Palladium-catalysed cross-coupling reactions, central tools in fine-chemical synthesis, predominantly employ soluble metal complexes despite recognized challenges with product purification and catalyst reusability^1,2,3. Attempts to tether these homogeneous catalysts on insoluble carriers have been thwarted by suboptimal stability, which leads to a progressively worsening performance due to metal leaching or clustering⁴. The alternative application of supported Pd nanoparticles has faced limitations because of insufficient activity under the mild conditions required to avoid thermal degradation of the substrates or products. Single-atom heterogeneous catalysts lie at the frontier^{5,6,7,8,9,10,11,12,13,14,15,16,17,18}. Here, we show that the Pd atoms anchored on exfoliated graphitic carbon nitride (Pd-ECN) capture the advantages of both worlds, as they comprise a solid catalyst that matches the high chemoselectivity and broad functional group tolerance of state-of-the-art homogeneous catalysts for Suzuki couplings, and also demonstrate a robust stability in flow. The adaptive coordination environment within the macroheterocycles of ECN facilitates each catalytic step. The findings illustrate the exciting opportunities presented by nanostructuring single atoms in solid hosts for catalytic processes that remain difficult to heterogenize.

Selective hydrogenations lay at the heart of many industrial processes. The archetypal catalysts for this class of reactions are generally prepared by ‘metal poisoning’ strategies: the active metal is protected and selectively deactivated with various compounds. This approach has been applied for decades, with limited understanding. Low product selectivity and presence of toxic elements in the catalyst pose severe constraints in the utilization of these materials in the future. Thus, to develop more sustainable catalysts, this field has recently gained momentum. This Review analyzes the concepts and frontiers that have been developed in the last decade: from nanostructuring less conventional metals in order to improve their ability to activate H₂, to the use of oxides as active phases, from alloying, to the ensemble control in hybrid materials, and site isolation approaches in single‐site heterogeneous catalysts. Particular attention is given to the hydrogenation of alkynes and nitroarenes, two reactions at the core of the chemical industry, importantly applied in the manufacture of polymers, pharmaceuticals, nutraceuticals, and agrochemicals. The strategies here identified can be transposed to other relevant hydrogenations and can guide in the design of more advanced materials.

Single‐atom catalysts hold the potential to significantly impact the chemical sector, pushing the boundaries of catalysis in new, uncharted directions. These materials, featuring isolated metal species ligated on solid supports, can exist in many coordination environments, all of which have shown important functions in specific transformations. Their emergence has also provided exciting opportunities for mimicking metalloenzymes and bridging the gap between homogeneous and heterogeneous catalysis. This Review outlines the impressive progress made in recent years regarding the use of single‐atom catalysts in organic synthesis. We also illustrate potential knowledge gaps in the search for more sustainable, earth‐abundant single‐atom catalysts for synthetic applications.