Preparation of a new cobalt-containing diphosphine ligand and its reaction towards dicobalt octacarbonyl; X-ray crystal structure of [Co2(CO)4(μ-CO)2{μ-P,P-(μ-PPh2CCPPh2)Co2(CO)6}]

Consecutive reactions of bis(diphenylphosphino)acetylene with Co₂(CO)₈ resulted in an alkyne-bridged, diphosphine-chelated tetracobalt complex, [Co₂(CO)₄(μ-CO)₂{μ-P,P-(μ-PPh₂CCPPh₂)Co₂(CO)₆}] (2), which has been characterized by spectroscopic means as well as X-ray studies.     

Preparation of some supported metallic catalysts from metallic cluster carbonyls

An examination was made of the adsorption of some metallic cluster carbonyls (MCCs), Co₂Rh₂(CO)₁₂, Co₃Rh(CO)₁₂, Co₄(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, and Ru₃(CO)₁₂, from nonaqueous solution onto two typical catalyst supports, γ-alumina and Aerosil silica. With two MCCs, Co₂Rh₂(CO)₁₂ and Ir₄(CO)₁₂, dispersed metallic catalysts were generated, and a study was made of how the main experimental conditions affected the metallic dispersion. MCC adsorption was more facile on γ-alumina than on silica and was often assisted by the presence of oxygen. An ir study showed that initial adsorption of Co₂Rh₂(CO)₁₂ on γ-alumina occurred with the loss of bridging carbonyls, the remaining carbonyls being progressively lost at temperatures >300 K, while adsorption of Ir₄(CO)₂ on γ-alumina resulted in progressive carbonyl loss at 320–620 K. Strong adsorption involves carbonyl loss, probably by ligand exchange with a surface anion, and the effect of oxygen is probably oxidative decarbonylation. Catalysts prepared from Co₂Rh₂(CO)₁₂ or Ir₄(CO)₁₂ were relatively highly dispersed (D ≈ 0.4-1 depending on conditions), and Co₂Rh₂(CO)₁₂ gave a much higher dispersion than was obtained by conventional impregnation using aqueous salt solutions. MCC adsorption in the presence of oxygen favored higher dispersions.     

A highly active bimetallic supported Rh–Co hydroformylation catalyst prepared from RhCl3 and Co2(CO)8

The preparation of a highly active bimetallic SiO₂‐supported Rh–Co catalyst from RhCl₃ and Co₂(CO)₈ (Rh:Co= 1 : 3 atomic ratio) has been studied by IR spectroscopy and ethylene hydroformylation, etc. Two steps are involved in the preparative process: (1) surface‐mediated synthesis of Rh⁺(CO)₂/SiO₂ from calcined RhCl₃/SiO₂; (2) impregnation of Rh⁺(CO)₂/SiO₂ with a Co₂(CO)₈ solution followed by H₂ reduction at 623 K. The IR results of reductive carbonylation of calcined RhCl₃/SiO₂ have been compared to those of uncalcined RhCl₃/SiO₂ at 373 K. In situ IR observations, extraction results and elemental analysis suggest that approximately 50% of RhCl₃ are transformed to Rh₂O₃ on the SiO₂ surface and that calcined RhCl₃/SiO₂ is converted to a mixture of [Rh(CO)₂Cl]₂ and [Rh(CO)₂O₂ (O_s: surface oxygen) under CO at 373 K. When this SiO₂‐supported mixture was submitted to impregnation with a Co₂(CO)₈ solution at room temperature, IR study and elemental analysis show that [Rh(CO)₂Cl]₂ reacts easily with Co₂(CO)₈ on the surface to give RhCo₃(CO)₁₂, whereas [Rh(CO)₂O₂ does not react with Co₂(CO)₈. Catalytic study in steady‐state ethylene hydroformylation shows that a catalyst thus derived is more active than a catalyst derived from RhCo₃(CO)₁₂/SiO₂ and a catalyst derived by coimpregnation of [Rh(CO)₂Cl]₂ and Co₂(CO)₈ on SiO₂. This result suggests that the high rhodium dispersion of [Rh(CO)₂O₂ plays a crucial role in the formation of highly dispersed bimetallic Rh–Co sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and characterization of an unusual tetracobalt-complex; X-ray crystal structure of [Co2(CO)5{μ-P,P(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}]

The reaction of bis(diphenylphosphino)acetylene(DPPA) with Co₂(CO)₈ in toluene at 80 °C for 24 h resulted in an alkyne-bridged, diphosphine-chelated tetracobalt-complex, [Co₂(CO)₅{μ-P,P-(μ-PPh₂CCPPh₂)}][Co₂(CO)₄{μ-P-(μ-PPh₂CCPPh₂)}] 3. The X-ray structural studies of 3 reveals that it can be regarded as a dimerized form of two DPPA bridged dicobalt complex, [Co₂(CO)₆(μ-PPh₂CCPPh₂)] 1.     

