Premium
Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions
Author(s) -
Shen Xiaodong,
Huo Haohua,
Wang Chuanyong,
Zhang Bo,
Harms Klaus,
Meggers Eric
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201500922
Subject(s) - iridium , chemistry , lewis acids and bases , denticity , chirality (physics) , catalysis , chiral lewis acid , enantioselective synthesis , octahedron , medicinal chemistry , metal , stereochemistry , organic chemistry , crystal structure , chiral symmetry breaking , physics , quantum mechanics , nambu–jona lasinio model , quark
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.