Supported metals and metal oxides as promoters for the metal dimer and cluster catalysed co substitution reaction

Promotional effects due to PtO₂, PdO, Pd/C and Pd/CaCO₃ on the metal dimer or cluster (e.g. [(η⁵-C₅H₅)Fe(CO)₂]₂, Ru₃(CO)₁₂, Ir₄(CO)₁₂) catalysed reaction between metal carbonyls and isonitriles are shown to lead to enhanced reaction rates for the metal carbonyl substitution reaction.     

Mixed oxides of transition metals as catalysts for total ethanol oxidation

Oxides of transition metals could be suitable alternatives to catalysts based on noble metals in the oxidation processes used for the abatement of volatile organic compounds. Mixed oxides of transition metals can exhibit good efficiency and thermal stability, as well as being inexpensive. In this work, oxide catalysts containing various combinations of Cu, Co, Ni, Mn, and Al, grained or supported on oxidised aluminium foil Al₂O₃/Al, were studied in terms of their chemical and physical properties, including their chemical composition, porous structure, phase composition, reducibility, and activity in total ethanol oxidation. Ternary co-precipitated catalysts in the form of grains obtained from layered double hydroxide-like precursors were highly active, especially those containing manganese. Deposition of the selected precursors on an anodised aluminium foil-support afforded less active catalysts, mainly because the required metal molar ratios were not achieved, and insufficient amounts of metals were deposited. However, by controlling the preparation conditions (pH), higher loading of active components and higher catalytic activity were obtained.     

Thermal degradation of the transition metal carbonyl complexes

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅(dppm) (whereM=Cr, Mo and W;dppm=Bis-(diphenylphosphino)-methane) has been studied using TG and DSC technics and their results reported. All the complexes facilely lose a carbonyl ligand (CO) below 200 °C. The kinetic analysis on the molybdenum complex suggested a first order dissociation pathway for this decarbonylation process. Dephosphination occurred at high temperature, followed by further decarbonylations. The enthalpy changes associated with the first decarbonylation are reported. The measured kinetic parameters are in good agreement with the literature values on similar systems obtained from solution studies.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonyl-Komplexen des Typs M(CO)₅(dppm) (M=Cr, Mo oder W; dppm=Bis-(diphenylphosphino)-methan) wurden mittels TG und DSC untersucht. Alle diese Komplexe geben unterhalb 200 °C leicht einen Carbonylliganden (CO) ab. Die für den Molybdänkomplex ausgeführte kinetische Analyse deutet auf einen Dissoziationsverlauf erster Ordnung für diesen Decarbonylierungsprozeß hin. Bei hohen Temperaturen erfolgt Dephosphinierung, gefolgt von weiterer Decarbonylierung. Die sich auf den ersten Decarbonylierungsschritt beziehenden Enthalpieänderungen werden angegeben. Die gemessenen kinetischen Parameter stimmen gut mit Literaturwerten ähnlicher Systeme überein.

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M(CO)₅(dppm), M=Cr, W;dppm=-. 200° . . , . , . , .

     

The role of early transition metal azides as catalysts of the ring-opening reaction of epoxides with trimethylsilylazide

Complexes of early transition metals (titanium, vanadium, …) catalyse the reaction of epoxides with Me₃SiN₃. When an azido complex is used as precursor, the reaction follows an overall second-order law and the rate constant is proportional to the complex concentration. The regioselectivity (α- or β-cleavage of the ring) is compared to that of the stoichiometric reaction of the transition metal azide with epoxides. It is concluded that the catalytic mechanism involves the intermediary formation of a complex resulting from the nucleophilic attack of the epoxide ring by the N₃ group bonded to the transition metal atom.     