Preparation and characterization of Co/SiO2, Co-Mg/SiO2 and Mg-Co/SiO2 catalysts and their activity in CO hydrogenation

Co/SiO₂, Mg-Co/SiO₂ and Co-Mg/SiO2 catalysts were prepared from acetate, nitrate or carbonyl precursors. The catalysts were characterized by XRD, XPS, SIMS and TGA. The steady-state activity and product distribution of the catalysts were evaluated in synthesis gas reactions at 0.5 MPa and 235-290°C using 3 : 1 : 3 molar ratio of Ar : CO : H₂. The activity in CO hydrogenation decreased in the precursor order Co₂(CO)₈>Co(NO₃)₂> Co(CH₃COO)₂, and the probability of chain growth decreased in the precursor order Co(NO₃)₂>Co₂(CO)₈>Co(CH₃COO)₂. Alcohol yields were highest with Co₂(CO)₈, and lowest with Co(NO₃)₂, Magnesium promotion influenced the catalyst activity and decreased the CO₂ formation, but the promotion effects were less profound than those of the precursor. Surface studies on partially magnesium covered cobalt foil model catalysts suggested that magnesium promotes CO dissociation and chain growth, neither of which were, however, observed in the supported catalysts.     

SiO2‐supported bimetallic Rh–Co catalysts derived from [Rh(CO)2Cl]2 and cobalt carbonyls

According to the results of IR characterization and catalytic study in ethylene hydroformylation, bimetallic Rh–Co catalysts can be efficiently prepared from [Rh(CO)₂Cl]₂ and cobalt carbonyls by co‐impregnation on SiO₂. The reaction of Co₂(CO)₈ with [Rh(CO)₂Cl]₂ (Rh : Co = 1 : 3 atomic ratio) gives rapidly RhCo₃(CO)₁₂ on the surface of SiO₂. Although Co₄(CO)₁₂ is not reactive with [Rh(CO)₂Cl]₂ on SiO₂ to form directly RhCo₃(CO)₁₂, an equivalent bimetallic catalyst can be easily obtained from ([Rh(CO)₂Cl]₂ + Co₄(CO)₁₂)/SiO₂ or its derivative (Rh⁺ + Co²⁺)/SiO₂ (Rh : Co = 1 : 3 atomic ratio) under reducing conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Y-Faujasite Encapsulated Co Clusters: Synthesis, Characterization and Theoretical Model as Probe of the Methane Homologation

The adsorption of Co₂(CO)₈ onto the dehydrated Y-faujasite powder under an N₂ atmosphere and onto the tetrahydrofuran slurry of Y-faujasite under a mixed CO and H₂ atmosphere predominately yielded supported Co₄(CO)₁₂ and supported Co₆(CO)₁₆, respectively. The molecular cobalt-carbonyl clusters and their decarbonylated products have been structurally characterized by extended X-ray absorption fine structure (EXAFS). The decarbonylated sample a possesses a cluster of two Co atoms and the decarbonylated sample b has a cluster phase of three Co atoms. The decarbonylated sample a exhibited higher CH₄ conversion and C₂₊ selectivity (C₂₊ selectivity = ∑nC _n(n = 2–5)/∑nC _n (n = 1–5) * 100%) in comparison with the decarbonylated sample b in methane homologation. A density functional theory (DFT) model was employed to calculate Co clusters adsorbed on a silica substrate which simulates Y-faujasite encapsulated Co clusters. The structural geometries, net spin electronic charge densities, energies of the metal–silica and metal–metal interactions in stable geometries are discussed and used to interpret the cluster size dependence of the catalytic activity and selectivity to C ₂₊ hydrocarbons in the methane homologation.     

