Synthesis and structural determination of the stable dinuclear carbonyl-phosphite rhodium(0) complex: (CO)2(P(O-o-tBuPh)3)Rh-Rh(P(O-o-tBuPh)3)(CO)3

[Rh(μ-OMe)(COD)]₂ reacts with tris-ortho-tert-butylphenylphosphite in the presence of carbon monoxide to provide the first example of a stable dinuclear carbonyl-phosphite rhodium(0) complex with a metal–metal bond distance of 2.73(1) Å. The geometry at the metals is different: square planar and distorted trigonal bipyramid. The crystallographic data indicate that two of the carbonyl ligands are semi-bridged between the two rhodium atoms.     

Interaction of [Rh(2)(O(2)CCH(3))(4)(H(2)O)(2)] and [Rh(2)(O(2)CCH(OH)Ph)(2)(phen)(2)(H(2)O)(2)](O(2)C-CH(OH)Ph)(2) With Sulfhydryl Compounds and Ceruloplasmin

The interaction of binuclear rhodium(II) complexes [Rh(2)(OOCCH(3))(4)(H(2)O)(2)], [Rh(2){OOCCH(OH)Ph}(2)(phen)(2)(H(2)O)(2)] {OOCCH(OH)Ph}(2), [Rh(2)(OOCCH(3))(2)(bpy)(2)(H(2)O)(2)](OOCCH(3))(2) and [Rh(2)Cl(2)(OOCMe)(2)(bpy)(2)](3H(2)O) with ceruloplasmin, cysteine, glutathione and coenzyme A have been investigated using. UV-Vis and CD spectroscopies. The complexes containing phen or bpy at pH = 7.4 and 4.0 are readily reduced with sulfhydryl compounds, while rhodium(II) acetate is relatively stable in these conditions. Complex [Rh(2){OOCCH(OH)Ph}(2)(phen)(2)(H(2)O)(2)] strongly changes structure of ceruloplasmin leading to the decrease of of alpha-helix content and loss of oxidase activity.     

The (NHEt3)[Rh(C6Cl2O4)(CO)2] complex: an example of the adverse counterion influence in the formation of metallic stacks

The synthesis and complete characterisation of the chloroanilato anionic rhodium complexes (NHEt₃)[Rh(C₆Cl₂O₄)(COD)] (1) and (NHEt₃)[Rh(C₆Cl₂O₄)(CO)₂] (2) are reported. In these complexes the chloroanilate dianion chelates the metal through the 1,2 oxygen atoms. The crystal structure of complex (NHEt₃)[Rh(C₆Cl₂O₄)(CO)₂] (2) reveals the adverse influence of the counterion in the formation of metal-columnar stacking. Although the molecules exhibit intermetallic interactions between the planar mononuclear units, the presence of secondary hydrogen bonding between NHEt₃⁺ and the anionic rhodium complexes prevents the formation of an infinite stacked structure.     

Rh(2)(CF(3)CONH)(4): The First Biological Assays of a Rhodium (II) Amidate

The rhodium (II) complexes Rh(2)(tfa)(4).2(tfac) and Rh(2)(tfacam)(4) (tfacam = CF(3)CONH-,tfa = CF(3)COO-,tfac = CF(3)CONH(2)) were synthesized and characterized by microanalysis and electronic and vibrational spectroscopies. Rh(2)(tfacam)(4) was tested both in vitro (U937 and K562 human leukemia cells and Ehrlich ascitic tumor cells) and in vivo for cytostatic activity and lethal dose determination, respectively. This is the first rhodium tetra-amidate to have its biological activity evaluated. The LD(50) value for Rh(2)(tfacam)(4) is of the same order as that of cisplatin, and it was verified that the rhodium complex usually needs lower doses than cisplatin to promote the same inhibitory effects.     

Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2

The organometallics chemical vapour deposition (OM-CVD) technique, using Rh(acac)(CO)₂ as a precursor, was employed for the preparation of heterogeneous Rh catalysts supported on low surface area refractory oxides (α-Al₂O₃, ZrO₂, MgO and La₂O₃). Prepared systems were tested in the methane catalytic partial oxidation (CH₄-CPO) reaction in a fixed bed reactor and compared to a reference catalyst prepared from impregnation of Rh₄(CO)₁₂.Catalysts supported on Al₂O₃, ZrO₂ and MgO show better or comparable performances with respect to the reference system.Complete decomposition of Rh precursor during formation of the metal phase under reductive conditions was investigated by TPRD and confirmed by infrared and mass spectrometry data.Supported Rh phase was characterized by CO and H₂ chemisorption, CO-DRIFT spectroscopy and HRTEM microscopy in fresh and aged selected samples. Rh(I) isolated sites and Rh(0) metal particles were found on fresh catalysts; after ageing an extensive reconstruction occurs mainly consisting in a sintering of Rh isolate sites to metal particles but without large increase in mean particles size.Catalytic performances and Rh species balance were found to be dependent on the support material.     

