Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis

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Title: Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis
Authors: Leigh, Vivienne
Ghattas, Wadih
Müller-Bunz, Helge
Albrecht, Martin
Permanent link: http://hdl.handle.net/10197/6607
Date: 15-Nov-2014
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.
Funding Details: European Research Council
Science Foundation Ireland
Type of material: Journal Article
Publisher: Elsevier
Copyright (published version): 2014 Elsevier
Keywords: Pincer ligands;N-heterocyclic carbenes;Palladium;Hemilabile coordination;Cross-coupling catalysis
DOI: 10.1016/j.jorganchem.2014.05.022
Language: en
Status of Item: Peer reviewed
Appears in Collections:Chemistry Research Collection

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