Umsatz- und Selektivitätsverhalten von Dicobaltoctacarbonyl und Cyclopentadienylcobaltdicarbonyl auf Silicagel-, Alumosilicagel- und Aluminiumoxid-Trägern bei der Hydroformylierung von Hex-1-en

Conversion and Selectivity in Hydroformylation of Hex-1-en with Silica-Gel-, Silica-Alumina-Gel and Alumina-Oxide- Supported Dicobalt Octacarbonyl and Cyclopentadienylcobalt Dicarbonyl The catalytic influence of silica-gel-, silica-alumina-gel- and alumina-oxide-supported Co₂(CO)₈ and CpCo(CO)₂ on the conversion and selectivity in hydroformylation of hex-1-en has been studied at 353 K under 120 bar syngas pressure in acetonitrile. The support systems were prepared by impregnation of SiO₂ (Grace), SiO₂/4% Al₂O₃ (Kali Chemie), SiO₂/11% Al₂O₃ (Kali Chemie) and Al₂O₃ (Kali Chemie) using Co₂(CO)₈ and CpCo(CO)₂ solutions in pentane, dichlormethane and 2-chlorpropane. The results are discussed with regard to some measured relevant support characteristics. The turn over numbers especially those of silica-gel- and silica-alumina-gel supported Co₂(CO)₈ and CpCo(CO)₂ show positive effects in relation to a heterogeneous catalytic process within these reactions.     

Preparation and properties of poly(ethylene glycol)-block-poly(acrylic acid)-coated cobalt nanocrystals

Reported in this paper are the preparation and properties of ?-Co nanocrystals coated by poly(ethylene glycol)-block-poly(acrylic acid) (PEG-b-PAA). These particles were prepared via the thermal decomposition of Co₂(CO)₈ at 185 °C in 1,2-dichlorobenzene, in the presence of the surfactant PEG-b-PAA and the co-surfactant trioctylphosphine oxide. At a given initial Co₂(CO)₈ concentration, the size of the particles increased with increasing Co₂(CO)₈-to-PEG-b-PAA molar ratio, and could be tuned between ∼5 and ∼20 nm. The size distribution of the particles narrowed as the Co₂(CO)₈ concentrations increased. The resultant particles were dispersible in a wide range of solvents, including chloroform, N,N-dimethylforamide, and water, which solubilized PEG. Magnetic measurements revealed that the particles possessed saturation magnetization close to that of bulk Co, suggesting high purity of the particles.     

Use of catalytic reactions to probe Mg-Al mixed oxide surfaces

The atmospheric hydroformylations of ethylene and propylene were investigated over SiO₂-supported Rh₄(CO)₁₂, Co₂(CO)₈, Rh₂Co₂(CO)₁₂ and RhCo₃(CO)₁₂-derived catalysts. The bimetal cluster-derived catalysts showed excellent activities for the formation of oxygenates. In situ IR study on partially dehydroxylated SiO₂-supported RhCo₃(CO)₁₂ suggested that the bimetal cluster framework may be preserved after decarbonylation under H₂ at 623 K and may be recarbonylated at room temperature. A strong physisorption of RhCo₃ (CO)₁₂ on SiO₂ is proposed, due to a nucleophilic attack of surface oxygen on the Co atoms, which promotes a metal-support interaction and thus stabilizes the bimetal cluster framework. A subcarbonyl bimetal cluster is thought to be the actual catalytic species on the surface.     

CO hydrogenation towards higher alcohols catalysed on SiO2-grafted and zeolite-entrapped Ru,Co and RuCo bimetallic clusters: Their EXAFS and FTIR characterization and catalytic performances

Some Ru and Co carbonyl clusters in zeolite pores such as Ru₃(CO)₁₂/NaY, [HRu₆(CO)₁₈]^–/NaY, [Ru₆(CO)₁₈]^2–/NaX, Co₄(CO)₁₂/NaY and Co₆(CO)₁₆/NaY were prepared by the ship-in-bottle technique, and characterized by FTIR and EXAFS. The RuCo bimetallic carbonyl cluster was prepared by reductive carbonylation of the oxidized RuCo/NaY, which provides the proposed assignment to [HRUCo₃(CO)₁₂]/NaY. The tailored Ru, RuCo and Co catalysts were prepared by H₂ reduction from the precursors, e.g. Ru, RuCo bimetallic and Co carbonyl clusters impregnated on SiO₂ and entrapped in NaY and NaX zeolites. The RuCo bimetallic carbonyl cluster-derived catalysts showed substantially higher activities and selectivities for oxygenates such as C₁–C₅ alcohols in CO hydrogenation (CO/H₂ = 0.33-1.0, 5 bar, 519–543 K). By contrast, hydrocarbons such as methane were preferentially obtained on the catalysts prepared from Ru₆, Ru₃ and Co₄ carbonyl clusters and provided lower CO conversion and poor selectivities for oxygenates. The RuCo bimetals are proposed to be associated with the selective formation of higher alcohols in CO hydrogenation.     

