A new concept for catalytic reactions in aqueous media is demonstrated by using a temperature‐responsive polymer support, poly(N‐alkylacrylamide), which is converted into a catalyst by assembly with phosphotungstic acid. At high temperature, the catalyst is highly active in the oxidation of alcohols with H2O2 owing to the formation of emulsions, whereas the product and catalyst are easily separated at low temperature (see scheme).
A switchable catalyst based on temperature change provides a novel solid-phase reaction system in water. An increase in catalyst affinity for organic substrates at higher temperature led to efficient activity driving the solid inner-phase reaction, and loss of affinity at lower temperature allowed easy separation of organic products upon completion of the reaction. Application of this catalyst intelligence to design a novel catalytic system brought about an efficient oxidative cyclization with hydrogen peroxide, a useful method of accessing oxygen heterocycles.
Supported transition‐metal catalysts offer the promise of catalyst reuse in order to make chemical transformations more environmentally friendly and less expensive; however, catalysts that are supported on insoluble scaffolds often exhibit significantly reduced selectivities and rates. A capture/release strategy that unites the benefits of heterogeneous and homogeneous catalysis would overcome these current shortcomings. Herein, we report on a novel capture‐and‐release flow system that takes advantage of a non‐covalent pyrenesingle wall nanotube (SWNT) interaction. We demonstrate that a Pd complex containing one or two pyrene arms is captured and released from a SWNT column at different rates and can be utilized for the homogeneous catalysis of Suzuki and Heck reactions.
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