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Neutral Nickel Oligo- and Polymerization Catalysts: The Importance of Alkyl Phosphine Intermediates in Chain Termination.
MedLine Citation:
PMID:  22095527     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
An unconventional chain termination reaction has been explored for the SHOP (Shell higher olefin process)-type, anilinotropone, and salicylaldiminato nickel-based oligo- and polymerization catalysts by using density functional theory (DFT). Starting from the tetracoordinate alkyl phosphine complex, the termination reaction was found to involve a rearrangement of the alkyl chain to form a pentacoordinate β-agostic complex, β-hydride elimination, and olefinic chain dissociation and to compete with propagation at sufficiently high phosphine concentration and/or basicity. It provides the first complete and convincing mechanistic rationale for the decreasing chain lengths observed upon increasing phosphine concentration and basicity. The unconventional reaction was found to be a major termination pathway for the SHOP-type catalyst and is very unlikely to lead to branching and olefin isomerization, which is critical for explaining why the SHOP catalyst, in contrast to the anilinotropone and salicylaldiminato catalysts, tends to lead to the oligomerization of ethylene to form linear α-olefins. Based on our results we have proposed a new and extended catalytic cycle for the SHOP-type ethylene oligomerization catalyst. Finally, the importance of the new termination reaction for the SHOP-type catalyst suggests that this reaction may also operate with other ethylene oligomerization nickel catalysts. This prediction was confirmed for a pyrazolonatophosphine catalyst, for which the new termination route was found to be even more facile, which explains the short oligomers produced by this catalyst.
Authors:
Wouter Heyndrickx; Giovanni Occhipinti; Yury Minenkov; Vidar R Jensen
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-11-16
Journal Detail:
Title:  Chemistry (Weinheim an der Bergstrasse, Germany)     Volume:  -     ISSN:  1521-3765     ISO Abbreviation:  -     Publication Date:  2011 Nov 
Date Detail:
Created Date:  2011-11-18     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9513783     Medline TA:  Chemistry     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Affiliation:
Department of Chemistry, University of Bergen, Allégaten 41, N-5007 Bergen (Norway), Fax: (+47) 55589490.
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