Please use this identifier to cite or link to this item: https://doi.org/10.1016/j.jorganchem.2008.10.044
Title: Rotamers of palladium complexes bearing IR active N-heterocyclic carbene ligands: Synthesis, structural characterization and catalytic activities
Authors: Huynh, H.V. 
Wu, J.
Keywords: C-C coupling
Homogeneous catalysis
N-heterocyclic carbene
Palladium
Rotamers
Issue Date: 1-Feb-2009
Citation: Huynh, H.V., Wu, J. (2009-02-01). Rotamers of palladium complexes bearing IR active N-heterocyclic carbene ligands: Synthesis, structural characterization and catalytic activities. Journal of Organometallic Chemistry 694 (3) : 323-331. ScholarBank@NUS Repository. https://doi.org/10.1016/j.jorganchem.2008.10.044
Abstract: The preparation and properties of mono- versus bis(carbene) Pd(II) complexes bearing unsymmetrical cyano- and ester-functionalized NHC ligands as potential IR probes were studied in detail. Direct reaction of Pd(OAc)2 with functionalized imidazolium salts afforded either bis(carbene) (3a, c) or monocarbene complexes (5, 6) with a N-coordinated imidazole co-ligand. The latter were exclusively obtained with N-ethylene substituted salts, which were found to undergo N-C cleavage reaction. The milder Ag-carbene transfer reaction on the other hand was tolerable to the length of the substituents and the nature of the functional groups. All bis(carbene) complexes (3a-c, 4a-c) were obtained as a inseparable mixture of square-planar trans-anti and trans-syn rotamers. The identity, ratio and dynamic equilibrium of these rotamers have been investigated and the relatively high rotational barrier for rotamers of 3a was estimated to be about 74 kJ mol-1 at 380 K. All eight complexes were fully characterized by NMR and IR spectroscopies, ESI mass spectrometry and X-ray single crystal and powder diffraction. A preliminary catalytic study showed that ester-functionalized complexes 4a and 4b gave rise to highly active catalyst in the double Mizoroki-Heck coupling of aryl dibromides, while the in situ ester-hydrolyzed complexes were also active in the coupling of activated aryl chlorides. © 2008 Elsevier B.V. All rights reserved.
Source Title: Journal of Organometallic Chemistry
URI: http://scholarbank.nus.edu.sg/handle/10635/94735
ISSN: 0022328X
DOI: 10.1016/j.jorganchem.2008.10.044
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