Five iridium complexes containing bidentate phosphine ligands, IrH(CO)(PPh3)(BPPB) [BPPB = 1,2-bis(diphenylphosphino)benzene] (1), IrH(CO)(PPh3)(BISBI) [BISBI = 2,2'-bis(diphenylphosphinomethyl)-1,1'-biphenyl] (2), IrH(CO) (PPh3)(BDNA) [BDNA = 1,8-bis(diphenylphosphinomethyl)naphthalene] (3), IrH(CO)(PPh3)(BDPX) [BDPX = 1,2-bis(diphenylphosphinomethyl)benzene] (4), and IrHCl(CO)(PCP) [PCP-H = 1,3-bis(diphenylphosphinomethyl)benzene] (5) were synthesized. Their compositions and structures were identified by elemental analysis, FTIR, P-31{H-1} NMR and H-1 NMR. The molecular structure of IrH(CO)(PPh3)(BDNA) determined by single crystal X-ray diffraction indicated a trigonal bipyramidal structure with the three phosphorus atoms in the equatorial plane. The crystal belonged to triclinic system, P1 space group, a = 11.47 Angstrom, b = 11.65 Angstrom, c = 19.20 Angstrom, alpha = 8 1.95degrees, beta = 75.60degrees, gamma = 70.60degrees, and Z = 2. The catalytic hydrogenation activities and selectivities of the five complexes as catalysts for citral and cinnamaldehyde were investigated. Complexes 1-4 showed high selectivity for the hydrogenation of C=O group in citral. High selectivity for the hydrogenation of C=O group in cinnamaldehyde catalyzed by complex 4 could be obtained in the presence of excess amount of ligand (BDPX). (C) 2002 Elsevier Science B.V. All rights reserved.