Mononuclear iridium(III) complexes of general formula IrX(H)(O2CR)[(S)-binap] (2, R = CH3; 3,
R = Ph; 4, R = C6H4CH3-p; a, X = Cl; b, X = Br; c, X = I) were prepared by one-pot reaction of
[Ir(μ-X)(cod)]2 with 2 equiv of (S)-BINAP [=2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl] and an excess
of the corresponding carboxylic acid in toluene. The structure of (S)-2−4 bearing an (S)-BINAP was
confirmed to be OC-6−23-A (Λ-conformation) by X-ray analysis of (S)-4a−c. In this reaction, the iridium(I) complex {Ir(μ-Cl)[(S)-binap]}2 [(S)-5a] and pentacoordinated iridium(I) complexes IrX(cod)[(S)-binap]
[(S)-7b, X = Br; (S)-7c, X = I] were generated prior to the oxidative addition of carboxylic acid. Cationic
dinuclear iridium(III) complexes of general formula [{Ir(H)[(S)-binap]}2(μ-X)3]X [(S)-8: a, X = Cl; b,
X = Br; c, X = I] were prepared, and their cationic bifacial octahedral dinuclear structure was characterized
by spectral data and combustion analysis. The anionic portion of these complexes could be replaced by
NaPF6, leading to the corresponding PF6 salts [{Ir(H)[(S)-binap]}2(μ-X)3]PF6 [(S)-8: d, X = Cl; e, X =
Br; f, X = I]. Iodo-acetate complexes of p-TolBINAP (=2,2‘-bis(di-4-tolylphosphino)-1,1‘-binaphthyl)
[(S)-9c] and SYNPHOS [=2,2‘,3,3‘-tetrahydro(5,5‘-bi-1,4-benzodioxin)-6,6‘-diyl]bis(diphenylphosphine)]
[(S)-10c] were also prepared according to the method used for the BINAP complex (S)-2c and were
characterized spectroscopically. Cationic dinuclear complexes of p-TolBINAP [(S)-11c] and SYNPHOS
[(S)-12c] were also generated. Using these complexes, the effect of halide variation was studied by
asymmetric hydrogenation of 2-phenylpyrrolidine (13) and 2-phenyl-4,5,6,7-tetrahydro-3H-azepine (15)
along with 2-phenylquinoline (16), and the results indicated that iodide complexes were better catalyst
precursors for catalytic activity than the corresponding chloride and bromide complexes, but were not
superior in enantioselectivity.
