Synthesis and Reactivities of Cp*Ir Amide and Hydride Complexes Bearing C−N Chelate Ligands

Abstract

A series of 16-electron Cp*Ir amide complexes with C−N chelating ligands, Cp*Ir[κ2(N,C)-(NHCR2-2-C6H4)] (2a: R = C6H5, 2b: R = CH3), and the chiral version, Cp*Ir[κ2(N,C)-(R)-{NHCH(CH3)-2-C10H6}] (2e), were obtained in good to excellent yields from reactions of 18-electron iridium amine complexes, Cp*IrCl[κ2(N,C)-(NH2CR2-2-C6H4)] (1a: R = C6H5, 1b: R = CH3) and Cp*IrCl[κ2(N,C)-(R)-{NH2CH(CH3)-2-C10H6}] (1e), with a base. The amido complexes 2 readily reacted with 2-propanol to convert into hydrido(amine) complexes 3 in almost quantitative yields. The chiral amido complex has proven to serve as an efficient catalyst for asymmetric transfer hydrogenation of acetophenone with 2-propanol, giving 1-phenylethanol with a moderate ee. The Brønsted basicity on the metal−NH moiety in the amido complexes was evaluated by deprotonation of acetic acid, dimethyl malonate, and acetone, leading to the corresponding acetato(amine) complex 4 and alkyl(amine) complexes 5 and 6, respectively, indicating that the amido−Ir complexes bearing the C−N chelate have more basic properties than those with N-sulfonylated diamine ligands.