Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra‐High‐Molecular Weight Polyethylene in the Absence of Activators |
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Authors: | Alexey Fedorov Micah S Ziegler Christophe Copéret T Don Tilley |
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Institution: | 1. Department of Chemistry and Applied Biosciences, ETH Zürich, Zürich;2. Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA |
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Abstract: | Low‐coordinate organoCr(III) complexes supported by the silylamido ligand –N(SiMe3)DIPP (DIPP = 2,6‐diisopropylphenyl) are ethylene polymerization catalyst precursors without the need of additional cocatalyst. The reaction of CrCl3(THF)3 with 3 or 2 equiv. of LiN(SiMe3)DIPP yields either a four‐membered cyclometalated Cr complex or CrN(SiMe3)DIPP]2Cl, respectively, with no trace of CrN(SiMe3)DIPP]3. Addition of 1 equiv. of LiN(SiMe3)DIPP to CrN(SiMe3)DIPP]2Cl also leads to the four‐membered metallacycle, which upon heating transforms to a new six‐membered Cr metallacycle, likely via a σ‐bond metathesis step. CrN(SiMe3)DIPP]2Cl can be readily converted to bis(amido)Cr(III) vinyl and alkyl complexes CrN(SiMe3)DIPP]2R (R = vinyl, Bn, and Me). All of these structurally characterized low‐coordinate Cr(III) complexes with a Cr–C bond initiate the polymerization of ethylene in the absence of activators or cocatalysts, producing ultra‐high‐molecular weight polyethylene. |
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Keywords: | Ethylene polymerization Phillips catalyst Cr(III) Amides Low‐coordinate complexes Cyclometalation |
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