Heterogenization of molecular catalysts via their immobilization within extended structures often results in a lowering of their catalytic properties due to a change in their coordination sphere. Metal-organic polyhedra (MOPs) are an emerging class of well-defined hybrid compounds with a high number of accessible metal sites organised around an inner cavity, making them appealing candidates for catalytic applications. Here we demonstrate a design strategy that enhances the catalytic properties of dirhodium paddlewheels heterogenized within a MOP (Rh-MOP) and its three-dimensional assembled supramolecular structures, which proved to be very efficient catalysts for the selective photochemical reduction of carbon dioxide to formic acid. Surprisingly, the catalytic activity per Rh atom is higher in the supramolecular structures than in its molecular sub-unit Rh-MOP or in Rh-MOF, and yields turnover frequencies of up to 60 h -1 and production rates of approx. 76 mmole formic acid per gram of catalyst per hour, unprecedented in heterogeneous photocatalysis, demonstrating the high potential of MOPs as catalysts for the photoreduction of CO 2 . This opens new perspectives for the electronic design of discrete molecular architectures with accessible metal sites for the production of solar fuels. The enhanced catalytic activity is investigated by XPS spectroscopy and electrochemical characterization, showing that self-assembly into supramolecular polymers increases the electron density on the active site, making the overall reaction thermodynamically more favourable. The catalyst can be recycled without loss of activity and with no change of its molecular structure as shown by pair distribution function analysis.

Direct C-H functionalization catalyzed by a robust and recyclable heterogeneous catalyst is highly desirable for sustainable fine chemical synthesis. Bipyridine units covalently incorporated into the backbone of a porous organic polymer were used as a porous macroligand for the heterogenization of a molecular nickel catalyst. A controlled nickel loading within the porous macroligand is achieved and the nickel coordination to the bpy sites is assessed at the molecular level using IR and solid-state NMR spectroscopy. The heterogenized Ni-bpy catalyst was successfully applied to the direct and fully selective C2 arylation of benzothiophenes, thiophene and selenophene, as well as for the arylation of free NH-indole. Recyclability of the catalyst was achieved by employing hydride activators to reach a cumulative turnover number of more than 300 after seven cycles of catalysis, which corresponds to a total productivity of 12 grams of 2-phenylbenzothiophene, chosen as model target biaryl, per gram of catalyst.