Addition polymerisation vs. ROMP on cyclic and strained olefins with the Mo(CO)5PPh3/alkylaluminums catalysts

The polymerisation of cyclic and strained monomers such as bicyclo[2.2.1]hept-2-ene (norbornene, NBE) and bicyclo[2.2.1]hepta-2,5-diene (norbornadiene, NBDE) with the catalytic systems Mo(CO)₅PPh₃/alkylaluminums was studied. From the polymers produced we demonstrate the existence of an antagonism between the ROMP (Ring-Opening-Metathesis-Polymerisation) mecanism and the olefin addition polymerisation mecanism. In addition ROMP mecanism is affected by the solvent. These catalysts also promotes the isomerisation of double bonds, as indicated by the ESR signal observed for the conjugated crosslinked polyNBDE produced by ROMP. Received: 5 August 1996/Revised version: 22 October 1996/Accepted: 25 October 1996     

Homogenous catalytic conjugation of polyunsaturated fats by chromium carbonyls

Various arene-Cr (CO)₃ complexes and Cr(CO)₆ are effective soluble catalysts for the conjugation of polyunsaturated fats. Methyl benzoate-Cr(CO)₃ is one of the most active catalysts. The following conjugation levels were obtained: methyl linoleate, 65%; methyl linolenate, 45%; the polyunsaturates in soybean and safflower oils, 73%; and in linseed oil 48%. Conjugated dienes from linoleate were predominantlycis,trans in configuration. Their double bonds were distributed between C₅ and C₁₆ of the fatty acid chain. Hydrogenation and dehydrogenation are side reactions, which seem to limit the yield of conjugated dienes from methyl linoleate. A conjugation mechanism is proposed that involves allyl-HCr(CO)₃ complexes as intermediates undergoing 1,3- and 1,5-hydrogen shifts. Presented at the AOCS Meeting, San Francisco, April 1969. No, Utiliz. Res. Dev. Div., ARS, USDA.     

Synthesis,structure and catalytic activities for hydrogen transfer reaction of the carbonyl ruthenium(II) complex containing polypyridine and phosphine ligands

The synthesis and characterization of new ruthenium(II) carbonyl complexes containing polypyridine and triphenylphosphine ligands is reported. Crystallographic information obtained for the trans-PPh₃-[Ru(biq)(PPh₃)₂(CO)]Cl₂ complex (biq = 2,2’-biquinoline) reveals five-coordination on the metal. The complexes were studied as catalysts in hydrogen transfer reactions in basic solution. Turnover frequencies in the 2250-817 h^-1 range were determined in 1 hour of reaction with a substrate/catalysts ratio of 830.     

The polymerization of propargyl halides (Cl,Br) using M(CO)5PPh3/R x AlCl3-x (M=Mo,W) as catalysts

Summary Propargylchloride (PCl) and propargylbromide (PBr) were polymerized in good yields using M(CO)₅PPh₃/R_xAlCl_3-x as catalysts (M=W, Mo). Mo was found to be more effective than W. The presence of chlorine atoms in co-catalyst was important for the activation of the catalyst. The obtained polymers were coloured, insoluble in all organic solvents and stable until 150°C. From their IR and ESR spectra is concluded that the polymers have highly conjugated structures. The oligomeric products were constituted mainly from cyclotrimers. In the case of Mo-catalyst only 1,2,4-cyclotrimer was obtained; a mixure of 1,2,4 and 1,3,5-derivatives were formed using W-catalysts.     

The characteristics of metallocene/Ziegler-Natta hybrid catalysts supported on the recrystallized MgCl2

A metallocene catalyst or a metallocene/Ziegler-Natta hybrid catalyst supported on MgCl₂ was studied for application to the commercial slurry phase process and to the control of MWD of the polymer produced. The MgCl₂ support was prepared by the recrystallization method with different solvents: alcohols and H₂O. The recrystallized MgCl₂ support was pretreated with triisobutylaluminum (TiBAL) or trimethylaluminum (TMA), methylaluminoxane (MAO), to give different supporting environments. Metallocene/Ziegler-Natta hybrid catalysts on MgCl₂ were prepared by first supporting the metallocene catalyst, followed by the Ziegler-Natta catalyst after pretreatment with an alkylaluminum compound. The type of solvent plays a role in providing a suitable environment in the support for impregnating catalysts. The hybrid catalyst, whose support was recrystallized in n-propanol (n-PrOH) and pretreated with TiBAL, showed the highest molar ratio of Zr/Ti= 1/2.71. But the hybrid catalyst, whose support was recrystallized in H₂O and pretreated with MAO, showed the best hybrid effect showing a variety of bimodal peaks in proportion to the ratio of MAO/TEA in GPC analysis. This effect might be due to steric factor and polarity of solvent, as well as the pretreatment material. It is concluded that the MWD of polyethylene produced by metallocene/Ziegler-Natta hybrid catalyst that is supported on MgCl₂ can be controlled by regulating the amounts of MAO and TEA added as cocatalysts and by the use of different solvents and pretreatment materials.     

