title: Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions.
abstract: Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany).
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Shen
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany).
authors.forename: Haohua
authors.initials: H
authors.lastname: Huo
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany).
authors.forename: Chuanyong
authors.initials: C
authors.lastname: Wang
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany).
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany).
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg (Germany). meggers@chemie.uni-marburg.de.|College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, (P. R. China). meggers@chemie.uni-marburg.de.
authors.forename: Eric
authors.initials: E
authors.lastname: Meggers
keywords: Lewis acid; asymmetric catalysis; chiral-at-metal; conjugate addition; iridium