Characterization and magnetic properties of carbon-coated cobalt nanocapsules synthesized by the chemical vapor-condensation process

Carbon-coated cobalt nanocapsules were synthesized by the chemical vapor-condensation process with cobalt carbonyl (Co₂(CO)₈) used as precursor and carbon monoxide (CO) as carrier gas. The characterization and magnetic properties of carbon-coated cobalt nanocapsules were investigated systematically. The transmission electron microscope (TEM) images showed that the as-prepared nanoparticles consist of a metal core and an amorphous carbon shell. X-ray diffraction and TEM selected area diffraction revealed the presence of f.c.c. Co phase, h.c.p. Co phase, and minority Co₂C, Co₃C phases. The saturation magnetization at room temperature of the nanocapsules is 146.9 Am² kg⁻¹, which is 90% of the bulk ferromagnetic element counterpart. The coercive force at room temperature of the nanocapsules is 0.12 T, while the ratio of remnant to saturation magnetization M_r/M_s is about 0.4. The saturation magnetization and the coercive force increase with increasing the decomposition temperature, mainly due to the increase of the size of the magnetic particles. The decomposition of the cobalt carbonyl (Co₂(CO)₈) and CO gas can decrease efficiently the oxygen content in nanocapsules. The metallic Co nanoparticles completely coated by carbon can resist the dilute acid erosion as well as the oxidation. The thermal stability of the Co nanocapsules is also studied.     

Low-temperature CO oxidation by Co3O4 nanocubes on the surface of Co(OH)2 nanosheets

CO oxidation has been performed on Co₃O₄ nanocubes and Co(OH)₂ nanosheets as model catalysts. The reaction rate of CO on Co₃O₄/Co(OH)₂ nanocomposites obtained by one-pot synthesis is about ~ two orders of magnitude higher than that on Co₃O₄ nanomaterials. The catalytic behaviors of different nanomaterials revealed that the assembly with nano building blocks cause the catalytic sites much more active for CO oxidation. The kinetic data showed that the activation energy for CO oxidation over Co₃O₄/Co(OH)₂ nanocomposites was lower than that of other nanomaterials. Since Co(OH)₂ nanosheets can prevent Co₃O₄ nanocubes aggregating, nanocomposites kept good catalytic stability.     

Metal-organic framework as a host for synthesis of nanoscale Co3O4 as an active catalyst for CO oxidation

Co₃O₄ nanoparticles were prepared from cobalt nitrate that was accommodated in the pores of a metal-organic framework (MOF) ZIF-8 (Zn(MeIM)₂, MeIM = 2-methylimidazole) by using a simple liquid-phase method. The ZIF-8 host was removed by pyrolysis under air and subsequently washing with an NH₄Cl–NH₃·H₂O aqueous solution. Transmission electron microscopy (TEM) analysis shows that the obtained Co₃O₄ is composed of separate nanoparticles with a mean size of 18 nm. The Co₃O₄ nanoparticles exhibit excellent catalytic activity, cycling stability, and long-term stability in the low temperature CO oxidation.     

Selective synthesis of alcohols from syngas and hydroformylation of ethylene over supported cluster-derived cobalt catalysts

Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co₂(CO)₈ with ZnO, MgO and La₂O₃ supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La₂O₃ > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C₁-C₃) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co²⁺/[Co(CO)₄]^– ion-pairing species.     

Cobalt Carbonyl‐Based Catalyst for Hydrosilylation of Carboxamides

The cobalt carbonyl [Co₂(CO)₈] complex is employed as a useful catalyst for the reduction of tertiary amides to the corresponding tertiary amines using 1,1,3,3‐tetramethyldisiloxane (TMDS) and poly(methylhydrosiloxane) (PMHS) as silane reagents under thermal (100 °C) or photo‐assisted conditions (UV, 350 nm at room temperature). Of particular interest, a low catalytic amount (0.5 mol%) of [Co₂(CO)₈] is used to perform the reaction with 2.2 equiv. of PMHS at 100 °C for 3 h. This reaction is the first example of a cobalt‐catalyzed hydrosilylation of amides.

