Asymmetric olefin metathesis has great synthetic potential as a result of its versatility in forming C—C bonds under neutral and mild conditions. Stable ruthenium-based catalysts are of special interest because of their ease of handling and their functional-group tolerance. All the chiral ruthenium metathesis catalysts known to date derive from α,α'-disubstituted diamines and therefore have an 3,4-disubstituted N-hetero-cyclic carbene (NHC) ligand (Figure 1). In complexes with monodentate ligands, such as 1 developed by Grubbs as well as in the variants by Collins,the transfer of chirality to the reactive metal center is accomplished through the hindered rotation of N-aryl substituents. In case of the Hoveyda complex 2, which includes bidentate ligands, transfer is accomplished by stereocontrolled substitution of a halogen ligand with a phenol derivative, which has the drawback of significantly lowering the reactivity of the complexes.
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