Homogeneous catalytic hydrogenation of unsaturated fats: Group VIB metal carbonyl complexes

Carbonyl complexes of Cr, Mo and W have been studied as soluble catalysts for the hydrogenation of methyl sorbate and of methyl esters from soybean oil. With methyl sorbate, relative catalytic activity decreased in the approximate order: mesitylene-Mo(CO)₃, cycloheptatriene-Mo(CO)₃, cycloheptatriene-Cr(CO)₃, bicyclo (2,2,1) hepta-2,5-diene-Mo(CO)₄, chlorobenzene-Cr(CO)₃, methyl benzoate-Cr(CO)₃, mesitylene-W(CO)₃, benzene-Cr(CO)₃, toluene-Cr(CO)₃, mesitylene-Cr(CO)₃, and hexamethylbenzene-Cr(CO)₃. Order of catalytic activity was related to thermal stability of the complexes during hydrogenation. With mesitylene-M(CO)₃ complexes, selectivity varied in the order Cr>Mo>W. Under certain conditions the mesitylene complexes of W, Cr and Mo reduced methyl sorbate respectively to methyl 2-, 3-, and 4-hexenoates as main products. The more active and thermally stable Cr(CO)₃ complexes catalyzed effectively the hydrogenation of linoleate and linolenate in soybean oil esters with little or no stearate formation. The hydrogenated products formed with the benzoate complex at 165–175 C contained 50–67% monoene, 18–30% diene, 2–7% conjugated diene, and only 3–7%trans unsaturation. Linolenate-linoleate selectivity values varied from 3 to 5 and linoleate-oleate selectivity from 7 to 80. Monoene fractions had 40–50% of the double bond in the C-9 position; the rest of the unsaturation was distributed mainly between the C-10 and C-12 positions. Conjugation is apparently an intermediate step in the hydrogenation of linoleate and linolenate. The Cr(CO)₃ complexes are unique in catalyzing the hydrogenation of polyunsaturated fatty esters to monounsaturated fatty esters of lowtrans content. Presented at AOCS-AACC Joint Meeting, Washington, D.C. April, 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Bisphosphino ureas: flexible ligands with rigid backbone

The nickel(0) complex [Ni{η²-(PPh₂NMe)₂CO}{η¹-(PPh₂NMe)₂CO}] 1 was obtained by the reaction of NiCl₂·6H₂O with two equivalents of the ligand (PPh₂NMe)₂CO in the presence of zinc as reducing agent. The structure of 1 was unambiguously determined by ¹H and ³¹P–{¹H} NMR spectroscopy and compared to the known structures of the extremely strained Pd(II) and Mo(0) complexes of (PPh₂NMe)₂CO.     

Gas phase hydroformylation of ethylene using organometalic Rh-complexes as heterogeneous catalysts

The heterogeneously catalysed gas phase hydroformylation of ethylene to propionaldehyde was studied over solid RhCl(PPh₃)₃ and RhCl(CO)(PPh₃)₂. At 3 bar and 185 °C, an active phase formed from RhCl(PPh₃)₃ which was different from RhCl(CO)(PPh₃)₂ under the reaction conditions studied. The selectivity of RhCl(PPh₃)₃ to propanal was much better than that of supported Rh-metal. Thus, solid metal-complexes operated in gas phase reactions clearly hold promise as a new class of heterogeneous catalysts.     

Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh₃)(NO₃) (1) and a phosphine-stabilized gold cluster [Aug(PPh₃)₈](NO₃)₃ (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe₂O₃, TiO₂, and SiO₂ were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h₂/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe₂O₃ and TiO₂ were much more efficient supports than SiO₂ for the gold particles which were characterized by XRD and EXAFS.     

