Chiral octahedral complexes of the form Ir(NHC)<sub>2</sub>(aa)(H)(X) (NHC = N-heterocyclic carbene, aa = chelated amino acid, X = halide) were synthesized by oxidative addition of α-amino acids to iridium(I) bis-NHC precursors and screened for asymmetric transfer hydrogenation of ketones. Following optimization of the reaction conditions, NHC, and amino acid ligands, high enantioselectivity was achieved when employing the Ir(IMe)<sub>2</sub>(L-Pro)(H)(I) catalyst (IMe = 1,3-dimethylimidazol-2-ylidene), which asymmetrically reduces a range of acetophenone derivatives in up to 95% enantiomeric excess. This work illustrates the design of highly enantioselective noble metal catalysts by incorporation of inexpensive "off-the-shelf" chiral amino acids in combination with easily accessible NHC ligands, thus providing an alternative to costly or synthetically challenging chiral ligands.

Design of iridium N-heterocyclic carbene amino acid catalysts for asymmetric transfer hydrogenation of ketones

ACS Spring Meeting 2021

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