Thermo-responsive self-assembled metallomicelles accelerate asymmetric sulfoxidation in water

• Thermoresponsive surfactant-type chiral salen TiIV catalysts were developed.
• The catalysts self-assembled in water to form metallomicelles with different morphologies.
• Asymmetric sulfoxidation was efficiently conducted in water with the metallomicelles.
• Outstanding activity and selectivity were achieved as a result of the “micellar catalysis”.
• The catalyst can be easily recovered for efficient reuse via thermocontrolled separation.

A series of novel chiral salen TiIV catalysts with thermo-responsive surfactant properties were prepared by covalently appending a chiral salen TiIV complex on the hydrophobic block of thermo-responsive amphiphilic copolymers of poly(N-isopropylacrylamide-co-N,N-dimethyl acrylamide) (poly (NIPAAM-co-DMAAM)). Characterization results suggested self-assembly behavior of the catalysts in water at room temperature. The self-assembled metallomicelles induced a micellar catalytic approach in asymmetric sulfoxidation in water using H2O2 as an oxidant, leading to significant rate acceleration and remarkable high selectivity. Quantitative conversion (>99%) of methyl phenyl sulfide with up to 96% chemoselectivity and 95% enantioselectivity was achieved over 0.5 mol% of PN70D7-C even within 30 min, whereas neat complex was far less efficient (9% conversion with 72% chemoselectivity and 79% enantioselectivity). Moreover, the catalysts could be easily recovered by thermo-controlled separation and be efficiently reused for several cycles.

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