Chiral N-heterocyclic carbene iridium catalyst for the enantioselective hydrosilane reduction of ketones

Abstract

Enantioselective reduction of ketones with (EtO)2MeSiH catalyzed by an in-situ generated N-heterocyclic carbene (NHC) Ir complex at room temperature has been developed. A series of benzimidazolium salts were synthesized and screened in the asymmetric hydrosilylation reaction. As a result, propiophenone was efficiently reduced by the combined catalytic system of [IrCl(cod)]2 and NHC–Ag complex derived from N-(1-naphthalenylmethyl)-substituted benzimidazolium salt L12, affording the corresponding alcohol in 92% yield and with 92% ee. Moreover, the evaluation of an Ir catalyst precursor showed that cationic [Ir(cod)2]BF4 complex could be used. Furthermore, the introduction of a chiral hydroxyamide side arm into the benzimidazolium salt was critical for the successful design of the NHC ligand.