Asymmetric Catalysis Using Chiral Salen–Metal Complexes: Recent Advances

Abstract

Chiral salen−metal complexes are among the most versatile asymmetric catalysts and have found utility in fields ranging from materials chemistry to organic synthesis. These complexes are capable of inducing chirality in products formed from a wide variety of chemical processes, often with close to perfect stereoinduction. Salen ligands are tunable for steric as well as electronic properties, and their ability to coordinate a large number of metals gives the derived chiral salen−metal complex very broad utility in asymmetric catalysis. This review primarily summarizes developments in chiral salen−metal catalysis over the last two decades with particular emphasis on those applications of importance in asymmetric synthesis. CONTENTS 1. Introduction and Background 9382 2. Chiral Salen Ligands: Synthesis and Metalation 9382 3. Stereostructural Properties of Chiral Salen−Metal Complexes 9383 4.

Chiral Nanoceramics

“…Chiral ceramic nanostructures for enantioselective catalysis should have nonracemic chiral surface features at the length scale of molecules. Chiral salen-metal complexes, [170] chiral hydrogen-bond donors, [171] chiral metal-organic assemblies, [172] chiral coordination polymers, [173] and different chiral ligands (C 2 -symmetric ligands, N-heterocyclic carbenes, chiral ferrocene, and P-chiral phosphorus ligands, etc.) are widely used for asymmetric catalysis.…”

Asymmetric catalysis in direct nitromethane-free Henry reactions

“…Chiral salen-type ligands have proven useful in a variety of asymmetric metal-catalyzed reactions. 24 In Henry reactions, chiral tetrahydrosalen ([H 4 ]salen) ligands produce strong asymmetry by increasing the basicity and framework exibility of the nitrogen atom. 25 In 2012, White synthesized chiral [H 4 ]salen ligand L5 from cis-2,5-diaminobicyclo[2.2.2]octane (Scheme 13) 26 and used it to conduct a highly enantio-and diastereoselective copper(I)catalyzed Henry reaction.…”

Bioinspired oxidation in cytochrome P450 of isomers orientin and isoorientin using Salen complexes

“…CYP‐bioinspired systems have been used to evaluate in vitro metabolism, generating complementary results to in vivo metabolism studies and thus reducing the number of animals needed at this stage of development. In this field, biomimetic models using metalloporphyrins, which are synthetic catalysts that simulate metabolic reactions with the addition of oxygen donors, have also been applied to natural products because they have a structure similar to the CYP porphyrin iron core …”

“…Subsequently, variation of the binders to the metal gave rise to the generation of novel metalloporphyrins . Although metalloporphyrins are the most suitable catalysts for the CYP enzymatic system, they require high‐cost synthesis and purification, leading researchers to develop other systems, among them the Jacobsen catalyst (Figure C), consisting of Schiff bases coordinated to metal Mn(III) added to tert ‐butyl groups and a cyclohexyl substituent. Since its development, the Jacobsen catalyst has been used to catalyze oxidation reactions including those of non‐functionalized olefins with enantioselectivity and alcohols .…”