Chiral N,N′-dioxide ligands: synthesis, coordination chemistry and asymmetric catalysis

A class of conformationally flexible ligands composed of a tertiary amino oxide-amide backbone and a straight-chain alkyl spacer was developed. These C-2-symmetric chiral N,N'-dioxide ligands could be straightforwardly synthesized from readily available amino acids and amines. They act as neutral tetra-dentate ligands to bind a wide variety of metal ions. Non-planar cis-alpha M(N,N'-dioxide) complexes enable an intriguing and easily fine-tuned chiral platform for a number of asymmetric reactions. Privileged N,N'-dioxide ligands frequently show wide substrate generality and exceptional levels of stereocontrol for a specific catalytic reaction. We describe approaches to the ligand design and synthesis, structure and bonding in coordination complexes, and the recent developments in asymmetric catalysis.