This article recaps a variety of interesting catalytic studies based on solubilized and freely movable noble metal nanoparticle catalysts employed for organic reactions in either pure water or water-organic biphasic systems. Small organic ligand-capped metal nanoparticles are fundamentally attractive materials due to their enormous potential as a well-defined system that can provide spatial control near active catalytic sites. The nanoparticle catalysts are first grouped based on the synthetic method (direct reduction, phase transfer, and redispersion) and then again based on the type of reaction such as alkene hydrogenation, arene hydrogenation, nitroaromatic reduction, carbon-carbon coupling reactions, etc. The impacts of various ligands on the catalytic activity and selectivity of semi-heterogeneous nanoparticles in water are discussed in detail. The catalytic systems using polymers, dendrimers, and ionic liquids as supporting or protecting materials are excluded from the subject of this review.
Keywords: biphasic catalysis; catalysis; coupling reaction; green catalysis; hydrogenation; nanoparticle; noble metal; semi-heterogeneous.