Cationic half-sandwich C-N chelating Ir and Rh complexes [Cp*M(NCCH3){kappa(2)(N,C)-NH2CR2-2-C6H4}]+SbF6- (1a, M = Ir, R = CH3; 1b, M = Ir, R = C6H5; 2a, M = Rh, R = CH3; 2b, M = Rh, R = C6H5) are synthesized by AgSbF6-mediated halide abstraction from neutral azametallacycles derived from tritylamine or cumylamine and are fully characterized by NMR spectroscopy and X-ray crystallography. The treatment of the cationic complex 1b with H-2 gas under ambient conditions in the presence of triethylamine in THF-d(8) quantitatively yielded hydrido(amine) complex [Cp*Ir(H){kappa(2)(N,C)-NH2C(C6H5)(2)-2-C6H4}] (4). The C-N chelating Ir complex shows a higher catalytic activity than an N-N chelating complex, [Cp*Ir(NCCH3)(Tscydn)+SbF6- (3; Tscydn = N-(p-toluenesulfonyl)-1,2-cyclohexanediamime), that has been previously used for the asymmetric hydrogenation of acyclic imines. For example, the cationic Ir complex la promoted the hydrogenation of N-(1-phenylethylidene)benzylamine under 30 atm at 30 degrees C in the presence of excess AgSbF6 to produce the corresponding amine in 97% yield within 2 h. The cationic Rh complexes 2 serve as efficient catalysts for hydrogenative condensation of nitriles in the presence of AgSbF6, producing dibenzylamines selectively even at 60 degrees C.
A series of 16-electron Cp*Ir amide complexes with C-N chelating ligands, Cp*Ir[kappa(2)(NC)-(NHCR2-2-C6H4)] (2a: R = C6H5, 2b: R = CH3) and the chiral version, Cp*Ir[kappa(2)(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[kappa(2)(N,C)-(NH2CR2-2-C6H4)] (1a: R = C6H5, 1b: R = CH3) and Cp*IrCl[kappa(2)(N,C)-(R)-NH2CH(CH3)-2-C10H6}] (le), 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 Bronsted 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.