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Electrogenerated Polymers as Efficient and Robust Heterogeneous Catalysts for the Hydrolytic Kinetic Resolution of Terminal Epoxides

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Abstract

Thiophene- and pyrrole-modified chiral cobalt–salen complexes were found to be efficient, enantioselective homogeneous catalysts for the dynamic hydrolytic kinetic resolution (HKR) of epibromohydrin. Their corresponding electrogenerated thiophene–salen–cobalt polymers were prepared by anodic oxidation and could be recovered as insoluble powders for heterogeneous catalysis. Their activity and selectivity were evaluated according to the polymerization conditions. A polymer that was formed from the direct oxidation of a CoII complex in a CH2Cl2/AcOH/nBu4NBF4 electrolytic mixture promoted the most-efficient synthesis of the expected bromoacetal (up to >99 % yield and 87 % ee). This heterogeneous catalyst was easily recovered, could be reused without the need for a reactivation step, and was highly stable, even after 11 consecutive catalytic runs. Moreover, this catalyst was engaged in a multi-substrate recovery procedure with various terminal epoxides, thereby demonstrating its usefulness for the transformation of diverse substrates.

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