As a new kind of potential catalysts containing both maximum atom efficiency and high synergetic effect, heteronuclear metal single clusters (SCs) with metal–metal bonds have been successfully anchored into porphyrinic metal-organic frameworks, giving rise to a series of MOF composites named after Ir_xCu_1−x-SCs@Co-PCN-222-PyzA. Among them, Ir_0.15Cu_0.85-SCs@Co-PCN-222-PyzA displayed the highest efficiency and accelerated the selective reduction of CO₂ to methanol via hydrosilylation under 15% CO₂ pressure with the turnover frequency of 356 h⁻¹ and turnover number of 2453 based on the Ir content. Ir_0.15Cu_0.85-SCs@Co-PCN-222-PyzA could be recycled and reused for 10 successive runs with no loss of the reactivity and selectivity. Mechanistic studies revealed that the superior reactivity might be attributed to “co-adsorption–co-activation” of reaction substrates by the bimetallic single clusters of Ir_xCu_1−x-SCs within the confined nanospaces of Co-PCN-222.

Alkene hydrosilylation is one of the most concise and atom-economical methods to synthesize organosilicon molecules. Herein, we reported the precise immobilization of metal single atoms (M-SAs; M = Ru, Rh, Ir, Pd, Pt, and Au) into a porphyrinic metal-organic framework (MOF) of PCN-222 (PCN = porous coordination network), and then applied the resultant MOF composites of M-SAs@PCN-222 to alkene hydrosilylation. Under solvent-free conditions, Pt-SAs@PCN-222 displayed an especially high catalytic efficiency with the turnover frequency up to 119 s⁻¹ and the maximum turnover number of 906,250 at room temperature. Experimental and theoretical studies revealed that there existed strong interactions between Pt-SAs@PCN-222 and the substrates, which helped to condense the substrates in the cavities of the porous catalysts. Further density functional theory calculations and molecular dynamics simulations disclosed that PCN-222 could transfer electrons to Pt-SAs to enhance the silane oxidative addition and drive the reaction to proceed smoothly via Chalk–Harrod pathway.