Chem. 1960, 25, 1807-1808 and references cited therein. (2) A catalytic amount of impurity in chromium(I1) salt played an important role in the following reaction. (a) Takai, K.; Tagashira, M.; Kuroda, T.; Oshima, K.; Utimoto, K.; Nozaki, H.

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.

Tantalum-alkyne complexes with the general formula TaCl3(R1C⋮CR2)(dme) (1a, R1 = R2 = Et; 1b, R1 = R2 = n-C5H11; 1c, R1 = Ph, R2 = Me; 1d, R1 = R2 = Ph; DME = 1,2-dimethoxyethane) were synthesized by treatment of the corresponding alkynes with a low-valent tantalum derived by reduction of tantalum pentachloride with zinc powder in a mixed solvent of toluene and DME. The DME ligand can be replaced by 2 equiv of pyridine to afford the corresponding dipyridine complexes TaCl3(R1C⋮CR2)(py)2 (2a, R1 = R2 = Et; 2b, R1 = R2 = n-C5H11; 2c, R1 = Ph, R2 = Me; 2d, R1 = R2 = Ph). Additionally, the reaction of 1a with the bidentate nitrogen ligands bipyridine and N,N,N‘,N‘-tetramethyethylenediamine (= TMEDA) gave TaCl3(EtC⋮CEt)(bipy) (3) and TaCl3(EtC⋮CEt)(tmeda) (4), respectively. The η2- and 4e-coordination mode of an alkyne with a large contribution of a metalacyclopropene canonical structure was revealed by spectroscopic methods (NMR and IR) and crystallographic analyses of 1a, 1c, 2a, and 4. The reactivies of the tantalum-3-hexyne complexes 1a, 2a, 3, and 4 toward 3-phenylpropanal were investigated. Only the pyridine complex 2a reacted with a stoichiometric amount of the aldehyde to afford the corresponding allylic alcohol in 77% yield upon hydrolysis. The reaction proceeded via an oxatantalacyclopentene species.