Synthesis of Bis(imino)aryl Iridium Pincer Complexes and Demonstration of Catalytic Hydrogen-Transfer Activity

Abstract

Monomeric iridium(III) dihalide complexes containing terdentate bis(imino)aryl ligands, synthesized through oxidative addition of 2-bromoisophthalaldimines RNC(Br)NR (R = Ph 1, Mes 2, i- Pr 3, Me 4 ) to [IrCl(cod)] 2 in the presence of NaBr to form [(RNCNR)IrBr 2 ·solvent] (R = Ph 5, Mes 6, i -Pr 7, Me 8; solvent = MeCN; R = i -Pr 7a; DMSO), are reported. The development of a synthetic route to the complexes is outlined, and full characterization of each member of the series is discussed. X-ray structures for 3 and 4 confirm the retention of the imino groups upon coordination to the metal center. An investigation into the catalytic activity of [(PhNCNPh)IrBr 2 ·MeCN] ( 5 ) as a hydrogen-transfer reagent through the base-catalyzed transfer hydrogenation of ketones (1,3-diphenyl acetone and acetophenone) to alcohols at room temperature was undertaken. Preliminary results indicate that a catalytic species is generated, leading to reasonable conversions at room temperature.