Alkane Activation Research Articles

Discovery of Methylaluminoxane as Cocatalyst for Olefin Polymerization

The discovery of methylaluminoxane (MAO) was the start for investigations and innovations of new classes of highly active olefin polymerization catalysts. Different transition metal complexes together with MAO as cocatalyst allow the synthesis of polymers with a highly defined microstructure, tacticity, and stereoregularity as well as new cycloolefin, long chain branched, or blocky copolymers with excellent properties. These new polyolefins could not be obtaind with such a purity before by Ziegler–Natta catalysts. The single site catalyst character of metallocene and other transition metal complexes activated by MAO leads to a better understanding of the mechanism of the olefin polymerization.

ChemInform Abstract: C—H Activation of Alkanes in Selective Oxidation Reactions on Solid Oxide Catalysts

AbstractReview: 105 refs.

ChemInform Abstract: Results of NMR Spectroscopic Studies of Hydrocarbon Conversions on Solid Acid Catalysts in the Last 25 Years

AbstractReview: 86 refs.

Selective Homogeneous and Heterogeneous Catalytic Conversion of Methanol/Dimethyl Ether to Triptane

The demand for specific fuels and chemical feed-stocks fluctuates, and as a result, logistical mismatches can occur in the supply of their precursor raw materials such as coal, biomass, crude oil, and methane. To overcome these challenges, industry requires a versatile and robust suite of conversion technologies, many of which are mediated by synthesis gas (CO + H(2)) or methanol/dimethyl ether (DME) intermediates. One such transformation, the conversion of methanol/DME to triptane (2,2,3-trimethylbutane) has spurred particular research interest. Practically, triptane is a high-octane, high-value fuel component, but this transformation also raises fundamental questions: how can such a complex molecule be generated from such a simple precursor with high selectivity? In this Account, we present studies of this reaction carried out in two modes: homogeneously with soluble metal halide catalysts and heterogeneously over solid microporous acid catalysts. Despite their very different compositions, reaction conditions, provenance, and historical scientific context, both processes lead to remarkably similar products and mechanistic interpretations. In both cases, hydrocarbon chains grow by successive methylation in a carbocation-based mechanism. The relative rates of competitive processes-chain growth by methylation, chain termination by hydrogen transfer, isomerization, and cracking-systematically depend upon the structure of the various hydrocarbons produced, strongly favoring the formation of the maximally branched C(7) alkane, triptane. The two catalysts also show parallels in their dependence on acid strength. Stronger acids exhibit higher methanol/DME conversion but also tend to favor chain termination, isomerization, and cracking relative to chain growth, decreasing the preference for triptane. Hence, in both modes, there will be an optimal range: if the acid strength is too low, activity will be poor, but if it is too high, selectivity will be poor. A related reaction, the methylative homologation of alkanes, offers the possibility of upgrading low-value refinery byproducts such as isobutane and isopentane to more valuable gasoline components. With the addition of adamantane, a hydride transfer catalyst that promotes activation of alkanes, both systems effectively catalyze the reaction of methanol/DME with lighter alkanes to produce heavier ones. This transformation has the further advantage of providing stoichiometric balance, whereas the stoichiometry for conversion of methanol/DME to alkanes is deficient in hydrogen and requires rejection of excess carbon in the form of carbon-rich arenes, which lowers the overall yield of desired products. Alternatively, other molecules can serve as sacrificial sources of hydrogen atoms: H(2) on heterogeneous catalysts modified by cations that activate it, and H(3)PO(2) or H(3)PO(3) on homogeneous catalysts. We have interpreted most of the features of these potentially useful reactions at a highly detailed level of mechanistic understanding, and we show that this interpretation applies equally to these two widely disparate types of catalysts. Such approaches can play a key role in developing and optimizing the catalysts that are needed to solve our energy problems.

ChemInform Abstract: Triphenylphosphine‐Catalyzed [3 + 2] Cycloaddition of Allenoate and Active Olefins: Synthesis of Spirooxindole Derivatives.

AbstractThe process proceeds with complete regioselectivity and allows the application in medicinal chemistry.

Recent development in in situ NMR study on heterogeneous catalysis: mechanisms of light alkane functionalisation

In situ NMR studies of C(1)-C(5) light alkane activation and functionalisation in heterogeneous catalytic systems are overviewed. The results obtained from the NMR technique, particularly those quantitative ones, provide unique information on the activation of alkane molecules and the nature of relevant intermediates, leading to better understanding reaction mechanisms and designing catalysts.

