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Hafedh, N., Favereau, L., Caytan, E., Roisnel, T., Jean, M., Vanthuyne, N., Aloui, F. and Crassous, J. (2019) Synthesis and Chiroptical Properties of Organometallic Complexes of Helicenic N-Heterocyclic Carbenes. Chirality, 31, 1005-1013.
https://doi.org/10.1002/chir.23143

has been cited by the following article:

• TITLE: Operationally Simple Enantioselective Silane Reduction of Ketones by the [Ir(OMe)(cod)]2/Azolium Catalytic System

  AUTHORS: Satoshi Sakaguchi, Chika Nagao, Ryo Ichihara, Shogo Matsuo

  KEYWORDS: Asymmetric Catalysis, Enantioselective Reduction, Hydrosilylation Reaction, N-Heterocyclic Carbene, Iridium

  JOURNAL NAME: International Journal of Organic Chemistry, Vol.14 No.1, February 28, 2024

  ABSTRACT: An operationally simple protocol was designed for the enantioselective silane reduction (ESR) of ketones using air- and moisture-stable [Ir(OMe)(cod)]2 (cod = 1,5-cyclooctadiene) (3) as a metal catalyst precursor. This reaction was driven by chiral hydroxyamide-functionalized azolium salt 2. The catalytic ESR reaction could be performed under benchtop conditions at room temperature. Treatment of 2 with 3 in THF yielded the monodentate IrCl(NHC)(cod) (NHC = N-heterocyclic carbene) complex 4 in 93% yield, herein the anionic methoxy ligand of 3 serves as an internal base that deprotonates the azolium ring of 2. The well-defined Ir complex 4 catalyzed the ESR reaction of propiophenone (6) with (EtO)2MeSiH using the pre-mixing reaction procedure. Based on this success, the catalytic ESR reaction was designed and implemented using an in situ-generated NHC/Ir catalyst derived from 2 and 3. Thus, a wide variety of aryl ketones could be reduced to the corresponding optically active alcohols in moderate to excellent stereoselectivities at room temperature without temperature control. Since the high catalytic activity of 3 was observed, we next evaluated several other transition metal catalyst precursors for the catalytic ESR reaction under the influence of 2. This evaluation revealed that Ir(acac)(cod) (acac = acetylacetonate) (28) and [IrCl(cod)]2 (5) can be successfully used as metal catalyst precursors in the ESR reaction.