;2&lt;/sub&gt;[1,8-(O)&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;-2,7-[CH=N(2,6-&lt;sup&gt;i&lt;/sup&gt;Pr&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;)](PPh&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;} [&lt;b&gt;FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt;&lt;b&gt;(PR&lt;/b&gt;&lt;sub&gt;&lt;b&gt;3&lt;/b&gt;&lt;/sub&gt;&lt;b&gt;)&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt;] are presented, along with the synthesis and\ncharacterization of the mononuclear analogues {Ni(CH&lt;sub&gt;3&lt;/sub&gt;)[3-&lt;sup&gt;t&lt;/sup&gt;Bu-2-(O)C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;CH=N(2,6-&lt;sup&gt;i&lt;/sup&gt;Pr&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;)](PMe)&lt;sub&gt;3&lt;/sub&gt;} and {Ni(1-naphthyl)[3-&lt;sup&gt;t&lt;/sup&gt;Bu-2-(O)C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;CH=N(2,6-&lt;sup&gt;i&lt;/sup&gt;Pr&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;)](PPh)&lt;sub&gt;3&lt;/sub&gt;} [&lt;b&gt;FI-Ni\n(PR&lt;/b&gt;&lt;sub&gt;&lt;b&gt;3&lt;/b&gt;&lt;/sub&gt;&lt;b&gt;)&lt;/b&gt;]. Monometallic Ni\ncatalysts were also prepared by functionalizing one ligation center\nof the bimetallic ligand with a trimethylsilyl group (TMS), yielding\n{Ni(CH&lt;sub&gt;3&lt;/sub&gt;)[1,8-(O)(TMSO)C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;4&lt;/sub&gt;-2,7-[CH=N(2,6-&lt;sup&gt;i&lt;/sup&gt;Pr&lt;sub&gt;2&lt;/sub&gt;C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;3&lt;/sub&gt;)](PMe&lt;sub&gt;3&lt;/sub&gt;)} [&lt;b&gt;TMS-FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni(PMe&lt;/b&gt;&lt;sub&gt;&lt;b&gt;3&lt;/b&gt;&lt;/sub&gt;&lt;b&gt;)]&lt;/b&gt;. The &lt;b&gt;FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt; catalysts\nexhibit significant increases in ethylene homopolymerization activity\nversus the monometallic analogues, as well as increased branching\nand methyl branch selectivity, even in the absence of a Ni(cod)&lt;sub&gt;2&lt;/sub&gt; cocatalyst. Increasing ethylene concentrations significantly\nsuppress branching and alter branch morphology. &lt;b&gt;FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt;-mediated\ncopolymerizations with ethylene + polar-functionalized norbornenes\nexhibit a 4-fold increase in comonomer incorporation versus &lt;b&gt;FI-Ni&lt;/b&gt;, yielding copolymers with up to 10% norbornene copolymer\nincorporation. &lt;b&gt;FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt;-catalyzed copolymerizations with ethylene\n+ methylacrylate or methyl methacrylate incorporate up to 11% acrylate\ncomonomer, while the corresponding mononuclear &lt;b&gt;FI−Ni&lt;/b&gt; catalysts incorporate negligible amounts. Furthermore, the &lt;b&gt;FI&lt;/b&gt;&lt;sup&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sup&gt;&lt;b&gt;-Ni&lt;/b&gt;&lt;sub&gt;&lt;b&gt;2&lt;/b&gt;&lt;/sub&gt;-mediated polymerizations exhibit appreciable polar solvent\ntolerance, turning over in the presence of ethyl ether, acetone, and\neven water. The mechanism by which the present cooperative effects\ntake place is investigated, as is the nature of the copolymer microstructures\nproduced.