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Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis
Date Issued
2014-11-15
Date Available
2015-06-16T14:15:22Z
Abstract
Benzimidazolium salts containing both a neutral imine and a masked carboxylate functional group for potential metal chelation were prepared. Palladation of the ester-protected ligand afforded a N,C-bidentate carbene complex 4. Subsequent ester hydrolysis preserved the bidentate coordination mode and yielded complex 5 with a pending COOH group exclusively. However, when ester deprotection was carried out prior to metalation, the N,C,O-tridentate pincer-type coordinated palladium complex 7 was obtained. Proton-abstraction of the dangling COOH group in the bidentate ligand of complex 5 by treatment with a base led to the formation of the N,C,O-tridentate coordinated Pd system 7, and inversely, exposure of the tridentate bound Pd complex 7 with acid afforded the N,C-bidentate ligand coordination mode in complex 5, demonstrating hemilability of the oxygen donor site in the pincer ligand. All three palladium(II) complexes 4, 5, and 7 were evaluated in cross-coupling catalysis and revealed distinct activity differences that are dependent on the type of coupling (Suzuki vs. Heck) and the substrate (Ar-Br vs. Ar-Cl). These differences suggest that judicious choice of donor groups in pincer-type complexes is a viable strategy for catalyst optimization.
Sponsorship
European Research Council
Science Foundation Ireland
Type of Material
Journal Article
Publisher
Elsevier
Journal
Journal of Organometallic Chemistry
Volume
771
Start Page
33
End Page
39
Copyright (Published Version)
2014 Elsevier
Language
English
Status of Item
Peer reviewed
This item is made available under a Creative Commons License
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