Development of Multipurpose Supported Asymmetric Salen Catalysts by Cu(0)-Mediated Reversible Deactivation Radical Copolymerization

Designing heterogeneous catalysts that ensure efficient recycling and reuse of the catalyst in a wide range of transformations remains a real challenge. In this contribution, targeted copolymers are used as support for the development of heterogeneous asymmetric catalysts. They are made up of two methacrylate monomers, 3-azidopropylmethacrylate (AZMA) and 2-methoxyethyl methacrylate (MEMA) used as a diluting agent. Polymerization was carried out using Cu(0)-mediated reversible deactivation radical polymerization (RDRP), yielding two copolymers with controlled MEMA/AZMA compositions of 70/30 and 30/70 with moderate dispersity control (Ð = 1.32–1.54), targeting polymers with a similar molar mass, which is important to achieve precise control of the catalyst loading to implement asymmetric catalysis. The copolymers were post-functionalized using click chemistry with two salen complexes containing a chromium or a cobalt center, these species being recognized for their broad range of applications. The supported catalysts were evaluated in two reactions and recovered by precipitation and filtration techniques. The first reaction involved the asymmetric ring opening (ARO) of cyclohexene oxide with trimethylsilylazide, catalyzed by the chromium sites, the second reaction was the dynamic kinetic resolution (DKR) of epibromohydrin with water, promoted by the cobalt sites. The recycling was effective, demonstrating the robustness and viability of the procedure.