Catalytic hydrogenation of soybean oil with Rh(l) dihydride complexes as catalysts

Cationic rhodium(I) complexes of the type [NBD Rh L₂]⁺[C1O₄]⁻ (NBD = norbornadiene and L = diphenylphosphinoethane or triphenylphosphine) have been studied as catalysts for the hydrogenation of soybean oil. These catalysts give a good yield of products with cis-configuration. Indeed, hydrogenation could be performed under mild conditions (30 C, 1 atm hydrogen pressure) to an iodine value of 80 with not more than 12% oftrans monoenes and only 5% conjugated isomers formed. The results obtained are interpreted on the basis of the equilibrium H₂RhL _n ⁺ ⇌HRhL_n+H⁺. By the addition of acid (HClO₄ ) the bishydrido form of the catalyst could be studied. With this system only small amounts of trans monoenes were formed and no othertrans isomers could be detected. By the addition of a base such as triethylamine, the monohydridic form of the catalyst could be studied. In contrast to the bishydrido complex, this system gave large amounts oftrans monoenes, together withcis-trans andtrans-trans forms of the 18:2 acid. With both forms of the catalyst system, conjugated isomers were formed.     

Rhodium complexes containing chiral P-donor ligands as catalysts for asymmetric hydrogenation in non conventional media

Abstract  

Rhodium-catalysed asymmetric hydrogenation using P-donor ligands, such as new fluorinated (R)-BINOL and azadioxaphosphabicyclo[3.3.0]octane derivatives was carried out in different reaction media such as organic solvent (CH₂Cl₂), ionic liquid ([BMI][PF₆]), supercritical carbon dioxide (scCO₂) and [BMI][PF₆]/scCO₂ mixture. The best enantioselectivities were obtained in neat [BMI][PF₆], allowing a recycling up to ten times without activity loss. However, the enantioselectivity was lost due to ligand leaching. The ionic liquid phase containing rhodium molecular species was supported on functionalized multi-walled carbon nanotubes in order to improve the recycling, but unfortunately the asymmetric induction was lost upon catalyst immobilization.     

C,N-chelated dicyclopentadienylzirconium complexes and their possible use as hydrogenation catalysts

In situ generated Cp₂Zr(n-Bu)Cl (6) reacts with {2-[(CH₃)₂NCH₂]C₆H₄}₂Pb to form exclusively {2-[(CH₃)₂NCH₂]C₆H₄}Cp₂ZrCl (7), [(CH₃)₂NCH₂]C₆H₅, butene and elemental lead. The further derivatization of chloride (7) to fluoride (8), hydride (9), methyl derivative (10), and a reduction of 7 are also described. The crystal structures of 7–10 were determined. The catalytic activity of 9 and 10 in hydrogenation of styrene was also preliminarily tested.     

1,3,5-Triaza-7-phosphaadamantane (PTA) ligated iridium(I) complexes as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine in water

The water-soluble complex [Ir(COD)(PTA)₃]Cl (1, PTA = 1,3,5-triaza-7-phosphaadamantane) was prepared by the reaction of [IrCl(COD)]₂ with six equivalents of PTA under a nitrogen atmosphere. Compound 1 was fully characterized in solution and the solid state. 1 crystallized in the monoclinic space group C2/c with a = 29.648(9) Å, b = 11.238(2) Å, c = 19.930(2) Å, and β = 96.55(2)°. Complex 1 and the related Ir(I) compounds, [IrCl(CO)(PTA)₃] (2) and [Ir(CO)(PTA)₄]Cl (3), were active catalysts in the intramolecular hydroamination of 4-pentyn-1-amine in water. This is the first reported study of the Ir(I) mediated transformation in aqueous media.     

Hydrogenation of soybean oil with cationic Rh(I)-Phosphine complexes as catalysts — Para-toluene sulfonate and sulfonated styrene resins as counterions

A cationic rhodium(I) complex, viz. Rh NBD diphos⁺ 4-CH₃-C₆H₅SO ₃ ⁻ [NBD = norbornadiene, diphos = (C₆H₅)₂ P-CH₂-CH₂-P(C₆H₅)₂], has been used as a homogeneous catalyst for the hydrogenation of soybean oil in acetone solution. This complex acts almost in the same way as the corresponding ones with ClO ₄ ⁻ or PF ₆ ⁻ as conuterions, i.e., it gives high polyene selectivity and low formation oftrans isomers. Because of the somewhat stronger basic character of the p-toluene-sulfonate ion compared with the perchlorate and hexafluorphosphate ions, the relative proportion of reaction via the so-called monohydride path is larger in the present case. When the ionic complex, Rh NBD diphos⁺, is bound to a solid support, e.g., to the anionic sites of sulfonated polystyrene resins, a nearly total lack of catalytic activity is observed. Possible reasons for these effects are discussed-in terms of π-arene-metal binding and covalent coordination of the sulfonate group.     

