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

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 Co II complex in a CH 2Cl 2/AcOH/nBu 4NBF 4 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. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.