Hydrogenation of natural rubber latex in the presence of OsHCl(CO)(O2)(PCy3)2

Hydrogenation is an important method of chemical modification, which improves the physical, chemical, and thermal properties of diene elastomers. Natural rubber latex (NRL) can be quantitatively hydrogenated to provide a strictly alternating ethylene–propylene copolymer using a homogeneous osmium catalyst OsHCl(CO)(O₂)(PCy₃)₂. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas‐uptake apparatus. The kinetic results of NRL hydrogenation indicated that this system had a second‐order dependence of the hydrogenation rate on hydrogen pressure and then decreased toward a zero‐order dependence for hydrogen pressures above 13.8 bar. The hydrogenation was also observed to be first‐order with respect to catalyst concentration and inverse first‐order on rubber concentration due to impurities present in the rubber latex. Additions of a controlled amount of acid demonstrated a beneficial effect on the hydrogenation rate of NRL. The temperature dependence of the hydrogenation rate was investigated and an apparent activation energy (over the range of 120–160°C) was calculated as 57.6 kJ/mol. Mechanistic aspects of this catalytic process are discussed on the basis of kinetic results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 640–655, 2006     

Regioselective hydroformylation of vinyl esters catalyzed by Rh(acac)(CO)2 with simple and efficient diphosphinite ligands

Simple and efficient diphosphinite ligands were evaluated in rhodium catalyzed hydroformylation of vinyl acetate. The effect of various reaction variables like temperature, pressure, substrate/Rh ratio, P/Rh ratio, solvents, time and different types of phosphorous ligands were studied. The diphosphinite ligand exhibited a considerable impact on the hydroformylation of vinyl esters and provided good turnover number (up to 10,000) with excellent regioselectivity (99%) to branched aldehyde. Wide range of vinyl esters including long chain aliphatic vinyl esters (up to C18) were well tolerated to provide good to excellent yield of desired product.     

Synthesis,spectral characterization,properties and structure of dinuclear rhenium complex containing bis[4-(2-pyridylmethyleneamino)phenyl]methane ligand

The synthesis, characterization, properties and crystal structure of {(bis[4-(2-pyridylmethyleneamino)phenyl]methane)[Re(CO)₃Br]₂} complex are reported. The ¹H NMR data for this complex shows downfield shift of the bis-diimine ligand protons upon coordination to the Re center. The molecular structure of the dinuclear rhenium(I) complex exhibits distorted octahedral geometries around the each metal center with one Br and facial arrangement of three CO and a cis-bonded diimine ligands. The bis-diimine ligand, twists via a half-turn around the metal–metal axis. Electrochemical investigation reveals two oxidation waves and two irreversible reduction waves.     

A novel dianionic seven-coordinate complex of tungsten(II), [WCl3(GeCl3)(CO)3]2−: Synthesis,spectroscopic properties and X-ray crystal structure

A new dianionic complex of tungsten(II), [(WCl₃(GeCl₃)(CO)₃]²⁻ (1²⁻), containing the piperidinium cations [Hpip]⁺ as the counter ions, has been obtained from the reaction between [W(CO)₄(pip)₂] and GeCl₄ in dichloromethane solution, and its molecular structure has been elucidated by single-crystal X-ray diffraction studies. The chemical properties of complex 1 were investigated by IR and NMR spectroscopy in solution.     

Selectivity of the OsHCl(CO)(O2)(PCy3)2 catalyzed hydrogenation of nitrile–butadiene rubber

A new homogeneous catalyst precursor has been discovered for the hydrogenation of carbon–carbon unsaturation resident within acrylonitrile–butadiene copolymers. The hydrido‐phosphine complex OsHCl(CO)(O₂)(PCy₃)₂ (1) selectively and quantitatively saturates olefin, leaving the copolymer's nitrile functionality intact. However, the process suffers from an undesirable crosslinking reaction that is not demonstrated by the established rhodium technology. The extent of this crosslinking is dependent on the process conditions and can be minimized by operating with a low catalyst concentration and high H₂ pressure. Kinetic studies have identified a previously unknown unexpected influence of olefin on the polymer crosslinking process. In light of this new information, the prevailing mechanism for this class of reactions has been reconsidered. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1618–1626, 2001     

