Now, a collective effort from researchers in Singapore, Switzerland and China introduces heterogeneous geminal-atom catalysts (GACs), a class of atomically dispersed catalysts for cross-coupling reactions that contain atomic pairs of the active metal in spatial proximity and with adaptable coordination. The GAC presented consists of low-valence Cu centres on a nanocrystalline polymeric carbon nitride host (Cug/PCN) and is prepared via a stepwise ion exchange and ligand removal strategy, where the Cu atoms replace H atoms from pendant amino groups and form pairs with a Cu···Cu distance of around 4 Å, achieving a high Cu loading of 18.3 wt%. The catalyst is examined for the cross coupling of a broad scope of aryl halides with nitrogen-based nucleophiles, alcohols, alkynes and thiols for C–N, C–O, C–C and C–S bond formations, respectively, as well as for the late-stage modification of biorelevant molecules, consistently achieving high yields.
A series of control experiments, spectroscopic measurements and density functional theory calculations unveil a cooperative mechanism between the geminal centres, in which both atoms exhibit flexible coordination, allowing them to form a Cu–Cu bond at around 2.5 Å during reaction, which enables the close adsorption and coupling of the reactants. This restructuring is dynamic, and the Cu centres recover their original configuration after reaction. The stability and recyclability of the GAC is demonstrated, and the study is complemented with an extension of the reaction scope as well as scale-up and continuous-flow synthesis experiments. The article concludes with a life-cycle assessment that shows the environmental benefits of the GAC over conventional homogeneous catalysis routes.
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