Half-sandwich ruthenium complexes for the controlled radical polymerisation of vinyl monomers

Ruthenium complexes of the type [RuX(Cp^#)(PPh₃)₂] (X=Cl and H; Cp^#=Cp, Cp*, indenyl, and carboranyl) catalyse the radical polymerisation of styrene and n-butyl acrylate, and both the catalyst activity and the degree of control of the polymerisation strongly depend on the Cp^# ligand and the monomer.     

Isospecific polymerization of styrene with supported nickel acetylacetonate/methylaluminoxane catalysts

Summary The polymerization of styrene with catalysts based on Ni(acac)₂ supported on SiO₂ and Al₂O₃ was investigated. Using catalysts based on MAO supported on silica, a highly isotactic polystyrene was obtained. Nevertheless, the Al₂O₃-supported catalyst can promote isospecific polymerization activated by common. alkyl aluminum compounds even by any prior support treatment with MAO. Received: 3 March 1998/Revised version: 14 April 1998/Accepted: 14 April 1998     

Effect of the preparation method on the surface coverage of Mo/Al2O3 catalysts

Two series of Mo/Al₂O₃ catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO₂ chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO₂ and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO₂ chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.     

Diastereotopic relationship between planar and central chiralities in the formation of Ru(η3-allyl)(CO)(PPh3)(L–L′) complexes

Hydride ruthenium complexes, RuHCl(CO)(PPh₃)₂(L–L^′) 3 (L–L^′=bidentate ligand having nitrogen and oxygen) react with allenes to give Ru(η³-allyl)(CO)(PPh₃)(L–L^′) complexes 5 in good yields via hydrometalation reaction. The complexes 5 have planar chirality at the η³-allyl ligand and central chirality at the Ru metal, and consist of one pair of enantiomers. Ligand substitution reaction of Ru(η³-allyl)Cl(CO)(PPh₃)₂ complexes 6 with bidentate ligands (L–L^′) also afford the complexes 5 which have the same stereochemistry as those formed by the hydrometalation reaction. The planar chirality is controlled by the central chirality at the Ru metal in both the formations of the complexes 5. The structure of 5a (L–L^′=N–N bidentate ligand) was determined by the X-ray crystal structure analysis.     

Alkene and Alkyne Insertion into Hydrogen-Transition Metal Bonds Catalyzed by Palladium(0) Complex

Smooth, reversible and Markovnikov selective alkene insertion of ethyl acrylate, acrylonitrile, and ethylene to MHCp(CO)₃ (M = Mo, W) or MnH(CO)₅ has been catalyzed by Pd(PPh₃)₄ at 20 °C. Cis-selective insertion of acetylene and dimethyl acetylenedicarboxylate into MHCp(CO)₃ (M = Mo, W) also proceeded smoothly.     

Catalyzed polymerization of cycloolefins

The catalyzed polymerization of cycloolefins may lead to a ring retention polymer product or to a polyalkenamer. The homogeneous catalysts, derived from V, W, Mo, and Re transition metal complexes, normally require the synergistic use of an alkylaluminum cocatalyst. Trans-1, 5-poly-alkenamers exhibit elastomeric properties and might be suitable for tire manufacture.     

Polymerization of ethylene and ethylene/1-hexene over Ziegler–Natta/metallocene hybrid catalysts supported on MgCl2 prepared by a recrystallization method

MgCl₂ for use as a catalyst support was prepared by dissolution in methanol and recrystallization in n-decane, followed by vacuum-drying at 2,000 rpm. The prepared support was modified by treatment with alkylaluminum compounds. The activity profile of ethylene over the supported catalysts persisted for periods up to 1 h during the polymerization. The prepared Ziegler–Natta/metallocene hybrid catalysts exhibited the characteristics of both metallocene and Ziegler–Natta catalysts. The polymer produced by the hybrid catalysts gave bimodal peaks in differential scanning calorimetry analysis for ethylene and ethylene/1-hexene polymerization, suggesting that the polymer was composed of two different lamellar structures that were polymerized by each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1707–1715, 1998     

