TY - JOUR
T1 - Control of Chain Walking by Weak Neighbouring Group Interac-tions in Unsymmetric Catalysts
AU - Falivene, Laura
AU - Wiedemann, Thomas
AU - Göttker-Schnetmann, Inigo
AU - Caporaso, Lucia
AU - Cavallo, Luigi
AU - Mecking, Stefan
N1 - KAUST Repository Item: Exported on 2021-09-14
Acknowledgements: Financial support by the DFG (Me1388/14-1) and by Byk is gratefully acknowledged. Stefano Santacroce, Florian Wimmer and Giusi Boffa contributed as a part of their undergraduate studies. We thank Rainer Winter for discussions of cyclic voltammetry data.
PY - 2018/1/23
Y1 - 2018/1/23
N2 - 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$^{2-N,O-{(2,6-(3',5'-R2C6H3)2C6H3-N=C(H)-(3,5-X,Y2-2-O-C6H2)}]NiCH3(pyridine)], namely hyperbranched oligomers for remote substituents R = CH3 versus. high molecular weight polyethylene for R = CF3. From a full mechanistic consideration the alkyl olefin complex with the growing chain cis to the salicylaldiminato oxygen donor is identified as the key species. Alternative to ethylene chain growth by insertion in this species, decoordination of the monomer to form a cis ß-agostic complex provides an entry into branching and chain transfer pathways. This release of monomer is promoted and made competitive by a weak η2-coordination of the distal aryl rings to the metal center, operative only for the case of sufficiently electron rich aryls. This concept for controlling chain walking is underlined by catalysts with other weakly coordinating furane and thio-phene motifs, which afford highly branched oligomers with > 120 branches per 1000 carbon atoms.
AB - A combined theoretical and experimental study shows how weak attractive interactions of a neighbouring group can strongly promote chain walking and chain transfer. This accounts for the previously observed very different micro-structures obtained in ethylene polymerization by [κ$^{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.
UR - http://hdl.handle.net/10754/626434
UR - http://pubs.acs.org/doi/10.1021/jacs.7b08975
UR - http://www.scopus.com/inward/record.url?scp=85041304822&partnerID=8YFLogxK
U2 - 10.1021/jacs.7b08975
DO - 10.1021/jacs.7b08975
M3 - Article
C2 - 29261306
AN - SCOPUS:85041304822
SN - 0002-7863
VL - 140
SP - 1305
EP - 1312
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 4
ER -