Basicity of transition metal carbonyl complexes: VIII. An infrared study of the reaction of aluminium chloride with some cyclopentadienyl and arenecarbonyl transition metal complexes

The interaction of cyclopentadienyl and arene derivatives of carbonyl complexes of Group V, VI and VII transition metals with AlCl₃ in benzene and CH₂Cl₂ solutions has been studied by IR spectroscopy.The formation of adducts involving the metal atom or the carbonyl oxygen atom was observed. The reaction path depends on the structure of the complex and on the nature of the solvent. In benzene the adduct formation at the CO ligand is more favourable than in CH₂Cl₂ solution. Introduction of a phosphine ligand in the place of the CO group or introduction of donor substituents into the π-ring increases the basicity of the central metal atom and makes adduct formation at the metal more probable.The basicity of the metal atom in complexes with the same ligands increases with increases of atomic number in the group. CpRe(CO)₂Br₂ forms adducts with AlCl₃ at the bromine atoms ($\text{1}\text{1}$ and $\text{sol1}\text{2}$). For Fe(CO)₄PPh₃ and Fe(CO)₃(PPh₃)₂ complex formation takes place at the iron atom.     

Palladium N-methylimidazolium supported complexes as efficient catalysts for the Heck reaction

Different N-methylimidazolium supported ligands have been easily synthesized. The palladium complexes derived from those materials can be used for the catalysis of the Heck reaction giving excellent yields, selectivities and very good TON and TOF values. The supported Pd-pincer complexes show an increased stability, and provide a clear improvement in the recovery and reuse for the supported catalysts.     

Thermal degradation of transition metal carbonyl complexes. Part II

The thermal degradation of three monosubstituted hexacarbonyl complexes, M(CO)₅py (where M=Cr, Mo, and W; py=pyridine) has been studied by thermogravimetry (TG) and differential scanning calorimetry (DSC) and their results reported. It was found that for each of the three complexes studied, the starting material M(CO)₆ was formed which immediately sublimed unchanged with or without concomitant loss of carbonyl (CO) ligands to give the first large weight loss step. This was closely followed by the volatilisation of the pyridine ligands and at higher temperatures the loss of further CO ligands. The enthalpy changes associated with the above-mentioned steps are reported. The conversion of M(CO)₅py to M(CO)₆ and other products was confirmed by the analysis of residue after pyrolysis in a tube furnace under conditions similar to those observed in TG experiments.

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Zusammenfassung Der thermische Abbau von drei monosubstituierten Hexacarbonylkomplexen der allgemeinen Formel M(CO)₅py (mit M=Cr, Mo und W; py=Pyridin) wurden mittels TG und DSC untersucht. Von jeder der drei Komplexe wird die Ausgangssubstanz M(CO)₆ erhalten, die sofort unverändert mit oder ohne gleichzeitigem Verlust an Carbonyl (CO)-Liganden sublimiert und die erste große Gewichtsverluststufe ergibt. Diesem Schritt folgt gleich die Verflüchtigung des Pyridinliganden und bei höheren Temperaturen die Abgabe weiterer CO-Liganden. Die mit den genannten Schritten einhergehenden Enthalpieveränderungen werden mitgeteilt. Die Umwandlung von M(CO)₅py zu M(CO)₆ und anderen Produkten wurden durch Analyse des Rückstandes nach der Pyrolyse in einem Röhrenofen unter ähnlichen Bedingungen wie in den TG-Versuchen bestätigt.

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()₅, M=, , =. , , , . , . . , .

     

混合金属氧化物固载杂多酸的制备及催化性能

杂多酸是一类含氧桥的多核无机高分子化合物,由于其独特的笼型结构而具有许多优异的性能,尤其是作为一种新型的多功能催化剂越来越受到人们的关注。因此,近年来人们一直致力于研究新型固载杂多酸催化剂。本文介绍了钛钨混合金属氧化物固载杂多酸催化剂HPA／TiO2-WO3的制备,及催化合成甲酸环己酯的方法,此法具有反应时间短、催化剂价廉易得、工艺简单、酯产率较高等优点。     

Design of supported metal catalysts modified with metal oxides for hydrodeoxygenation of biomass-related molecules

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Heterogenized transition metal complexes as catalysts for synthesizing methylpyridines from acetaldehyde and ammonia

The synthesis of methylpyridines from acetaldehyde and ammonia in the presence of N- and F-containing heterogenized transition metal complexes is studied by a pulse microcatalytic method. A correlation between the donor—acceptor properties of the ligand, of the complexed metal, and of the catalytically active complex is found using ³¹P NMR. The reaction direction depends on the properties of the solvent used to heterogenize the complex on the carrier.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 773–779, June, 1993.     