O.N-bis(diphenylphosphino) derivatives of chiral trans- and cis-2-aminocyclohexanols: Synthesis and enantioselective behaviour as ligands in Rh-based homogeneous hydrogenation catalysts

trans- and cis-2-Methylamino cyclohexanols (MAC) were prepared in enantiomerically pure forms and transformed into O.N-bis(diphenylphosphino) derivatives (“PONP”). An analogous trans-1 R; 2 R-aminocyclohexanol PONP could only be isolated in an impure form, whereas the attempted synthesis of PONP's of diastereoisomeric trans-2-(N-α-phenylethylamino)-cyclohexanols failed. Cationic Rh(I)-chelates of the new PONP's catalyzed the enantioselective hydrogenation of dehydro-α-acylamino acids with ≦97% ee. A comparison of the enantiodiscriminating properties of the MAC-PONP's with structurally related chiral ligands leads to surprising conclusions.     

Photo-activated metal carbonyl complexes as stereoselective catalysts for the homogeneous hydrogenation of dienes

Significantly increased activity of Cr(CO)₆ was achieved for the stereoselective homogeneous hydrogenation of methyl sorbate andtrans,trans-conjugated fatty esters at ambient temperature and pressure by exposing the catalyst to UV irradiation (3500 Å) in a solvent mixture of cyclohexane-acetonitrile (20:1). In this solvent mixture, methyl sorbate was converted quantitatively at ambient conditions into methylcis-3-hexenoate, and methyltrans-9,trans-11-octadecadienoate into methylcis-10-octadecenoate (99.9%). These products are expected by 1,4-addition of hydrogen. Under these conditions no hydrogenation of methyl linoleate occurred. Under the same conditions, cycloheptatriene-Cr(CO)₃ showed lower activity than Cr(CO)₆, and Mo(CO)₆ and mesitylene-Mo(CO)₃ showed no significant activity toward conjugated substrates. When Cr(CO)₆ and Mo(CO)₆ were irradiated at 2537 Å they caused the geometric isomerization of methyl sorbate without hydrogenation, but had no effect on methyl linoleate. A hydrogenation mechanism is proposed for Cr(CO)₆ that involves CH₃CN- and H₂-Cr(CO)₃ complexes as intermediates for the stereoselective 1,4-addition of hydrogen totrans,trans-conjugated dienes.     

Amino acid derived amides and hydroxamic acids as ligands for asymmetric transfer hydrogenation in aqueous media

Amides and hydroxamic acids derived from α-amino acids were evaluated as ligands in combination with rhodium and iridium half-sandwich complexes in asymmetric transfer hydrogenation (ATH) of ketones. The reactions were performed in aqueous media using lithium formate as hydride source. The catalyst systems turned out to be highly efficient and ee's up to 90% were obtained.     

Electronic interactions in copper(I) and silver(I) complexes between the ligands and metals as evidenced with cyclic voltammetry

The electronic interaction between datively bonded phosphanes, 2,2′-bipyridine and 1,10-phenanthroline ligands, and copper(I) and silver(I) ions has been studied with cyclic voltammetry. Based on the shifts of reduction potentials of the metals, various degrees of interactions have been identified. They are correlated with the type and molecular structure of the bridging ligand.     

Graphitic mesoporous carbon as a support of promoted Rh catalysts for hydrogenation of carbon monoxide to ethanol

Graphitic mesoporous carbon (GMC), prepared through high-temperature graphitization of soft-templated amorphous mesoporous carbon (AMC), was used as the support for Mn, Li, and Fe triple-promoted Rh catalysts for CO hydrogenation to ethanol. The use of GMC results in C₂H₅OH selectivity and formation rate comparable to nonporous SiO₂ support along with a significant inhibition on the formation of undesired CH₄ and light hydrocarbons at the expense of appreciable amounts of CO₂ produced. The better catalytic performance of promoted-Rh/GMC than those supported on other carbon allotropes (AMC and non-porous graphitic carbon black) seems to be associated with the specific graphitic structure and mesoporosity of GMC. The surface modification of GMC by wet oxidation leads to considerable increases in C₂H₅OH selectivity and formation rate. The modified GMC as a support shows substantially greater CO₂-free selectivity for C₂H₅OH than the SiO₂.     

