Covalent organic frameworks (COFs) are promising photocatalysts for solar energy utilization due to their tunable band gap for light harvesting. Nevertheless, their photocatalytic performance is often impeded by insufficient charge...

Water-soluble single-chain polymeric nanoparticles (SCPNs), which isolated catalytic sites within a hydrophobic interior, made water-incompatible organometallic catalysis highly efficient in water. However, it is still a great challenge to conveniently control their hydrophilicity, so as to combine reactivity and recovery of the catalytic SCPNs in aqueous systems. Herein, we have developed a series of catalytic SCPNs, which possessed CO 2 -switchable hydrophilic/hydrophobic behavior, to realize the gas-controlled reaction and separation for asymmetric sulfa-Michael addition (SMA) in water. A novel series of CO 2 -switchable random copolymers were thus synthesized by copolymerization of CO 2 -responsive amidine derivatives with hydrophobic chiral salen Fe III monomers via reversible addition-fragmentation chain transfer polymerization. Characterization suggested their CO 2 -controlled self-collapse behavior in water due to CO 2 -switched change in hydrophilicity/hydrophobicity of the amidine moiety. The resultant CO 2 -switchable SCPNs provided hydrophobic, catalytic compartments for asymmetric SMA in water upon CO 2 addition, giving various chiral β-keto sulfides with almost quantitative yields (90−98%) and high enantioselectivities (93−99%). When CO 2 is removed by N 2 bubbling, they were collapsed and spontaneously precipitated from the aqueous system for steady reuse. The gas-controlled reactionseparation approach provides an energy-efficient way to combine reactivity and recovery of catalytic SCPNs in aqueous systems, which should be quite practical in large-scale industrial applications.

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