Phosphabarrelene-rhodium complexes as highly active catalysts for isomerization free hydroformylation of internal alkenes

A new class of phosphabarrelene-rhodium catalysts is described which allows for the first time hydroformylation of internal alkenes with very high activity and which proceeds essentially free of alkene isomerization.     

Soluble polymer-supported ruthenium porphyrin catalysts for epoxidation,cyclopropanation, and aziridination of alkenes

[reaction: see text] Attachment of poly(ethylene glycol) (PEG) to ruthenium porphyrin via a covalent etheric bond gives soluble polymer-supported ruthenium catalysts 3-5. These catalysts exhibit high reactivity and selectivity toward alkene epoxidation with 2,6-dichloropyridine N-oxide and alkene cyclopropanation with diazo compounds. The application of these catalysts in the synthesis of unstable organic compounds has been demonstrated.     

The isomerization equilibrium between cis and trans chloride ruthenium olefin metathesis catalysts from quantum mechanics calculations

The cis-trans chloride isomerization of a ruthenium olefin metathesis catalyst is studied using quantum mechanics (B3LYP DFT), including the Poisson-Boltzmann (PBF) continuum approximation. The predicted geometries agree with experiment. The energies in methylene chloride, lead to DeltaG = -0.70 kcal/mol and a cis:trans ratio of 76:24, quite close to the experimental value of DeltaG = -0.78 kcal/mol or c:t 78:22. In contrast, we predict that in benzene c:t = 4:96 in agreement with the experimental observation of only the trans isomer. Our calculated relative activation energies explain the observed difference in initiation rates and suggest that each isomer should be isolable in high ratio by simply changing solvent.     

Acid catalyzed isomerization of bicyclic alkenes: a facile betweenanene synthesis

Isomerization of $\text{cis}$-bicyclo[10.8.0]eicos-1(12)-ene ($\text{1a}$) and $\text{cis}$-bicyclo[10.10.0]docos-1(12)-ene ($\text{1b}$) to [10.8]- and [10.10]betweenanene ($\text{2a}$ and $\text{2b}$) has been effected by sulfuric acid. In both cases, the betweenanene isomers were found to predominate at equilibrium (70/30 $\text{2a}$/$\text{1a}$ and 95/5> $\text{2b}$/$\text{1b}$).     

New Schiff base complexes of ruthenium(III) and their use as catalysts for O-allyl systems isomerization

Seven new ruthenium(III) complexes of the general formula [RuCl(PPh₃)LL′] · xH₂O (LL′ = [ONNO] = symmetrical and unsymmetrical Schiff base derivatives of trans-1,2-diaminocyclohexane and 2-hydroxynaphthaldehyde as well as R-salicylaldehydes, x = 0–3) have been synthesized. The complexes were characterized by physico-chemical and spectroscopic techniques. The catalytic activities of the complexes in the isomerization reaction of selected O-allyl systems, i.e., 1,4-diallyloxybutane and 4-allyloxybutan-1-ol have been studied. Some of the complexes showed high efficiency and E-stereoselectivity in double bond migration of allyl group to 1-propenyl group and high selectivity of isomerization of allyloxyalcohol to cyclic acetal.     

A novel chelation-assisted hydroesterification of alkenes via ruthenium catalysis

An efficient and catalytic protocol of hydroesterification of alkenes has been developed without a need for CO atmosphere. With the introduction of the 2-pyridyl moiety as a chelating group in formate, Ru3(CO)12-catalyzed activation of the formyl C-H bond of formate and subsequent addition of the intermediate to alkenes proceeded with almost complete suppression of decarbonylation. Stereoselectivity of the produced one-carbon elongated esters was good to excellent for the formation of the linear adduct depending on the bulkiness of the alkenes used. This procedure could be readily applied to a variety of olefins such as terminal, internal, cyclic, bicyclic, vinyl ether, and conjugated enone systems with high efficiency and selectivity. It was also amenable to a solvent-free condition. On the basis of the chelation-driven C-H bond activation of formate, a putative mechanism of the Ru-catalyzed hydroesterification of 2-pyridylmethyl formate has been proposed.     

Mechanism of alkene isomerization by bifunctional ruthenium catalyst: A theoretical study

The molecular mechanism of the isomerization of 1-pentene to form (E)-2-pentene catalyzed by the bifunctional ruthenium catalyst has been investigated using density functional theory calculations. The reaction is likely to proceed through the following steps: 1) the β-H elimination to generate the ruthenium hydride intermediate; 2) the reductive elimination of the hydride intermediate to generate the nitrogen-protonated allyl intermediate; 3) the transportation of the hydrogen by the dihedral rotation with Ru–P bond acting as axis; 4) the oxidative addition to afford another hydride complex; 5) the reductive elimination of the hydride intermediate to form the C₂-C₃ π-coordinated agostic intermediate; 6) the coordination of the nitrogen to the ruthenium center to give the final product. The rate-determining step is the oxidative addition step (the process of the hydrogen moves to ruthenium center from the nitrogen atom) with the free energy of 31.2 kcal/mol in the acetone solvent. And the N-heterocyclic ligand in the catalyst mainly functions in the two aspects: affords an important internal-basic center (nitrogen atom) and works as a transporter of hydrogen. Our results would be helpful for experimentalists to design more effective bifunctional catalysts for isomerization of a variety of heterofunctionalized alkene derivatives.     