Cyclohexene hydrogenation using Group VIII metal complexes as catalysts in heterogeneous and homogeneous conditions

The stability and catalytic behaviour of a ruthenium complex with chloride and tridecylamine as ligands were studied. The hydrogenation of cyclohexene carried out in mild conditions, both in homogeneous and heterogeneous conditions, was used as a test reaction. FTIR and XPS results show that the active species is the complex itself, which is stable under the reaction conditions. XPS determination shows that the ruthenium complex is tetra‐coordinated, suggesting that its formula is [RuCl₂(NH₂(CH₂)₁₂CH₃)₂]. This ruthenium complex supported on γ‐Al₂O₃ is more active and sulfur‐resistant than the same complex unsupported and even more than a nickel complex with the above mentioned ligands. The Ru complex, supported or not, is also more active and sulfur‐resistant than a conventional Ru/γ‐Al₂O₃ catalyst evaluated in the same operational conditions. © 2001 Society of Chemical Industry     

A hydrophilic chiral diamine from d-glucose in the Rh(I) catalysed asymmetric hydrogenation of acetophenone

A strategy for the synthesis of a new hydrophilic chiral diamine derived from α-d-glucose is described. The compound is obtained by introducing proper nitrogen functions at C2 and C3 positions of the sugar ring, and by deprotecting positions 4 and 6. The efficiency of the ligand in the Rh(I)-catalysed hydrogenation of acetophenone has been examined by using isopropanol and ethanol as hydrogen sources. The secondary alcohol has been obtained in ees up to 50%.     

Recyclable plant tannin‐chelated Rh(III) complex catalysts for aqueous–organic biphasic hydrogenation of quinoline

BACKGROUND: Synthetic ligands have conventionally been used for the preparation of homogenous Rh complex catalyst but biomass has rarely been utilized for this purpose. In the present investigation, plant tannins (natural polyphenols) were used as water‐soluble ligands for the preparation of homogenous Rh³⁺ complex catalysts. RESULTS: Based on X‐ray photoelectron spectroscopy (XPS) and proton nuclear magnetic resonance (HNMR) analyses, the preparation mechanism of these complex catalysts was proven to involve chelating interactions between Rh³⁺ and the adjacent phenolic hydroxyls of plant tannins. As a result, the use of plant tannin promoted aqueous‐organic biphasic interactions and the plant tannin‐chelated Rh³⁺ complex catalysts exhibited much higher catalytic activity than commercial Rh complex catalysts in the biphasic hydrogenation of quinoline. Furthermore, the plant tannin‐chelated Rh³⁺ complex can be reused three times without significant loss of catalytic activity CONCLUSION: Our experimental results suggested that black wattle tannin (BWT) can be used as water‐soluble ligands for the preparation of highly active and recyclable Rh³⁺ complex catalysts. Copyright © 2012 Society of Chemical Industry     

Polymer-metal complexes,based on poly(itaconic acid ester) derivatives,as catalysts for the decomposition of hydrogen peroxide

Poly(methyl itaconates) and poly(heptyl itaconates), modified with ethylene diamine (EN) and tetraethylene pentamine (TETRAEN) side chains, were complexed with cobalt and copper ions, and their efficiencies as catalysts for the decomposition of hydrogen peroxide were assessed. All the polymer complexes studied were found to be active catalysts, but it was observed that the polymers with TETRAEN side chain, when complexed with CoCl₂ and CuCl₂ were less efficient than polymers with EN side chains which were complexed with trans-dichlorobis(ethylenediamine) cobalt(III) chloride, trans-[Co(EN)₂Cl₂]Cl. One feature of interest was that when the alkyl side chain of the poly itaconate was heptyl the rate of decomposition of hydrogen peroxide was faster than when the alkyl group was methyl.     

The promoter function of molybdenum in Rh/Mo/SiO2 catalysts for CO hydrogenation

A series of Rh/Mo/SiO₂ catalysts with fixed Rh and different Mo contents were studied by FT-IR, chemisorption and CO hydrogenation. The FT-IR results at room temperature under CO atmosphere indicate that the addition of Mo to Rh/SiO₂ suppresses the linear and bridged CO species and promotes the twin CO species, which is consistent with the chemisorption results. It is suggested that the Mo promoter works via stabilization of Rh^1– ions and the coverage of Rh sites. The molybdenum promotes the formation of oxygenates and shifts the selectivity from hydrocarbons to oxygenates.     

