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Control of Chain Walking by Weak Neighboring Group Interactions in Unsymmetrical Catalysts

Control of Chain Walking by Weak Neighboring Group Interactions in Unsymmetrical Catalysts

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FALIVENE, Laura, Thomas WIEDEMANN, Inigo GÖTTKER-SCHNETMANN, Lucia CAPORASO, Luigi CAVALLO, Stefan MECKING, 2018. Control of Chain Walking by Weak Neighboring Group Interactions in Unsymmetrical Catalysts. In: Journal of the American Chemical Society : JACS. 140(4), pp. 1305-1312. ISSN 0002-7863. eISSN 1520-5126. Available under: doi: 10.1021/jacs.7b08975

@article{Falivene2018Contr-41212, title={Control of Chain Walking by Weak Neighboring Group Interactions in Unsymmetrical Catalysts}, year={2018}, doi={10.1021/jacs.7b08975}, number={4}, volume={140}, issn={0002-7863}, journal={Journal of the American Chemical Society : JACS}, pages={1305--1312}, author={Falivene, Laura and Wiedemann, Thomas and Göttker-Schnetmann, Inigo and Caporaso, Lucia and Cavallo, Luigi and Mecking, Stefan} }

2018-02-02T10:51:11Z Caporaso, Lucia Falivene, Laura Göttker-Schnetmann, Inigo 2018-02-02T10:51:11Z Mecking, Stefan 2018 Mecking, Stefan eng Wiedemann, Thomas Falivene, Laura Göttker-Schnetmann, Inigo Caporaso, Lucia Cavallo, Luigi Control of Chain Walking by Weak Neighboring Group Interactions in Unsymmetrical Catalysts Wiedemann, Thomas Cavallo, Luigi A combined theoretical and experimental study shows how weak attractive interactions of a neighbouring group can strongly promote chain walking and chain transfer. This accounts for the previously observed very different microstructures obtained in ethylene polymerization by [κ<sup>2</sup>-N,O-{(2,6-(3',5'-R<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>-N=C(H)-(3,5-X,Y<sub>2</sub>-2-O-C<sub>6</sub>H<sub>2</sub>)}]NiCH<sub>3</sub>(pyridine)], namely hyperbranched oligomers for remote substituents R = CH<sub>3</sub> versus. high molecular weight polyethylene for R = CF<sub>3</sub>. From a full mechanistic consideration the alkyl olefin complex with the growing chain cis to the salicylaldiminato oxygen donor is identified as the key species. Alternative to ethylene chain growth by insertion in this species, decoordination of the monomer to form a cis ß-agostic complex provides an entry into branching and chain transfer pathways. This release of monomer is promoted and made competitive by a weak η2-coordination of the distal aryl rings to the metal center, operative only for the case of sufficiently electron rich aryls. This concept for controlling chain walking is underlined by catalysts with other weakly coordinating furane and thiophene motifs, which afford highly branched oligomers with > 120 branches per 1000 carbon atoms.

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