     

Cooperative effect between iridium and platinum in the carbonylation of methanol to acetic acid

The iodocarbonyl monomer [PtI₂(CO)₂] 7 promotes the iridium catalyzed carbonylation of methanol to acetic acid at low water contents. Studies based on low pressure or high pressure NMR and the use of labeled reactants were conducted close to the real conditions of catalysis in order to get a deeper insight into this system. Carbonylation of CH₃I at low water contents proceeds slowly and the migratory CO insertion step, leading from H[IrI₃(CH₃)(CO)₂] 2-H to H[IrI₃(COCH₃)(CO)₂] 6-H is rate limiting. The dimer [PtI₂(CO)]₂ 7′ reacts immediately with [PPN][IrI₃(CH₃)(CO)₂] 2-PPN (PPN is Ph₃P=N⁺=PPh₃) under nitrogen to afford a mixture of species, among which the key heterobinuclear [Ir–Pt] intermediate [PPN][IrI₂(CH₃)(CO)₂(μ-I)PtI₂(CO)] 8-PPN has been identified; [PPN][IrI₂(CH₃)(CO)₂(μ-I)PtI₂(CO)] 8-PPN can in its turn lead to the formation of [PPN][PtI₃(CO)] 9-PPN, [IrI₂(CH₃)(CO)₂(solv)] 10, [Ir₂I₂(CH₃)₂(μ-I)₂(CO)₄] 3′ and [PPN][Ir₂I₄(CH₃)₂(μ-I)(CO)₄] 11-PPN; all of these species have been characterized. Under CO pressure, [PPN][IrI₂(CH₃)(CO)₂(μ-I)PtI₂(CO)] 8-PPN is a short-lived species that quickly leads to [IrI₂(CH₃)(CO)₃] 4 and [PPN][PtI₃(CO)] 9-PPN showing that the main role of the platinum promoter is to abstract an I⁻ ligand from [PPN][IrI₃(CH₃)(CO)₂] 2-PPN. Under catalytic conditions, I⁻ is abstracted from H[IrI₃(CH₃)(CO)₂] by [PtI₂(CO)₂] 7 and the rate determining step is accelerated; the relevant species H[IrI₃(CH₃)(CO)₂] 2-H, H[IrI₃(COCH₃) (CO)₂] 6-H and H[PtI₃(CO)] 9-H have been observed under 30 bar of CO. A catalytic cycle is proposed, which depicts the cooperative effect between the iridium catalyst and the platinum promoter.     

Novel binary chlorides containing TiCl3 as components of coordination catalysts for ethylene polymerization. I. Synthesis and characterization of the solid solutions obtained

New binary chlorides have been obtained by reacting TiCl₄ with V(CO)₆, Cr(CO)₆, Mn₂(CO)₁₀, Mn(CO)₅Cl, Ni(CO)₄, Co₂(CO)₈, Fe(CO)₅, or Mo(CO)₆. The reactions yield quantitatively mixed chlorides having the general formula MCl_n·n TiCl₃, where n = 2 or 3 and M is a divalent or trivalent transition metal cation. MCl_n is generally isomorphous with the α- or γ-modification of TiCl₃. X-Ray and spectroscopic investigations indicate that the mixed chlorides obtained are solid solutions. High surface area values are associated with the adducts displaying lower crystallinity. Catalyst efficiencies two or three times higher than that of AlCl₃·3TiCl₃ were observed in the low-pressure polymerization of ethylene (HDPE) when some binary chloride was associated with Al(i-C₄H₉)₃. These results allow treating the obtained solid solutions as reference systems of high-yield catalysts for HDPE synthesis.     

Metallostars and metallodendrimers based upon hexaphenylbenzene cores

Stars and dendrimers based on a hexaphenylbenzene core and containing 12 or 30 alkyne functionalities have been prepared; reactions with Co₂(CO)₈ lead to cobaltadendrimers containing 24 or 60 Co atoms.     

Supported tetranuclear carbonyl clusters: 1. Framework distortion and catalytic activity in hydroformylation

In comparison with the structural data determined by EXAFS, the catalytic activities of supported clusters Co₄(CO)₁₀ (PPh)₂/SiO₂ and PhCH₂(CH₃)₃NFeCO₃(CO)₁₂/polystyrene have been investigated. Consistent increase (or decrease) between Co-Co bond distance and catalytic activity in hydroformylation suggests that the cleavage of the metal-metal bond is the first step towards the formation of the catalyst center and the cluster framework distortion is beneficial to the catalyst in raising the catalytic activity in hydroformylation.Project supported by National Natural Science Foundation, P. R. China.