Oxidative Dehydrodimerization Research Articles

Stereospecific approach to the synthesis of ring-A oxygenated sarpagine indole alkaloids. Total synthesis of the dimeric indole alkaloid P-(+)-dispegatrine and six other monomeric indole alkaloids.

The first regio- and stereocontrolled total synthesis of the bisphenolic, bisquaternary alkaloid (+)-dispegatrine (1) has been accomplished in an overall yield of 8.3% (12 reaction vessels) from 5-methoxy-d-tryptophan ethyl ester (17). A crucial late-stage thallium(III) mediated intermolecular oxidative dehydrodimerization was employed in the formation of the C9-C9' biaryl axis in 1. The complete stereocontrol observed in this key biaryl coupling step is due to the asymmetric induction by the natural sarpagine configuration of the monomer lochnerine (6) and was confirmed by both the Suzuki and the oxidative dehydrodimerization model studies on the tetrahydro β-carboline (35). The axial chirality of the lochnerine dimer (40) and in turn dispegatrine (1) was established by X-ray crystallography and was determined to be P(S). Additionally, the first total synthesis of the monomeric indole alkaloids (+)-spegatrine (2), (+)-10-methoxyvellosimine (5), (+)-lochnerine (6), lochvinerine (7), (+)-sarpagine (8), and (+)-lochneram (11) were also achieved via the common pentacyclic intermediate 16.

Profiling of diferulates (plant cell wall cross-linkers) using ultrahigh-performance liquid chromatography-tandem mass spectrometry

Recalcitrance of grasses to enzymatic digestion arises to a significant degree from a complex array of phenolic crosslinks between cell wall polysaccharide chains that inhibit their conversion to biofuels and lower their nutritive value for animal feed applications. Polysaccharide esters of ferulic acid are abundant in plant cell walls. Crosslinks between polysaccharides are formed through oxidative dehydrodimerization of ferulates, producing dehydrodiferulates (henceforth termed diferulates). Such ferulates and diferulates further crosslink plant cell walls by radical coupling cross-reactions during lignification. Although cell wall digestibility can be improved by cell wall metabolic engineering, or post-harvest by various pretreatment processes, a more comprehensive understanding of the role and impact of ferulate crosslinking on polysaccharide hydrolysis would be accelerated by availability of analytical methods that can distinguish the various diferulates released during biomass pretreatments, many of which are isomers. In this report, we present an ultrahigh-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) strategy for comprehensive separation and identification of diferulate isomers. Collision-induced dissociation (CID) mass spectra of [M + H](+) ions distinguished various isomers without requiring derivatization. Characteristic product ions for 8-O-4-, 8-8-non-cyclic, 8-8-cyclic, 8-5-cyclic, 8-5-non-cyclic, and 5-5-linked isomers were identified. All diferulates were identified either as di-acids in extracts of NaOH-hydrolyzed corn stover, or as a diverse group of diferulate mono- and di-amides in extracts of Ammonia Fiber Expansion (AFEX™)-treated corn stover. This approach allows for direct analysis of released diferulates with minimal sample preparation, and can serve as the foundation for high-throughput profiling and correlating pretreatment conditions with biomass digestibility in biorefineries producing biofuels and biochemicals.

Features of the mechanism of oxidative dehydrodimerization of propynol

Analysis of kinetic regularities for the propynol oxidative coupling under the action of cupric salts in pyridine and in the presence of a buffer is undertaken. The reaction mechanism, including the formation of Cu(I) acetylides, is considered.

Redox induced reactions of transition metal π- and σ,π-complexes

In this review, redox-induced reactions of π- and σ,π-complexes leading to the selective formation (or cleavage) of C–H, C–C, and C–O bonds have been summarized. To illustrate the synthetic potential of such methodology, the following representative reactions studied in our group are discussed: (1) oxidatively induced hydrogen elimination from “open” cyclic diene and dienyl complexes resulting in formation of “closed” dienyl and arene complexes, respectively; (2) reductive activation of C–H bonds in diene, vinylidene, and carbyne complexes forming new multiple C–C bonds; (3) oxidative dehydrodimerization of vinylidene complexes into binuclear μ-divinylidene species; and (4) oxidatively induced addition of oxygen nucleophiles to μ-divinylidene complexes affording cyclic μ-dicarbene derivatives.

Dehydrodimerization of Isobutene to 2,5‐Dimethyl‐1,5‐Hexadiene over Bismuth‐(III)‐Oxide and Various Additives

AbstractBi2O3 and mixtures with different additives (Cr2O3, MoO3, NH4VO3, SnO2, and V2O5) have been chosen to study the oxidative dehydrodimerization of isobutene. The catalytic performances were investigated by variation of the residence time, isobutene to oxygen molar ratio, and pressure. The best results for 2,5‐dimethyl‐1,5‐hexadiene (DMH) yield (13 %) were achieved with Bi2O3 as the catalyst. The selectivity of DMH reaches values of over 90 %.

