Asymmetric Hydrogenation of Imines Using NHC‐Phosphine Iridium Complexes

The asymmetric hydrogenation of imines catalyzed by N-Heterocyclic carbene-phosphine iridium complexes is described. The hydrogenation proceeded smoothly under balloon pressure of hydrogen gas giving the amines in up to 91% ee. Mechanistic experiments indicated that both a direct hydrogenation pathway and a transfer hydrogenation pathway are plausible for the hydrogenation.

Abstract

α-Chiral amines represent a frequently observed functional group in pharmaceuticals. Here, the synthesis of such motifs (up to 91% ee) is described by asymmetric hydrogenation of imines catalyzed by NHC,P-iridium complexes. The hydrogenation proceeded smoothly, even under balloon pressure of hydrogen atmosphere. Mechanistic experiments indicated that the reduction most likely advances by a combination of direct hydrogenation and a hydrogen transfer process using either H₂ or iPrOH as the reductant, respectively.

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