Synthesis of nitrocyclopropanedicarboxylic acid derivatives by addition of α-bromonitroalkanes to methylidene malonic, methylidene cyanoacetic or maleic acid derivatives

A potassium carbonate promoted addition of 2-bromonitroalkanes to methylidenemalonic and methylidenecyanoacetic acid derivatives and N-benzylmaleimide leads to the functionalized nitrocyclopropanes. In the case of less active olefins, it is reasonable to use the phase-transfer catalyst Bu4NPF6 (10 mol.%), whereas in the case of N-benzylmaleimide, to carry out the process in the ionic liquid [bmim]BF4.

Influence of acid strength on the reactivity of alkane activation on solid acid catalysts: A theoretical calculation study

The influence of Brønsted acid strength on the reactivities of alkane activations has been systematically studied by density functional theory (DFT) calculations. Some typical reactions, such as methane hydrogen exchange (C–H bond activation), propane dehydrogenation (C–H bond dissociation and H–H bond formation), and propane cracking (C–C cleavage), were investigated on 8T solid acid models with varying acid strengths from weak-, strong-, to super-acid. According to our calculational results, it was revealed that the activation barriers ( E act) of all the reactions decrease linearly, while the rate coefficients (log k) increase linearly with increasing the acid strength, being indicative of the enhancement of reactivities. However, the reactivity of different reactions exhibits different sensitivity to acid strength: the propane cracking is most sensitive to acid strength, while the methane hydrogen exchange reaction is least sensitive to acid strength. On the basis of the natural charge on the organic fragment in the transition state, it was revealed that the sensitivity of the reactivity to acid strength could be related to the ionic character of the transition state. The propane cracking reaction possesses a more ionic transition state (0.913–0.964 |e|), while the methane hydrogen exchange has a less ionic transition state (0.646–0.773 |e|).

Identification of a potent and selective σ1 receptor agonist potentiating NGF-induced neurite outgrowth in PC12 cells

Herein we report the synthesis, drug-likeness evaluation, and in vitro studies of new sigma (σ) ligands based on arylalkenylaminic scaffold. For the most active olefin the corresponding arylalkylamine was studied. Novel arylalkenylamines generally possess high σ1 receptor affinity (Ki values <25nM) and good σ1/σ2 selectivity (Kiσ2 >100). Particularly, the piperidine derivative (E)-17 and its arylalkylamine analog (R,S)-33 were observed to be excellent σ1 receptor ligands (Ki=0.70 and 0.86nM, respectively) and to display significantly high selectivity over σ2, μ-, and κ-opioid receptors and phencyclidine (PCP) binding site of the N-methyl-d-aspartate (NMDA) receptors. Moreover in PC12 cells (R,S)-33 promoted the nerve growth factor (NGF)-induced neurite outgrowth and elongation. Co-administration of the selective σ1 receptor antagonist BD-1063 totally counteracted this effect, confirming that σ1 receptors are involved in the (R,S)-33 modulation of the NGF effect in PC12 cells and suggesting a σ1 agonist profile. As a part of our work, a threedimensional σ1 pharmacophore model was also developed employing GALAHAD methodology. Only active compounds were used for deriving this model. The model included two hydrophobes and a positive nitrogen as relevant features and it was able to discriminate between molecules with and without affinity toward σ1 receptor subtype.

The Roles of Entropy and Enthalpy in Stabilizing Ion-Pairs at Transition States in Zeolite Acid Catalysis