Oxidative dehydrodimerization of rhenium vinylidene complex (η 5-C 5H 5)(CO) 2Re [dbnd]C [dbnd]C(H)Ph: two competitive routes of coupling of σ-phenylethynyl intermediate [(η 5-C 5H 5)(CO) 2Re [sbnd]C [tbnd]CPh] [rad]. X-ray structures of rhenium mononuclear (η 5-C 5H 5)(CO) 2Re [dbnd]C [dbnd]C(H)Ph and binuclear [(η 5-C 5H 5)(CO) 2Re] 2(μ 2-C [dbnd]C(Ph)C [tbnd]CPh) vinylidene compounds

The oxidation of the rhenium vinylidene complex (η 5-C 5H 5)(CO) 2Re C C(H)Ph ( 2) with one equivalent of AgBF 4 or (C 5H 5) 2FeBF 4 leads to the radical cation [(η 5-C 5H 5)(CO) 2Re C C(H)Ph] + ( 2 + ) which undergoes dehydrodimerization only in the presence of triethylamine affording a mixture of the binuclear compounds (η 5-C 5H 5)(CO) 2Re C C(Ph)C(Ph) C Re(CO) 2(η 5-C 5H 5) ( 6, 55%) and [(η 5-C 5H 5)(CO) 2Re] 2(μ 2-C C(Ph)C CPh) ( 9, 22%). Both 6 and 9 are believed to arise via competitive C β–C β and C β–Re couplings of the intermediate σ-phenylethynyl radicals [(η 5-C 5H 5)(CO) 2Re C CPh] ( 5 ). The former process directly yields 6and the latter one produces 9 after reductive elimination and a 1,2-shift of the metal containing moiety. The enthalpies of C β–C β (−30.3 kcal/mol) and C β–Re (+0.3 kcal/mol) coupling processes estimated by DFT calculations are in accordance with the 6: 9 ratio observed. The electrochemical behavior of 2, 6, 9 was studied by cyclic voltammetry. The X-ray structures of 2 and 9 are reported.

Relative reactivity of hydrocarbons in oxidative dehydrodimerization

Oxidative transformations of olefins (ethylene, propylene, isobutylene) and aromatics (benzene, toluene) were studied on oxide catalysts. A requirement for hydrocarbons taking part in oxidizing dehydrodimerization is the presence of a mobile hydrogen atom ..cap alpha.. to the unsaturated bond. The relative reactivity of hydrocarbons is determined by the mobility of allyl type surface compounds and their bonding strength with the catalyst. 12 references, 2 tables.

Oxidative dehydrodimerization of toluene on lead-tin oxide catalysts

Oxidative dehydrodimerization of toluene on lead-tin oxide catalysts

Study of Redox-induced Reactions of Vinylidene and bis-Vinylidene Complexes of Manganese

Oxidative dehydrodimerization of some phenylvinylidene complexes of manganese is studied by cyclic voltammetry. In the case of (η5-C5H5)(CO)2Mn=C=C(H)Ph, the process occurs as the homolysis of the Cβ–H bond in the radical cation of {(η5-C5H5)(CO)2Mn=C=C(H)Ph}+· and the dimerization of intermediate σ-phenylethinyl cation [(η5-C5H5)(CO)2Mn–C≡C–Ph]+ to a binuclear dication of bis-carbine type (η5-C5H5)(CO)2Mn+≡C– C(Ph)=C(Ph)–C≡Mn+(CO)2(η5-C5H5). The reduction of the latter leads to binuclear bis-vinylidene complex (η5-C5H5)(CO)2Mn=C=C(Ph)–C(Ph)=C=Mn(CO)2(η5-C5H5). Oxidative dehydrodimerization of complexes (η5-C5R5)(CO)(L)Mn=C=C(H)Ph (R = H, L = PPh3; R = Me, L = CO) occurs through the immediate Cβ–Cβ coupling of radical cations {(η5-C5R5)(CO)(L)Mn=C=C(H)Ph}+· and yields binuclear dication bis-carbine complexes (η5-C5R5)(CO)(L)Mn+≡C–C(H)(Ph)–C(H)(Ph)–C≡Mn+(CO)(L)(η5-C5R5), whose reduction leads to neutral compounds (η5-C5H5)(CO)2Mn=C=C(Ph)–C(Ph)=C=Mn(CO)(L)(η5-C5H5). Complex (η5-C5H5)(CO)2Mn=C=C(Ph)–C(Ph)=C=Mn(CO)2(η5-C5H5) undergoes the oxidation-induced nucleophilic addition of water, forming cyclic bis-carbene product with a bridge heterocyclic ligand (μ-3,4-diphenyl-2,5-dihydro-2,5-diylidene)-bis-(η5-cyclopentadienyldicarbonyl manganese).

