Control of Chain Walking by Weak Neighbouring Group Interac-tions in Unsymmetric Catalysts

Laura Falivene, Thomas Wiedemann, Inigo Göttker-Schnetmann, Lucia Caporaso, Luigi Cavallo, Stefan Mecking

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

Abstract

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 micro-structures obtained in ethylene polymerization by [κ$^{2-N,O-{(2,6-(3',5'-R2C6H3)2C6H3-N=C(H)-(3,5-X,Y2-2-O-C6H2)}]NiCH3(pyridine)], namely hyperbranched oligomers for remote substituents R = CH3 versus. high molecular weight polyethylene for R = CF3. 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 thio-phene motifs, which afford highly branched oligomers with > 120 branches per 1000 carbon atoms.
Original languageEnglish (US)
Pages (from-to)1305-1312
Number of pages8
JournalJournal of the American Chemical Society
Volume140
Issue number4
DOIs
StatePublished - Jan 23 2018

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