Iridium(iii)-bis(oxazolinyl)phenyl catalysts for enantioselective C–H functionalization

Abstract

Recently, a small number of diverse iridium complexes have been shown to catalyze unusual atom transfer C–H functionalization reactions. To further our understanding and enhance the utility of iridium complexes for C–H functionalization, we report the design and synthesis of a family of iridium(III)-bis(oxazolinyl)phenyl complexes. The ability to tune the ligand environment around the metal in these systems is exploited to design complexes with the ability to catalyze the asymmetric insertion of donor/acceptor iridium carbenoids into activated C–H bonds. Low catalyst loadings (0.5 mol%) routinely lead to excellent reaction yields (51–99%) and enantioselectivities (83–99%). Density functional theory calculations provide compelling evidence that in these complexes the carbene binds to the iridium cis to the phenyl group of the bis(oxazolinyl)phenyl ligand. This finding is vital for understanding the observed stereochemical induction and is of particular significance in the field of enantioselective transition metal-catalysed atom transfer reactions utilizing oxazoline–X–oxazoline tridentate ligands, as previously employed stereochemical models for these ligand sets are based on the assumption that reactive ligands and Lewis bases bind trans to the central X ligand.