Oxidative dehydrodimerization of manganese vinylidene complexes (η5‐C5R5)(CO)(L)MnCCHPh (R = Me, L = CO; R = H, L = PPh3)

AbstractThe oxidative dehydrodimerization of the phenylvinylidene manganese complexes (η5‐C5R5)(CO)(L)MnCCHPh (5: R=Me, L=CO; 6: R=H, L=PPh3) into the corresponding bis‐vinylidene compounds (η5‐C5R5)(CO)(L)MnCCPhCPhCMn(CO)(L)(η5‐C5R5) (7: R=Me, L=CO; 8: R=H, L=PPh3) was studied by cyclic voltammetry and chemical experiments. It was found that dehydrodimerization of 5 and 6 proceeds via direct C(β)C(β) coupling of the radical cations 5 +· and 6 +· to give dicationic bis‐carbyne complexes [(η5‐C5R5)(CO)(L)Mn≡CCPhHCPhHC≡Mn(CO)(L)(η5‐C5R5)]2+ (10 ++: R=Me, L=CO; 11 ++: R=H, L=PPh3), which can be converted into bis‐vinylidene complexes 7 and 8 respectively by reduction with (η‐C6H6)2Cr. In this process, binuclear 19‐electron bis‐carbyne compounds 10 ·· and 11 ·· undergo further transformation into the dimers 7 and 8 via homolysis of C(β)H bonds of the bis‐carbyne ligand, thus exhibiting rare examples of reductive activation of CH bonds in 19‐electron transition metal carbyne complexes. Copyright © 2002 John Wiley & Sons, Ltd.

Oxidative Dehyrodimerization of Methane Using Manganese-based Catalysts Made by Self-propagating High-temperature Combustion Synthesis

The self-propagating high-temperature synthesis (SHS) method has been used to produce a range of active manganese-based catalysts for the oxidative dehydrodimerization of methane. Catalytic activity was measured at temperatures between 920 and 1120 K under a range of conditions. In the best case found, the ethylene yield reached about 26 % with a selectivity of 85 % and a methane conversion of 30.2 %. Some ethane, propylene, propane and hydrogen were also obtained. The addition of alkaline elements, promoted by halides, increased the yield of ethylene at the expense of reduced stability. The catalytic activity was found to be enhanced by careful control of SHS conditions and various post-synthesis treatments of the materials.

ChemInform Abstract: Oxidation of Aromatic Compounds. Part 8. Oxidative Dehydrodimerization of Cinnamic Acid Derivatives in the System CF3COOH—CH2Cl2—PbO2.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Oxidative dehydrodimerization of manganese phenylvinylidene complex (η 5-C 5H 5)(CO) 2MnCC(H)Ph. X-ray structure of phenyl(trityl)vinylidene complex (η 5-C 5H 5)(CO) 2MnCC(CPh 3)Ph

The oxidatively induced dehydrodimerization of the manganese vinylidene complex (η 5-C 5H 5)(CO) 2MnCC(H)Ph ( I) to the bis-vinylidene compound (η 5-C 5H 5)(CO) 2MnCC(Ph)C(Ph)CMn(CO) 2(η 5-C 5H 5) ( II) proceeds via C βH bond homolysis in the radical cation ( I + ) and is thought to involve the formally 16-electron mononuclear σ-phenylethynyl cation [(η 5-C 5H 5)(CO) 2MnCCPh] + ( III) and the bis-carbyne dication [(η 5-C 5H 5)(CO) 2MnCC(Ph)C(Ph)CMn(CO) 2(η 5-C 5H 5)] 2+ ( II 2+) as the key sequential intermediates. Compound II 2+ was characterized by IR and CV. The reduction of II 2+ with (C 6H 6) 2Cr gave II in an 80% yield. Compound II can be prepared more conveniently by treating I with (C 5H 5) 2FeBF 4 in the presence of Et 3N. The interaction of I with Ph 3CPF 6 yields the trityl(phenyl)vinylidene complex (η 5-C 5H 5)(CO) 2MnCC(CPh 3)Ph ( IV) as a result of the electrophilic attack of the trityl cation on C β followed by the loss of a proton. The structure of IV was established by an X-ray structural analysis.

