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
DSpace at IIT Bombay
View Archive InfoField | Value | |
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
|
|