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

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)IrBr2·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)IrBr2·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.