Hydrogenation of natural rubber in the presence of OsHCL(CO)(O2)(PCY3)2: Kinetics and mechanism

The homogeneous catalyst precursor, OsHCl(CO)(O₂)(PCy₃)₂, was utilized for the hydrogenation of natural rubber to convert the unsaturated structure to a saturated form, providing an alternating ethylene‐propylene copolymer. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas‐uptake apparatus. ¹H NMR spectroscopy was used to determine the final olefin conversion to the hydrogenated product. Kinetic data, collected according to a statistical design framework, defined the influence of catalyst and polymer concentration, hydrogen pressure, and reaction temperature on the catalytic activity. The kinetic results indicated that the hydrogenation rate exhibited a first‐ shifted to zero‐order dependence on hydrogen at lower hydrogen pressure, which then decreased toward an inverse behavior at pressures higher than 41.4 bar. The hydrogenation was also observed to be first‐order with respect to catalyst concentration, and an apparent inverse dependence on rubber concentration was observed due to the impurities in the rubber. The hydrogenation rate was dependent on reaction temperature, and the apparent activation energy over the temperature range of 125–145°C was found to be 122.76 kJ/mol. Mechanistic aspects of the hydrogenation of natural rubber in the presence of OsHCl(CO)(O₂)(PCy₃)₂ were proposed on the basis of the observed kinetic results. The addition of some acids and certain nitrogen containing materials showed an effect on the hydrogenation rate. The thermal properties of hydrogenated natural rubber indicated that the thermal stability increased with increasing % hydrogenation of the rubber. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4499–4514, 2006     

Thermal decomposition products of the heteronuclear complex,LaNi(dhbaen)(NO3)(H2O)n

The heteronuclear LaNi(dhbaen)(NO₃)(H₂O)_n complex was synthesized and its thermal decomposition products were analyzed by differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, Auger electron spectroscopy (AES) with scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Hexagonal perovskite-type LaNiO₃ having fine particle size was obtained by sintering at 600 °C. AES showed that the elemental distributions of La, Ni, and O on the surface were very homogeneous for the sample decomposed at 900 °C. The LaNiO₃ decomposed to La₃Ni₂O₇ and NiO when the heating temperature increases up to 1000 °C. Heteronuclear LnNi(dhbaen)(NO₃)(H₂O)_n complexes (with Ln=Pr, Nd, Sm, and Gd) were also synthesized. The perovskite-type LnNiO₃ phase could not be formed by their thermal decomposition.     

Hydrogenation of cis‐1,4‐poly(isoprene) catalyzed by OsHCl(CO)(O2)(PCy3)2

The quantitative hydrogenation of cis‐1,4‐poly(isoprene) (CPIP) provides an easy entry to the alternating copolymer of ethylene–propylene, which is difficult to prepare by conventional polymerization. The homogeneous hydrogenation of CPIP, in the presence of OsHCl(CO)(O₂)(PCy₃)₂ as catalyst, has been studied by monitoring the amount of hydrogen consumed during the reaction. The final degree of olefin conversion measured by computer‐controlled gas uptake apparatus was confirmed by infrared spectroscopy and ¹H nuclear magnetic resonance analysis. Kinetic experiments for CPIP hydrogenation in toluene solvent indicate that the hydrogenation rate is first order with respect to catalyst and carbon–carbon double bond concentration. A second‐order dependence on hydrogen concentration for low values and a zero‐order dependence for higher values of the hydrogen concentration was observed. The apparent activation energy for the hydrogenation of CPIP over the temperature range of 115–140°C was 109.3 kJ/mole. Mechanistic aspects of this catalytic process are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 142–152, 2003     

Synthesis,structure, and properties of dinuclear copper (II) complex with a (H2O)12 cluster

A novel pyrazole complex, namely [Cu₂(4,4′-bpy)₂(2,2′-bpy)(L)₂]·6H₂O has been synthesized under mild condition (4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine). We report the structural evidence in the solid state of discrete water hexamers chair-like conformation. These units were found to act as supramolecular glue in the aggregation of dinuclear copper (II) complex to give a three dimensional network through hydrogen-bonding. The preliminary investigation on the electrochemical property and fluorescence property of the complex are presented.     

