Chiral Salen Complexes for Asymmetric Heterogeneous Catalysis: Recent Examples for Recycling and Cooperativity

Chiral salen complexes are privileged and versatile catalysts used in a wide variety of enantioselective transformations. Researches for their use in multicatalysis, including cooperative as well as tandem processes, are more recent, but many reports already highlight the important effect of the salen ligand structure on reaction rates and/or selectivities. This review article thus outlines the literature covering last five years, on the current developments of chiral polymetallic salen complexes used in asymmetric heterogeneous catalysis; their preparation, their efficiency as catalysts in various reactions and their recyclability are highlighted according to the immobilization procedures involved for their heterogenization. These methods include grafting on organic or inorganic supports insuring easy recovery by simple filtration. Polymerization processes are also part of recent research, leading to high densities of catalytic sites to favor their cooperativity. Combination of salen complexes via non covalent interactions or their introduction on MOFs and COFs networks is currently in full expansion, with examples of highly functionalized and enantioenriched products issued from tandem catalysis.