Asymmetric Hydrogenation of α,β-Unsaturated Nitriles with Base-Activated Iridium N,P Ligand Complexes^†

Although many chiral catalysts are known that allow highly enantioselective hydrogenation of a wide range of olefins, no suitable catalysts for the asymmetric hydrogenation of α,β-unsaturated nitriles have been reported so far. We have found that Ir N,P ligand complexes, which under normal conditions do not show any reactivity towards α,β-unsaturated nitriles, become highly active catalysts upon addition of N,N-diisopropylethylamine. The base-activated catalysts enable conjugate reduction of α,β-unsaturated nitriles with H₂ at low catalyst loadings, affording the corresponding saturated nitriles with high conversion and excellent enantioselectivity. In contrast, alkenes lacking a conjugated cyano group do not react under these conditions, making it possible to selectively reduce the conjugated CC bond of an α,β-unsaturated nitrile, while leaving other types of CC bonds in the molecule intact.