Azobenzene-bridged chiral salen TiIV catalysts enabled the cooperative bimetallic catalysis of asymmetric sulfoxidation in a light-controllable way through the E/Z photoisomerism of an azobenzene linker.
Metallomicellar
catalysis has gained increasing attention in recent
years since it made water-incompatible organometallic catalysis highly
efficient in water. However, a convenient approach to combine activity
and recovery of metallomicelles from aqueous systems has remained
challenging to date. Herein, we developed a series of nitrospiropyran-containing
metallomicelles which possessed visible-light-responsivity, to realize
the visible-light-controlled reaction and separation for asymmetric
sulfoxidation in water. A series of nitrospiropyran-containing diblock
chiral salen TiIV copolymers were thus prepared by copolymerizing
photosensitive nitrospiropyran derivative with hydrophobic chiral
salen TiIV monomer via free-radical polymerization. Characterization
results suggested their visible-light-controlled self-assembly behavior
in water due to the negative photochromism of nitrospiropyran block.
The resultant light-responsive metallomicelles induced a micellar
catalysis approach in the dark for asymmetric sulfoxidation in water
using H2O2 as an oxidant, leading to significant
rate acceleration and remarkable high selectivity over a wide range
of aryl alkyl sulfides. When exposed to visible light, they were collapsed
and precipitated from the aqueous system for easy recycling. The visible-light-controlled
reaction-separation approach provided an efficient way to combine
activity and recovery of metallomicelles in aqueous asymmetric catalysis,
which was a benefit for energy-saving and industrial applications.
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