Decomposition of ruthenium olefin metathesis catalysts

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H2IMes)(Cl)2Ru=CH(2-C6H4-O-i-Pr) (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H2IMes)(pyridine)3(Cl)2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H2IMes)(pyridine)2(Cl)2Ru=CH2, is also reported.     

Metal complex catalysts immobilized in polymer gels

A number of polymer gels have been prepared using tertiary ethylene‐propylene‐ethylidenenorbomene copolymer as a rubber base with grafted poly‐4‐vinylpyridine, polymethacrylic acid and polymethacrylamide ligand chains. The grafted copolymers were crosslinked and complexes of nickel, zirconium and titanium were immobilized in the formed crosslinked copolymers. After treatment with organoaluminium compounds the obtained catalysts demonstrate high catalytic activity in the reactions of dimerization of lower olefins. Structures of the complexes and the catalytic activity of the gel immobilized catalysts have been investigated.     

Highly efficient epoxidation of cyclic alkenes catalyzed by ruthenium complex

The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.     

Hydrogenation of alkenes catalyzed by supported Ziegler catalysts

Supported Ziegler catalysts prepared by the reaction of a Ni(II) 1-butylsalicylaldiminate or Ni(II) 2-ethylhexanoate with Al₂O₃/SiO₂ treated with AlEt₃ or NaAlH₂ (OCH₂CH₂OCH₃)₂ are efficient catalysts for hydrogenation of simple alkenes. The factors influencing their activity are reported.

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, qp - Ni(II) - Ni(II) 2- Al₂O₃/SiO₂, AlEt₃ NaAlH₂ (OCH₂CH₂OCH₃)₂, . , .

     

Decomposition pathways of Z-selective ruthenium metathesis catalysts

The decomposition of a Z-selective ruthenium metathesis catalyst and structurally similar analogues has been investigated utilizing X-ray crystallography and density functional theory. Isolated X-ray crystal structures suggest that recently reported C-H activated catalysts undergo decomposition via insertion of the alkylidene moiety into the chelating ruthenium-carbon bond followed by hydride elimination, which is supported by theoretical calculations. The resulting ruthenium hydride intermediates have been implicated in previously observed olefin migration, and thus lead to unwanted byproducts in cross metathesis reactions. Preventing these decomposition modes will be essential in the design of more active and selective Z-selective catalysts.     

Gas-phase thermochemistry of ruthenium carbene metathesis catalysts

Quantitative energy-resolved collision-induced dissociation cross-sections by tandem ESI-MS provide absolute thermochemical data for phosphine binding energies in first- and second-generation ruthenium metathesis catalysts of 33.4 and 36.9 kcal/mol, respectively. Furthermore a study of the ring-closing metathesis in the second-generation system to liberate norbornene by forming the 14-electron reactive intermediate from the intramolecular pi-complex gives an estimate of the olefin binding energy to the 14-electron complex of around 18 kcal/mol, assuming a loose transition state. The results reported here are in remarkably good agreement with the latest DFT calculations using the M06-L functional.     

Activation of ruthenium on silica hydrogenation catalysts

Activation of RuCl₃-impregnated silica by nitrogen-hydrogen tratment at high temperature, up to 700 °C, is superior to calcination of the material prior to reduction. Sintering hardly occurs. In addition, activity measurements, based on the liquid phase hydrogenation of benzene, and thermogravimetric analysis suggest a favorable (chemical) interaction between ruthenium and silica.

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, RuCl₃ 700°C . . , , () .

     

Particle size control in dendrimer-derived supported ruthenium catalysts

A high-resolution transmission electron microscopy (HRTEM) investigation of a family of supported Ru catalysts prepared from Ru hydroxyl-terminated poly(amidoamine) dendrimer-metal nanocomposite (DMN) precursors has been conducted. Ru particle sizes observed following deposition of DMNs on a HRTEM grid can be controlled within a 0.9-1.4 nm range depending on the metal-to-dendrimer molar ratio. The average particle size in this case correlates well with the theoretically predicted particle size from the molar loading of Ru in the dendrimer. Upon impregnation of Ru-DMNs on Al(2)O(3) and subsequent thermal removal of the dendrimer via reduction at 300 degrees C, significant sintering of the Ru particles was observed. Nevertheless, the resulting supported Ru particles maintained a narrow particle size distribution and average particle size below 2.5 nm. These particle sizes no longer correlate with the metal-to-dendrimer molar ratio but do correlate with the metal-to-dendrimer weight ratio, suggesting that the dendrimer may be acting as a "sintering-control" agent on the catalyst surface. This process is not affected by the surface area of the support, since almost identical particle size distributions were obtained on three different commercial supports.     

Allylic amination of alkenes by tosyliminoiodobenzene: manganese porphyrins as suitable catalysts

Manganese-porphyrins and particularly Mn(TPP)(ClO₄) were found to be much better catalysts than iron-porphyrins for allylic N-tosylamination of alkenes by tosyliminoiodobenzene. With the former catalysts, cyclohexene was selectively transformed into 3-tosylaminocyclohexene with yields up to 70% and cis- and trans-hex-2-ene into allylic N-tosylamines with yields around 40%, whereas cyclooctene led to the corresponding allylic and homoallylic N-tosylamines.