Platinum-group metal cyclodextrin complexes and their use as command-cure catalysts in silicones

The Command-Cure concept is defined for a curable formulation as one with long work-like at ambient temperature and rapid cure time at elevated temperature. This concept is explored for a curable silicone system, cured via hydrosilylation. CODMCl₂ complexes (COD=1.5-cyclo-octadiene:M=Pt. Pd) are reacted with beta-cyclodextrin (-CD) to make 11 inclusion compounds,M=Pd.2;M=Pt.4. Compounds2 and4 were analyzed by¹H NMR and X-ray powder diffraction. Their catalytic ability was evaluated in a model system as well as a polymeric system that gels upon cure. Surprisingly, the Pd analog2 was a good command-cure catalyst whereas the guest compound CODPdCl₂,1, was not active in the hydrosilylation reaction. The Pt analog,4, was an effective command-cure catalyst while the corresponding guest. CODPtCl₂,3, was too active at low temperature in the hydrosilylation reaction. Additional Pt compounds and one Rh inclusion compound were evaluated as command cure catalysts. These inclusion compounds were: 11 -CD:[CODRhCl]₂,5: 11 -CD:CpPtMe₃,6 (Cp=cyclopentadienyl): 12 -CD:MeCpPtMe₃,7; 12 -CO:CODPtMe₂,8. The effectiveness of4 8 was evaluated in a number of silicone systems.     

Synthesis and characterization of dinuclear silver(I) complexes with exchangeable nitrile ligands

We have prepared three silver(I) complexes of the type [Ag₂(P ∩ N)₃(NCR)](BF₄)₂ with (R = Me, Et, Ph). The crystal structures of the complexes were determined. The nitrile ligands can be easily exchanged by re-crystallisation in the respective nitrile. The luminescence properties were also investigated.     

Preparation of supported Pt(0) nanoparticles as efficient recyclable catalysts for hydrogenation of alkenes and ketones

A magnetically recoverable Pt(0) catalyst was prepared by in situ H₂ reduction of Pt²⁺ species bound to an amino modified silica-coated magnetic nanoparticles. Compared to ordinary silica (maximum uptake Pt 0.03 wt%), the amino-functionalized silica surfaces were loaded with 1.95 wt% of metal. The supported Pt(0) nanoparticles exhibit high catalytic activity in the hydrogenation of alkenes and ketones under solventless mild reaction conditions. Partially hydrogenated products could also be isolated. The magnetic property of the catalyst grants a fast and efficient product isolation compared to traditional methods used in heterogeneous systems that generally make use of time- and solvent-consuming procedures.     

Preparation of mono(dimethylglyoxime)(triphenylphosphine)-halogenocobalt(I) complexes and their application as homogeneous catalysts in reduction of aromatic nitrocompounds

The complexes [Co(I)(DMGH)(PPh₃)X].C₂H₅OH (X? Cl/Br) have been prepared and characterised by elemental analysis, infrared and electronic spectral studies and magnetic measurements. These compounds have been used as homogeneous catalysts for the reduction of nitrobenzene at atmospheric and higher pressures. From a study of various operational parameters, it has been observed that the reduction at atmospheric pressure was only possible in a basic ethanolic medium and resulted in 64% of azobenzene on input nitrobenzene basis whereas at higher pressure (4.2 × 10³ kN/m²), 60% of aniline on the same basis could be obtained in neutral ethanolic medium. The optimum conditions were established both under normal pressure and under high pressure.     

Preparation of supported Pt(0) nanoparticles as efficient recyclable catalysts for hydrogenation of alkenes and ketones

A magnetically recoverable Pt(0) catalyst was prepared by in situ H₂ reduction of Pt²⁺ species bound to an amino modified silica-coated magnetic nanoparticles. Compared to ordinary silica (maximum uptake Pt 0.03 wt%), the amino-functionalized silica surfaces were loaded with 1.95 wt% of metal. The supported Pt(0) nanoparticles exhibit high catalytic activity in the hydrogenation of alkenes and ketones under solventless mild reaction conditions. Partially hydrogenated products could also be isolated. The magnetic property of the catalyst grants a fast and efficient product isolation compared to traditional methods used in heterogeneous systems that generally make use of time- and solvent-consuming procedures.