Acidic zeolites are indispensable catalysts in the petrochemical industry because they select reactants and their chemical pathways based on size and shape. Voids of molecular dimensions confine reactive intermediates and transition states that mediate chemical reactions, stabilizing them by van der Waals interactions. This behavior is reminiscent of the solvation effects prevalent within enzyme pockets and has analogous consequences for catalytic specificity. Voids provide the "right fit" for certain transition states, reflected in their lower free energies, thus extending the catalytic diversity of zeolites well beyond simple size discrimination. This catalytic diversity is even more remarkable because acid strength is essentially unaffected by confinement among known crystalline aluminosilicates. In this Account, we discuss factors that determine the "right fit" for a specific chemical reaction, exploring predictive criteria that extend the prevailing discourse based on size and shape. We link the structures of reactants, transition states, and confining voids to chemical reactivity and selectivity. Confinement mediates enthalpy-entropy compromises that determine the Gibbs free energies of transition states and relevant reactants; these activation free energies determine turnover rates via transition state theory. At low temperatures (400-500 K), dimethyl ether carbonylation occurs with high specificity within small eight-membered ring (8-MR) voids in FER and MOR zeolite structures, but at undetectable rates within larger voids (MFI, BEA, FAU, and SiO(2)-Al(2)O(3)). More effective van der Waals stabilization within 8-MR voids leads to lower ion-pair enthalpies but also lower entropies; taken together, carbonylation activation free energies are lower within 8-MR voids. The "right fit" is a "tight fit" at low temperatures, a consequence of how temperature appears in the defining equation for Gibbs free energy. In contrast, entropy effects dominate in high-temperature alkane activation (700-800 K), for which the "right fit" becomes a "loose fit". Alkane activation turnovers are still faster on 8-MR MOR protons because these transition states are confined only partially within shallow 8-MR pockets; they retain higher entropies than ion-pairs fully confined within 12-MR channels at the expense of enthalpic stability. Selectivities for n-alkane dehydrogenation (relative to cracking) and isoalkane cracking (relative to dehydrogenation) are higher on 8-MR than 12-MR sites because partial confinement preferentially stabilizes looser ion-pair structures; these structures occur later along reaction coordinates and are higher in energy, consistent with Marcus theory for charge-transfer reactions. Enthalpy differences between cracking and dehydrogenation ion-pairs for a given reactant are independent of zeolite structure (FAU, FER, MFI, or MOR) and predominantly reflect the different gas-phase proton affinities of alkane C-C and C-H bonds, as expected from Born-Haber thermochemical cycles. These thermochemical relations, together with statistical mechanics-based treatments, predict that rotational entropy differences between intact reactants and ion-pair transition states cause intrinsic cracking rates to increase with n-alkane size. Through these illustrative examples, we highlight the effects of reactant and catalyst structures on ion-pair transition state enthalpies and entropies. Our discussion underscores the role of temperature in mediating enthalpic and entropic contributions to free energies and, in turn, to rates and selectivities in zeolite acid catalysis.

Triphenylphosphine-Catalyzed [3+2] Cycloaddition of Allenoate and Active Olefins: Syntheses of Spirooxindole Derivatives

A series of spiro compounds was achieved by triphenylphosphine-catalyzed [3+2] cycloaddition between active methylenemalononitrile and ethyl 2,3-butadienoate. Careful investigation showed that the present method had high regioselectivity. The products have a spirooxindole skeleton, which is a motif common in many natural products and pharmaceutically active compounds.

Synthesis of Novel Poly(ethyleneglycol)-400 Ionic Liquid and Its Application in Morita–Baylis–Hillman Reaction

Novel Poly(ethyleneglycol)-400 ionic liquid containing imidazolium cations have been synthesized by the atom-efficient reaction of 1,2-dimethylimidazole with p-toluenesulfonate; the p-toluenesulfonate provides the anionic component of the resultant ionic liquid. It have been used for the first time as a new solvent for the Morita–Baylis–Hillman reaction under ambient conditions. A wide variety of aldehydes and active olefins participate very efficiently, resulting in good to excellent yields of products.

The genome sequence of Desulfatibacillum alkenivorans AK‐01: a blueprint for anaerobic alkane oxidation

Desulfatibacillum alkenivorans AK-01 serves as a model organism for anaerobic alkane biodegradation because of its distinctive biochemistry and metabolic versatility. The D. alkenivorans genome provides a blueprint for understanding the genetic systems involved in alkane metabolism including substrate activation, CoA ligation, carbon-skeleton rearrangement and decarboxylation. Genomic analysis suggested a route to regenerate the fumarate needed for alkane activation via methylmalonyl-CoA and predicted the capability for syntrophic alkane metabolism, which was experimentally verified. Pathways involved in the oxidation of alkanes, alcohols, organic acids and n-saturated fatty acids coupled to sulfate reduction and the ability to grow chemolithoautotrophically were predicted. A complement of genes for motility and oxygen detoxification suggests that D. alkenivorans may be physiologically adapted to a wide range of environmental conditions. The D. alkenivorans genome serves as a platform for further study of anaerobic, hydrocarbon-oxidizing microorganisms and their roles in bioremediation, energy recovery and global carbon cycling.

ChemInform Abstract: Atom‐Economical Synthesis of Unsymmetrical Ketones Through Photocatalyzed C—H Activation of Alkanes and Coupling with CO and Electrophilic Alkenes.