Oxidative dehydrodimerization of methane using lead and samarium-based catalysts made by self-propagating high-temperature synthesis

The self-propagating high-temperature synthesis (SHS) method has been used to produce a range of active catalysts based on lead and samarium for the oxidative dehydrodimerization of methane. Catalytic activity was measured at temperatures between 920 and 1120 K under various conditions and various oxides of lead and samarium were found to be active for this process. Ethene yield was found to reach about 20 wt.% (with a selectivity of 88% at a conversion of 24.7%) but the process yielded also significant quantities of ethane, propene, propane and hydrogen. Depending on conditions, methane conversion was found to reach up to 24%. The catalytic activity can be enhanced by varying the synthesis conditions and further treatment after production of the materials. In particular, the porosity needs to be improved substantially.

First synthesis of mastigophorenes A and B, by biomimetic oxidative coupling of herbertenediol

The first synthesis of mastigophorenes A and B by oxidative phenolic coupling of partially protected derivatives of their joint natural monomeric half, herbertenediol, is described. The synthesis starts from this diol itself or from the corresponding aldehyde, both available by isolation from the liverwort, Herbertus aduncus. After transformation of herbertenediol to a chemically appropriate monophenolic coupling precursor, the oxidative dehydrodimerization was brought about using ( tert-BuO) 2, followed by deprotection to give mastigophorenes A and B in their ‘natural’ atropisomeric ratio, as isolated from the liverwort.

Oxidative dehydrodimerization of methane on Bi-Mn oxides: Catalyst active component and reaction mechanism

A series of Bi-Mn-O catalysts has been studied as a function of bismuth content (from 0 to 100 atom.%). The fresh-prepared samples are found to be a heterophasic mixture of the Bi 2Mn 4O 10 compound with the individual manganese or bismuth oxide, the surface of which is enriched in bismuth. At initial period of catalytic work, a part of Bi 2Mn 4O 10 decomposes to ga-Bi 2O 3 and α-Mn 2O 3 resulting in the formation of rather effective catalyst for methane oxidative coupling. It is postulated that the catalyst active component consists of a Bi 2O 3 phase lying at the surface of a Bi 2Mn 4O 10 compound. At a steady state, the oxidative dehydrodimerization reaction occurs via both redox and associative mechanisms whilst the deep oxidation proceeds mainly according to the redox one.

Oxidative dehydrodimerization of methane over complex oxide catalysts prepared by self-propagating high-temperature synthesis

Oxidative dehydrodimerization of methane to C 2 - hydrocarbons has been examined for complex oxide ceramics prepared by using method of self-propagating high-temperature synthesis (SHS) in a combustion mode. The novel catalysts containing rare-earth, alkali-earth metals and copper showed sufficiently high level of activity, C 2 selectivity and stability in the presence of oxygen at temperature 700–800C, atmospheric pressure, the mole ratio CH 4/O 2= 5–8 and contact time 0.6–9.0 s.

Temperature programmed reduction studies on phase reconstruction of Na2O−MnOx-catalysts for the oxidative dehydrodimerization of methane

The change in phase composition and integral oxidation state of Na2O−MnOx-catalysts caused by simultaneous air and methane interaction was studied using Temperature Programmed Reduction. Sodium manganates (III, IV) continue to exist during catalytic reaction whereas sodium manganate (V) decomposes.

Structure and catalytic properties of samarium-calcium oxide catalysts in methane oxidative dehydrodimerization

Synthesis of samarium-calcium oxide catalysts has been studied. Conditions for obtaining systems that contain cubic, monoclinic and mixture of two forms of samarium oxide have been found. The catalyst with two Sm2O3 forms has been shown to be the most active and selective towards oxidative dehydrodimerization of methane. Electrical conductivity over samarium-calcium catalysts have been studied. It is concluded that high selectivity and activity of the samples with two Sm2O3 forms are due to high mobility of oxygen vacancies.

Type of hydrocarbon activation and nature of active sites of base catalysts in methane oxidative dehydrodimerization

Methane activation on magnesium-oxide-cased catalysts for methane dehydrodimerization has been studied. As found, the rate of dehydrodimerization changes proportionally with the concentration of base sites on the catalytic surface. The activation of methane results in the formation of the methyl anion, as ascertained by IR-Fourier spectroscopy. The dehydrodimerization rates have been compared with the concentration of one-electron sites and the rate of the CH 4CD 4 isotope exchange. Based on the data obtained a new mechanism of methane dehydrodimerization has been proposed; at the first reaction step a fast heterolytic dissociation of methane on base sites takes place. The rate-determining step is that of the metal-methyl dissociation leading to the formation of the methyl radical which determines a high activation energy of methane dehydrodimerization on oxide catalysts.