Hydrogenation of nitriles with iridium-triphenylphosphine complexes

Reactions of cationic iridium(I)-COD (COD = 1,5-cyclooctadiene) complexes, [Ir(COD)(PhCN)(PPh₃)]ClO₄ (1), [Ir(COD)(PPh₃)₂]ClO₄ (2) and [Ir(COD)(PhCN)₂]ClO₄ (3) with nitriles under H₂ catalytically produce primary, secondary and tertiary amines. Hydrogenation of nitriles (RCN) gives HCl salts of amines (RCH₂NH₂HCl, (RCH₂)₂NH HCl) in CH₂Cl₂. Secondary and tertiary amines seem to be produced by the reactions of RCN with primary and secondary amines, respectively under H₂ in the presence of catalysts. The hydrogenation in the presence of1 and2 is homogeneously catalyzed by soluble iridium-PPh₃ complexes formed in the reactions of1 and2 with H₂ and RCN whereas the hydrogenation in the presence of3 is heterogeneous by metallic iridium powders produced in the reduction of3 by H₂.     

Preparation of Co–Mo/B2O3/Al2O3 catalysts for hydrodesulfurization: Effect of citric acid addition

The effect of citric acid (CA) addition was studied on the HDS of thiophene over Co–Mo/(B)/Al₂O₃ catalysts. The catalysts were characterized by means of LRS, Mo K-edge EXAFS, NO adsorption capacity measurements, and UV–vis spectra. The catalysts were subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co in order to get deeper insights into the effect of citric acid addition. It was shown that the HDS activity was enhanced by the citric acid addition up to the CA/Mo mole ratio of around 1 and leveled off with further addition. The amount of Co anchored by the CVD was increased by the addition of citric acid, suggesting an increase in the dispersion of MoS₂ particles on the catalyst by the simultaneous presence of Co, Mo and citric acid, in conformity with the increase in the NO adsorption capacity. In contrast to Co–Mo catalysts, the edge dispersion of MoS₂ particles in Mo/B/Al₂O₃ was not affected by the addition of citric acid. The LRS, UV–vis spectra and Mo K-edge EXAFS showed that Co–CA and Mo–CA surface complexes are formed by the addition of citric acid. The Co–CA surface complex is more preferentially formed on CoMo/Al than on CoMo/B/Al, in agreement with a greater promoting effect of citric acid at a lower CA/Mo mole ratio for CoMo/Al than for CoMo/B/Al.     

Hydrogenation of ethylene carbonate catalyzed by lutidine-bridged N-heterocyclic carbene ligands and ruthenium precursors

A series of air and moisture-stable lutidine-bridged N-heterocyclic carbene (NHC) ligands and commercial Ru precursors were applied as catalysts for hydrogenation of ethylene carbonate to glycol and methanol. N-Butyl-substituted CNC-pincer ligand L1 and RuHCl(CO)(PPh₃)₃ catalytic system exhibited the highest catalytic activity with 99% conversion of ethylene carbonate, 92% glycol and 42% methanol yields. The high catalytic activity was attributed to the in-situ formation of Ru-NHC complexes in the presence of base. This facile, stable and efficient catalytic system provided a new method for the indirect conversion of CO₂.     

Interactions of rhodium carbonyl compounds supported on inorganic oxides with CO,H2 and propylene

RhCl(CO)(PPh₃)₂, RhH(CO)(PPh₃)₃, and [RhClfCO)₂]₂ were supported on silica gel, γ-alumina, titania.and magensia in 3 to 5 wt % to study the interactions of rhodium carbonyl with the surface of inorganic oxides When trans-RhCI(CO)(PPh₃)₂ was supported on the surface of silica gel, cis-RhCl(CO) (PPh₃)₂ species was detected via the splitting of the CO infra red stretching band of trans-RhCI (CO)(PPh₃)₂. With other supports, same phenomenon was observed but with the different pattern of intensities of the splitted CO stretching bands. RhH(CO)(PPh₃)₃ was easily decarbonylated, after interacting with the surface of silica gel, γ-alumina, and titania. However, [RhCl(CO)₂]₂ was decarbonylated on the surface of inorganic oxides mentioned above and most of supported [RhCl(CO)₂]₂ converted to a stable surface carbonyl species [M-OH-RhCI(CO)₂; M = Si, Al, Ti]. Diffuse reflectance infrared spectroscopy (DRS) was used to study the interactions of 5 wt % RhCl(CO)(PPh₃)₂ supported on silica gel with H₂, CO and/or propylene at various temperatures. The result indicated that the surface intermediates formed from the interaction of RhCl(CO)(PPh₃)₂ with CO, H₂ and C₃H₆ were not identical to the corresponding liquid-phase intermediates of RhCl(CO)(PPh₃)₂ in the presence of solvent.