Manganese‐based transition metal complexes as new catalysts for olefin polymerizations

Three manganese complexes, Mn(acac)₃ (acac = acetylacetonate), Cp₂Mn (Cp = cyclopentadienyl), and Mn(salen)Cl [salen = 1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐dit‐butyl‐salicylidene)], were used for ethylene and propylene polymerizations. These complexes, in combination with an alkylaluminum cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (AlEt₂Cl), could promote ethylene polymerizations that yielded extremely high molecular weight linear polymers, but were inactive for propylene polymerizations. The counterparts supported on MgCl₂ showed activities even for propylene polymerizations and had remarkably enhanced activities for ethylene polymerizations. In the presence of an electron donor such as ethylbenzoate, the MgCl₂‐supported manganese‐based catalysts yielded a highly isotactic polypropylene with a high molecular weight. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3733–3738, 2001     

Silica-alumina supported transition metal oxide catalyst for alkylation of aromatic compounds

Titanium oxide on silica-alumina support is described to be an efficient regenerable catalyst for alkylation of aromatic compounds with alkyl halides, alcohols and olefins, and the reaction is proposed to be initiated by the protonated metal active species present in the catalyst.     

The synthesis of polymer-anchored h3-allylic transition metal complexes and their use as catalysts

Soluble polymers and crosslinked resins containing difluoroacetic side- groups were used as supports for h³-allyl nickel and molybdenum complexes. Both types of anchored complexes in themselves are effective catalysts for the stereospecific polymerization of 1,3 butadiene, while the nickel complex, activated by reaction with aluminium cocatalysts, catalyzes olefin and diolefin hydrogenation and propylene dimerization.     

The reaction of formyl fluoride with transition metal complexes

Formyl fluoride reacts with metal carbonyl anions in a manner similar to acetic formic anhydride. Although formyl complexes may have been formed as unstable intermediates, no neutral formyl complexes could be isolated but rather the expected decomposition products, the metal carbonyl hydrides or ?imers, were produced. The attempted oxidative addition of formyl fluoride to various coordinately unsaturated metal complexes also did not result in the formation of formyl derivatives. HF adducts were obtained from the reaction ?fIr(CO)Cl(PR₃)₂ or M(PPh₃)₄ (M Pt or Pd) with formyl fluoride whereas Ru(NO)Cl(PPh₃)₂ and Rh(PPh₃)₃ Cl give the CO complexes Ru(NO)(CO)Cl(PPh₃)₂ and Rh(CO)Cl(PPh₃)₂, respectively.     

Mechanism of enantioselective Ti-catalyzed Strecker reaction: peptide-based metal complexes as bifunctional catalysts.

Kinetic, structural, and stereochemical data regarding the mechanism of Ti-catalyzed addition of cyanide to imines in the presence of Schiff base peptide ligands are disclosed. The reaction is first order in the Ti-ligand complex; kinetic studies reveal DeltaS(dagger) = -45.6 +/- 4.1 cal K(-1) mol(-1), indicating a highly organized transition structure for the turnover-limiting step of the catalytic cycle. A mechanistic model consistent with the kinetic and stereochemical data is presented, where the Ti center is coordinated to the Schiff base unit of the ligand and the AA2 moiety of the peptidic segment of the chiral ligand associates and delivers HNC to the activated bound substrate. Thus, these studies illustrate that these non-C2-symmetric catalysts likely operate in a bifunctional fashion.     

Tertiary amine oxides as phase transfer catalysts for substitution and dichlorocyclopropanation reactions

Tertiary amine oxides catalyze a variety of phase transfer reactions, primarily by $\text{in}$$\text{situ}$ deoxygenation to form the tertiary amine or derived catalyst.