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Highly convenient amine-free Sonogashira coupling in air in a polar mixed aqueous medium by trans- and cis-[(NHC)(2)PdX2] (X = Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes

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Title Highly convenient amine-free Sonogashira coupling in air in a polar mixed aqueous medium by trans- and cis-[(NHC)(2)PdX2] (X = Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes
 
Creator RAY, L
BARMAN, S
SHAIKH, MM
GHOSH, P
 
Subject ring-opening polymerization
phenylene ethynylene oligomers
ab-initio pseudopotentials
copper-free
palladium complexes
aryl bromides
photophysical properties
terminal acetylenes
transition-elements
room-temperature
carbenes
cross-coupling
heterocycles
palladium
sonogashira reaction
 
Description Two new trans- and cisI(NHC)(2)PdX2] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes employed in a highly convenient amine-free Sonogashira cross-coupling reaction in air in a polar mixed aqueous medium are reported. Specifically, the rans-[{1-benzyl-3-(3,3-dimethyl-2-oxobutyl)imidazol-2-ylid-ene}(2)PdBr2] (3) and cis-[{1-benzyl-3-(Ntert-butylacetamido)imidazol-2-ylid-ene}(2)PdCl2] (4) complexes effectively catalyzed the Sonogashira cross-coupling reaction of aryl iodides with substituted acetylenes in air in a mixed solvent (DMF/H2O, 3:1 v/v) under amine-free conditions. Interestingly, these trans- and cis-[(NHC)(2)PdX2] (X=Cl, Br) complexes, with two N-heterocyclic carbene ligands, exhibited superior activity compared with the now popular PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation)-themed analogues, trans-[(NHC)Pd(pyridine)X-2] (X=Cl, Br, 3a and 4a, with one N-heterocyclic carbene ligand and a "throw away" pyridine ligand in a trans disposition to each other. The higher activities of 3 and 4 compared with PEPPSI analogues 3a and 4a are attributed to more-clectron-rich metal centers, as revealed by DFT studies, in the former complexes and is in concurrence with a more electron-rich metal center being effective in facilitating the oxidative addition of aryl halide, often a rate-determining step in palladium-mediated cross-coupling reactions. Complexes 3 and 4 were prepared from the corresponding silver analogues by transmetalation with [(cod)PdCl2], whereas the corresponding PEPPSI analogues 3a and 4a were obtained directly from the imidazolium halide salts by reaction with PdCl2 in pyridine in the presence of K2CO3 as base.
 
Publisher WILEY-V C H VERLAG GMBH
 
Date 2011-09-01T17:42:27Z
2011-12-26T12:59:44Z
2011-12-27T05:52:31Z
2011-09-01T17:42:27Z
2011-12-26T12:59:44Z
2011-12-27T05:52:31Z
2008
 
Type Article
 
Identifier CHEMISTRY-A EUROPEAN JOURNAL, 14(22), 6646-6655
0947-6539
http://dx.doi.org/10.1002/chem.200800301
http://dspace.library.iitb.ac.in/xmlui/handle/10054/12832
http://hdl.handle.net/10054/12832
 
Language en