The title compound, [Ir 4 (C 5 H 5 N)(CO) 11 ], shows a tetrahedral Ir 4 core in which each Ir atom is linked to three other Ir atoms and three terminal carbonyl groups, except for one Ir atom, which carries two carbonyl ligands and one N-coordinated pyridine molecule. An intricate set of C—H...π hydrogen bonds stabilizes the crystal packing, where the π-systems are those of the C[triple-bond]O bonds of the carbonyl ligands.

Synthesis and catalytic properties of a series of ruthenium carbonyl complexes with 2-substituted pyrazine ligands (pz-R R = Cl, OMe, SMe, CN, NH2) have been studied. Reactions between the [Ru(CO)(3)Cl-2](2) and the pyrazines led mainly to mononuclear compounds of the type [Ru(CO)(3)(R-pz)]. All of these ruthenium pyrazine compounds showed activity in 1-hexene hydroformylation. With an exception of NH2, addition of the substituent to the pyrazine ring was found to improve the catalytic activity compared to the unsubstituted pyrazine. The catalytic cycle was studied by computational DFT methods. The results suggest that the key step in the formation of the active species involves release of one of the carbonyl in the cis position with respect to the pyrazine ring. (c) 2005 Elsevier B.V. All rights reserved.

A series of ruthenium o-phosphane complexes was synthesized and characterized. The reactivity of the prepared complexes was studied by using them as catalysts for the hydroformylation of 1-hexene. The activities depended on the binding mode of the phosphane and on the strength of the ruthenium-phosphane interaction. Strongly coordinated chelating [2-(dimethylamino)phenyl]-(diphenyl) phosphane and [2-(methylthio)phenyl]-(diphenyl) phosphane showed poor activity, while weakly chelated [2-(methoxy)phenyl]-(diphenyl) phosphane and non-chelating phosphanes such as [2-(methyl)phenyl]-(diphenyl) phosphane or [2-(ethyl)phenyl]-(diphenyl) phosphane led to higher activities. (c) 2005 Elsevier B.V. All rights reserved.

Reported here are the in situ FT-IR and 13C-NMR spectroscopic studies of the complex cis-[Ir(CO)2(py)2](PF6 ) (py = pyridine) dissolved in 80% aqueous pyridine used as a precursor in the homogeneous catalysis of the water gas shift reaction (WGSR, CO + H2O AE CO2 + H2). These spectroscopy studies reveal the presence of aminocarbonyliridium complexes with linear and bridging carbonyls groups as reaction intermediates. The WGSR catalysis by Ir4(CO)12 complex dissolved in 80% of aqueous 4-picoline or pyridine under 1.9 atm of CO at 100 C and the FT-IR and 1H-NMR in situ studies of the pyridine promoted disproportionation of Ir4(CO)12, are also described

Iridium complexes Ir-4(CO)(12), IrCl3, and [IrCl(CO)(3)]n show activity toward hydroformylation of 1-hexene in the presence of inorganic salts as promoters. Use of promoters such as LiCl, Li2CO3, KCl, CaCl2, and LiBr enhanced the catalytic activity and aldehyde selectivity considerably by suppressing the competing hydrogenation processes. The activity of the iridium compounds increases in the order IrCl3 < [IrCl(CO)(3)]n < Ir-4(CO)(2). The role of the promoter and the effect of the reaction conditions are discussed. (C) 2003 Elsevier Science (USA). All rights reserved.

Homogeneous catalysts for the water gas shift reaction prepared from Rh2(μ-Pz)2(COD)2 (Pz = pyrazolate ion and COD = 1,5-cyclooctadiene) in aqueous organic solvent media (pyridine, 4-picoline or 2-ethoxyethanol) and Rh2(μ-Pz)2(CO)2(TPPMS)2 (TPPMS = meta-sulfonatophenyl-diphenyldiphosphine) in acidic aqueous media under mild conditions are described. In situ FT-IR, 1H and 13C NMR spectroscopic studies of the Rh2(μ-Pz)2(COD)2 catalytic system reveal the presence of hydrido-Rh complexes with linear and bridging carbonyls. These complexes also catalyze the reduction of nitrobenzene to aniline.