Metal–ligand cooperative properties of a bis-N-heterocyclic carbene ruthenium CNC pincer catalyst and its activity in CO2 hydrogenation to formates were studied by DFT calculations complemented by NMR spectroscopy and kinetic measurements. The dearomatized Ru–CNC* pincer (1*) is significantly more reactive toward metal–ligand cooperative activation of H2 and CO2 than the structurally related phosphine-based Ru–PNP complex. The enhanced reactivity of Ru–CNC* stems from the combination of electronic properties of this system and the reduced geometric constraints imposed onto the Ru center by the large and flexible CNC chelate. Heterolytic dissociation of H2 by 1* results in the bis-hydrido complex 2 that is active in hydrogenation of CO2. However, under commonly applied reaction conditions, the catalyst rapidly deactivates via metal–ligand cooperative paths. The transient formation of the dearomatized complex Ru–CNC* (1*) in the course of the reaction leads to the irreversible cooperative activation of CO2, resulting in the stable adduct 3 that is not catalytically competent. By an increase in the H2/CO2 ratio, this deactivation path can be effectively suppressed, resulting in a stable and rather high catalytic performance of Ru–CNC.

Reaction mechanisms for the catalytic hydrogenation of CO2 by faujasite‐supported Ir4 clusters were studied by periodic DFT calculations. The reaction can proceed through two alternative paths. The thermodynamically favoured path results in the reduction of CO2 to CO, whereas the other, kinetically preferred channel involves CO2 hydrogenation to formic acid under water‐free conditions. Both paths are promoted by catalytic amounts of water confined inside the zeolite micropores with a stronger promotion effect for the reduction path. Co‐adsorbed water facilitates the cooperation between the zeolite Brønsted acid sites and Ir4 cluster by opening low‐energy reaction channels for CO2 conversion.

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