Recent advances in soluble ruthenium(0) nanocatalysts and their reactivity

[Display omitted] •Simple and convenient methods of generating soluble ruthenium nano-catalysts.•High activity and unique selectivity in a variety of transformations.•Applications in (de)hydrogenation, transfer hydrogenation, and oxidation.•Challenges in nanocatalysis: identification, separation, and asymmetric induction. Metal nanoparticles exhibit unusual properties different from metal complexes and heterogeneous metals and hence draw considerable attention for applications in catalysis, magnetism, medicine, optoelectronics, and sensors. Herein we present an overview of the recent progress in catalysis using soluble ruthenium nanocatalysts (colloids). These nanocatalysts have been widely used for catalyzing the hydrogenation of various substrates particularly arenes due to the milder conditions and the unique selectivities achieved compared to those exhibited by classical heterogeneous catalysts. Ru(0) colloids have been also examined for catalyzing many different reactions including transfer hydrogenation, dehydrogenation, coupling reactions and CH activation, etc. Although in many of these transformations Ru(0) nanocatalysts exhibit high activities, there remain several challenges such as recovery of the soluble catalyst, catalysis by leached molecular clusters, and asymmetric catalysis with high enantioselectivity.