Metal nanoparticles are useful catalysts in many reactions, but keeping them stable in solution over many catalytic cycles has proven challenging. Chemists have taken a number of approaches to the problem, such as using dendrimer supports and metal-organic frameworks to protect the nanoparticles. Using a different tack, researchers in Japan have shown that building a soluble organic cage around rhodium nanoparticles can make the heterogeneous catalysts slip easily into solution, effectively converting them into a homogeneous catalyst (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b04029). Qiang Xu and his colleagues at Japan’s National Institute of Advanced Industrial Science & Technology created the caged nanoparticles by reducing rhodium acetate in the presence of a porous cyclo - imine cage molecule. The resulting catalyst consists of rhodium nanoparticles about 1 nm across trapped within a cage that has reactant-permeable windows. The caged catalyst is stable and has proved to be superior to all other catalysts in the methanolysis of ammonia borane—a reaction that breaks down that hydrogen storage material. And the catalyst can be recovered simply by drying and washing it.