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Bis(imido) tungsten complexes: efficient pre-catalysts for the homogeneous dimerization of ethylene

Messinis, Antonis; Batsanov, Andrei S.; Wright, William R.H.; Howard, Judith A.K.; Hanton, Martin J.; Dyer, Philip W.

Bis(imido) tungsten complexes: efficient pre-catalysts for the homogeneous dimerization of ethylene Thumbnail


Authors

Antonis Messinis

William R.H. Wright

Judith A.K. Howard

Martin J. Hanton



Abstract

The ethylene dimerization performance of a range of bis(imido)tungsten pre-catalysts, after activation with aluminum co-catalysts, has been assessed. The best performing system achieved an activity of 409,410 (mol C2H4)(mol W)–1h–1 [79.6 wt% 1-butene] with a 1-butene selectivity of 82.4 wt% [290,770 (mol C2H4)(mol W)–1h–1 activity]. In addition to selected previously reported variants, the symmetrical bis(imido)tungsten(VI) complexes [WCl2(NPh)2(tmeda)] (3) and [WCl2(NR)2(dme)] [R = 2,4,6-trifluorophenyl, 7; 2,4,6-triphenylphenyl, 8; 2,4,6-tris(trifluoromethyl)phenyl, 9], were prepared. A series of unsymmetrical bis(imido)tungsten(VI) complexes [WCl2(NDipp)(NR)(dme)] (R = iPr, 11; tBu, 12; 2,4,6-trimethylphenyl, 13; 2,4,6-trichlorophenyl, 14; 2,4,6-trifluorophenyl, 15; 2,6-dinitrophenyl, 16; 2,4,6-triphenylphenyl, 17) were also synthesized using an improved version of a previous preparative route that eases purification. The molecular structures of complexes 5-13 and 15-17 were determined by X-ray crystallographic analysis. Catalysis employing complexes 1-17 unveils a complicated relationship between steric and electronic factors that affects activity and catalyst lifetime, however selectivity is dominated by electronic considerations. Higher reaction temperatures were shown to favor 1-butene selectivity and higher activity, whilst replacement of EtAlCl2 with MeAlCl2 as co-initiator was found to be detrimental. Tungsten(IV) species were demonstrated to be unlikely as the active species during catalysis. Studies of catalysis runs undertaken to varying productivities found that during the nascent phase of reaction a notably lower activity is observed, whilst the selectivity favors C8+ formation during this period, most likely due to activation processes still occurring. The rate of formation of 1-butene was shown to increase with productivity, as a result of the greater solubility of ethylene in the 1-butene generated compared to the chlorobenzene solvent. The formation of C6 by-products was shown to be independent of 1-butene concentrations, consistent with a mechanism whereby 1-butene is only incorporated into secondary products when it reacts prior to dissociation from the tungsten center.

Citation

Messinis, A., Batsanov, A. S., Wright, W. R., Howard, J. A., Hanton, M. J., & Dyer, P. W. (2018). Bis(imido) tungsten complexes: efficient pre-catalysts for the homogeneous dimerization of ethylene. ACS Catalysis, 8(12), 11249-11263. https://doi.org/10.1021/acscatal.8b02202

Journal Article Type Article
Acceptance Date Oct 9, 2018
Online Publication Date Oct 9, 2018
Publication Date Oct 9, 2018
Deposit Date Oct 17, 2018
Publicly Available Date Mar 29, 2024
Journal ACS Catalysis
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 8
Issue 12
Pages 11249-11263
DOI https://doi.org/10.1021/acscatal.8b02202

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Copyright Statement
This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS catalysis copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acscatal.8b02202





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