Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions |
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| Authors: | Xiaodong Shen Haohua Huo Chuanyong Wang Bo Zhang Dr Klaus Harms Prof?Dr Eric Meggers |
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| Affiliation: | 1. Fachbereich Chemie, Philipps‐Universit?t Marburg, Hans‐Meerwein‐Stra?e, 35043 Marburg (Germany);2. College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, (P. R. China) |
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| 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. |
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| Keywords: | asymmetric catalysis chiral‐at‐metal conjugate addition iridium Lewis acid |
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