ChemInformVolume 42, Issue 21 Isocyclic Compounds ChemInform Abstract: Atom-Economical Synthesis of Unsymmetrical Ketones Through Photocatalyzed C—H Activation of Alkanes and Coupling with CO and Electrophilic Alkenes. Ilhyong Ryu, Ilhyong Ryu Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorAkihiro Tani, Akihiro Tani Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorTakahide Fukuyama, Takahide Fukuyama Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorDavide Ravelli, Davide Ravelli Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorMaurizio Fagnoni, Maurizio Fagnoni Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorAngelo Albini, Angelo Albini Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this author Ilhyong Ryu, Ilhyong Ryu Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorAkihiro Tani, Akihiro Tani Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorTakahide Fukuyama, Takahide Fukuyama Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorDavide Ravelli, Davide Ravelli Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorMaurizio Fagnoni, Maurizio Fagnoni Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this authorAngelo Albini, Angelo Albini Dep. Chem., Grad. Sch. Sci., Osaka Prefect. Univ., Osaka 599, JapanSearch for more papers by this author First published: 28 April 2011 https://doi.org/10.1002/chin.201121061Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume42, Issue21May 24, 2011 RelatedInformation

ChemInform Abstract: Highly Efficient Oxidative Bromination of Alkanes with the HBr‐H2O2 System in the Presence of Catalyst.

AbstractThe economical, environmentally friendly title system represents a green method for the C‐H bond activation of alkanes.

Alkane degradation under anoxic conditions by a nitrate‐reducing bacterium with possible involvement of the electron acceptor in substrate activation

Microorganisms can degrade saturated hydrocarbons (alkanes) not only under oxic but also under anoxic conditions. Three denitrifying isolates (strains HxN1, OcN1, HdN1) able to grow under anoxic conditions by coupling alkane oxidation to CO2 with NO3− reduction to N2 were compared with respect to their alkane metabolism. Strains HxN1 and OcN1, which are both Betaproteobacteria, utilized n-alkanes from C6 to C8 and C8 to C12 respectively. Both activate alkanes anaerobically in a fumarate-dependent reaction yielding alkylsuccinates, as suggested by present and previous metabolite and gene analyses. However, strain HdN1 was unique in several respects. It belongs to the Gammaproteobacteria and was more versatile towards alkanes, utilizing the range from C6 to C30. Neither analysis of metabolites nor analysis of genes in the complete genome sequence of strain HdN1 hinted at fumarate-dependent alkane activation. Moreover, whereas strains HxN1 and OcN1 grew with alkanes and NO3−, NO2− or N2O added to the medium, strain HdN1 oxidized alkanes only with NO3− or NO2− but not with added N2O; but N2O was readily used for growth with long-chain alcohols or fatty acids. Results suggest that NO2− or a subsequently formed nitrogen compound other than N2O is needed for alkane activation in strain HdN1. From an energetic point of view, nitrogen–oxygen species are generally rather strong oxidants. They may enable enzymatic mechanisms that are not possible under conditions of sulfate reduction or methanogenesis and thus allow a special mode of alkane activation.

A Regioselective Biocatalyst for Alkane Activation under Mild Conditions

Going green: Chemical methods for the hydroxylation of alkanes involve toxic, dangerous reagents and are not very selective. In a biochemical alternative route based on an artificial self-sufficient cytochrome P450, the highly selective and efficient terminal hydroxylation of n-alkanes is possible under mild conditions (see scheme; NADPH is the reduced form of nicotinamide adenine dinucleotide phosphate (NADP+)).

A Regioselective Biocatalyst for Alkane Activation under Mild Conditions

A Regioselective Biocatalyst for Alkane Activation under Mild Conditions

Atom‐Economical Synthesis of Unsymmetrical Ketones through Photocatalyzed CH Activation of Alkanes and Coupling with CO and Electrophilic Alkenes

Atom‐Economical Synthesis of Unsymmetrical Ketones through Photocatalyzed CH Activation of Alkanes and Coupling with CO and Electrophilic Alkenes

Atom‐Economical Synthesis of Unsymmetrical Ketones through Photocatalyzed CH Activation of Alkanes and Coupling with CO and Electrophilic Alkenes

Atom‐Economical Synthesis of Unsymmetrical Ketones through Photocatalyzed CH Activation of Alkanes and Coupling with CO and Electrophilic Alkenes