Phosphane-free hiyama cross-coupling of aryl and heteroaryl halides catalyzed by palladium nanoparticles in ionic liquids

Article abstract of DOI:10.1002/ejoc.201300307

Palladium nanoparticles (NPs) 2-5 nm in size and preformed by thermal reduction in nitrile-functionalized 3-(3-cyanopropyl)-1-methyl-1H-imidazol-3-ium hexafluorophosphate {[CN-bmim]PF₆} act as an in situ catalyst for carbon-carbon bond-forming reactions of aromatic and heterocyclic halides with aryl- and vinyltrimethoxysilanes. A variety of biphenyl derivatives, substituted styrenes, and aromatic heterocycles were obtained in 76 to 98 % yield. We demonstrate for the first time the use of 1-butyl-3-methylimidazolium fluoride as an activator of the organosilanes with easy handling, storage, and workup in comparison to conventional fluorine sources such as tetrabutylammonium fluoride, which is indispensable for Hiyama coupling. Pd NPs immobilized in [CN-bmim]PF₆ gave high yields of the cross-coupled products at a low catalyst loading of only 4 mol-%, and the catalyst could be reused and recycled up to four times with only a slight loss in catalytic activity. Phosphane-free Hiyama coupling of aryl- and vinyltrimethoxysilanes with aromatic and heterocyclic halides catalyzed by palladium nanoparticles in nitrile-functionalized ionic liquids to yield a range of biphenyl derivatives, substituted styrenes, and aromatic heterocycles is reported. The catalytic system can be recycled at least four times with only a slight loss in catalytic activity. Copyright