A dinuclear zinc(II) complex of 2,6-bis[((2-hydroxybenzyl)(2-pyridylmethyl)amino)methyl]-4-methylphenol derived from bis(acetylacetonato)zinc(II)

Reaction of the symmetrical proligand H₃L with bis(acetylacetonato)zinc(II) has given the homodinuclear complex [Zn₂L(acac)]·CH₃CN in which one of the pendant phenolato groups functions as a bridge for the dinuclear zinc centre. The complex crystallises in the triclinic space group P-1, with unit cell parameters a=10.0250(11) Å, b=10.6132(13) Å, c=19.139(2) Å, α=80.418(2)°, β=75.792(2)°, γ=84.532(2)°.     

Immobilization of HRh(CO)(P(m-C6H4SO3Na)3)3 on an anion exchange resin for the hydroformylation of higher olefins

The anion exchange resin Amberlyst, A-26, forms an efficient matrix for the immobilization of the water soluble complex, HRh(CO)(m-C₆H₄SO₃Na)₃)₃. Catalysis proceeds in anhydrous alcohol solvents which allows the conversion of water insoluble olefins to aldehydes. Activities and selectivities are similar to both supported aqueous phase catalysts and to the neutral complex, HRh(CO)(PPh₃)₃ in non-aqueous solvents. The catalyst preparation minimizes the quantity of water in the supported catalyst; the lack of water is thought to be responsible for an increase in catalyst stability toward oxidation.     

Support effects in the dissociation of CO on Rh/CeO2(111)

The adsorption and reaction of CO on Rh particles supported on stoichiometric and partially reduced CeO₂(111) surfaces was studied using a combination of HREELS and TPD. A fraction of the CO adsorbed on the supported Rh particles was found to undergo dissociation to produce adsorbed C and O atoms. TPD results for isotopically labeled CO demonstrated that O atoms produced by CO dissociation rapidly exchange with the oxygen in the ceria lattice. The fraction of adsorbed CO which dissociated was found to increase significantly with the extent of reduction of the CeO₂(111) surface, suggesting that oxygen vacancies on the surface of the support play a direct role in the CO dissociation reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,structure and properties of the mixed-ligand tungsten(II) complex [WBr2(CO)3(tmpymt)] (tmpymt = 1,4,6-trimethylpyrimidine-2-thione)

The reaction of [{WBr(CO)₄}₂(μ-Br)₂]₂ 1 with 1,4,6-trimethylpyrimidine-2-thione (tmpymt) affords the air-sensitive complex [WBr₂(CO)₃(tmpymt)] 2. The X-ray structure of 2·C₃H₆O reveals that the geometry surrounding the tungsten(II) atom is best described as a distorted capped trigonal prism with a bromine atom Br(1) in the unique capping position. The other bromine atom Br(2), the (N,S)-chelate and one carbonyl C(41) occupy the capped quadrilateral face. The complex has been additionally characterized by IR and NMR spectroscopy. The optimized molecular structure (RHF/LanL2DZ) supports the experimental data.     

Synthesis and Anti-Candida Activity of Cobalt(II) Complexes of Benzene-1,2-Dioxyacetic Acid (bdoaH(2)). X-Ray Crystal Structures of [Co(bdoa)(H(2)O)(3)] 3.5H(2)O and {[CO(phen)(3)](bdoa)}(2)24H(2)O (phen = 1,10-Phenanthroline)

Co(CH(3)CO(2))(2)4H(2)O reacts with benzene-1,2-dioxyacetic acid (bdoaH(2)) to give the Co(2+) complexes [Co(bdoa)(H(2)O)(3)]H(2)O (1a) and [Co(bdoa)(H(2)O)(3)] 3.5H(2)O (1b). Subsequent reaction of 1a with 1,10- phenanthroline produces [CO(phen)(3)] bdoa10H(2)O (2a) and {[CO(phen)(3)](bdoa)}(2)24H(2)O (2b). Molecular structures of 1b and 2b were determined crystallographically. In 1b the bdoa(2-)- ligates the metal by two carboxylate oxygens and two ethereal oxygens, whereas in 2b the bdoa(2-) is uncoordinated. The Mn(2+) and Cu(2+) complexes [Mn(bdoa)(phen)(2)]H(2)O (3) and [Cu(pdoa)(imid)(2)] (4) were also synthesised, 1a-4 and other metal complexes of bdoa H(2) (metal = Mn(2+), Co(2+) ,Cu(2+), Cu(+) ) were screened for their ability to inhibit the growth ofhe yeast Candida albicans. Complexes incorporating the 1,10-phenanthroline ligand were the most active.