1632-99-1Relevant academic research and scientific papers
Photoinduced ethane formation from reaction of ethene with matrix-isolated Ti, V, or Nb atoms
Thompson, Matthew G.K.,Parnis, J. Mark
, p. 9465 - 9470 (2005)
The reactions of matrix-isolated Ti, V, or Nb atoms with ethene (C 2H4) have been studied by FTIR absorption spectroscopy. Under conditions where the ethene dimer forms, metal atoms react with the ethene dimer to yield matrix-isolated ethane (C2H6) and methane. Under lower ethene concentration conditions (～1:70 ethene/ Ar), hydridic intermediates of the types HMC2H3 and H2MC 2H2 are also observed, and the relative yield of hydrocarbons is diminished. Reactions of these metals with perdeuterioethene, and equimolar mixtures of C2H4 and C2D 2, yield products that are consistent with the production of ethane via a metal atom reaction involving at least two C2H4 molecules. The absence of any other observed products suggests the mechanism also involves production of small, highly symmetric species such as molecular hydrogen and metal carbides. Evidence is presented suggesting that ethane production from the ethene dimer is a general photochemical process for the reaction of excited-state transition-metal atoms with ethene at high concentrations of ethene.
Differential Reduction of CO2 by Molybdenum and Vanadium Nitrogenases
Rebelein, Johannes G.,Hu, Yilin,Ribbe, Markus W.
, p. 11543 - 11546 (2014)
The molybdenum and vanadium nitrogenases are two homologous enzymes with distinct structural and catalytic features. Previously, it was demonstrated that the Vnitrogenase was nearly 700 times more active than its Mo counterpart in reducing CO to hydrocarbons. Herein, a similar discrepancy between the two nitrogenases in the reduction of CO2 is reported, with the Vnitrogenase being capable of reducing CO2 to CO, CD4, C2D4, and C2D6, and its Mocounterpart only capable of reducing CO2 to CO. Furthermore, it is shown that the Vnitrogenase may direct the formation of CD4 in part via CO2-derived CO, but that it does not catalyze the formation of C2D4 and C2D6 along this route. The exciting observation of a Vnitrogenase-catalyzed C-C coupling with CO2 as the origin of the building blocks adds another interesting reaction to the catalytic repertoire of this unique enzyme system. The differential activities of the V and Monitrogenases in CO2 reduction provide an important framework for systematic investigations of this reaction in the future.
Intermolecular methyl group exchange and reversible P-Me bond cleavage at cobalt(III) dimethyl halide species
Xu, Hongwei,Williard, Paul G.,Bernskoetter, Wesley H.
, p. 798 - 806 (2013)
The cobalt(III) dimethyl halide complexes cis,mer-(PMe3) 3Co(CH3)2X (X = Cl, I) were found to undergo a degenerate cobalt-to-cobalt transfer of the methyl ligands during isotopic labeling experiments. Extensive mechanistic studies exclude radical, methyl iodide elimination, and disproportionation/comproportionation pathways for exchange of the methyl groups between metals. A related cobalt(III) dimethyl complex supported by the tridentate phosphine ligand MeP(CH2CH 2PMe2)2 showed dramatically slower methyl ligand transfer, indicative of a mechanism for intermetallic exchange with a requisite phosphine dissociation. Crossover experiments between cobalt(III) dimethyl halide complexes supported by PMe3 and MeP(CH 2CH2PMe2)2 are consistent with a dicobalt transition structure in which only one cobalt center requires phosphine dissociation prior to methyl transfer. An additional methyl group scrambling process between cis,mer-(PMe3)3Co(CH3) 2I and free PMe3 was also identified during the investigation and originates from reversible P-CH3 bond cleavage.
Mechanistic considerations for C-C bond reductive coupling at a cobalt(III) center
Xu, Hongwei,Bernskoetter, Wesley H.
, p. 14956 - 14959 (2011)
The diamagnetic cobalt(III) dimethyl complex, cis,mer-(PMe 3)3Co(CH3)2I, was found to promote selective C-C bond formation, affording ethane and triplet (PMe 3)3CoI. The mechanism of reductive elimination has been investigated by a series of kinetic and isotopic-labeling experiments. Ethane formation proceeds with a rate constant of 3.1(5) × 10-5 s -1 (50 °C) and activation parameters of ΔH a = 31.4(8) kcal/mol and ΔS a = 17(3) eu. Addition of free trimethylphosphine or coordinating solvent strongly inhibits reductive elimination, indicating reversible phosphine dissociation prior to C-C bond-coupling. EXSY NMR analysis established a rate constant of 9(2) s-1 for phosphine loss from cis,mer-(PMe3)3Co(CH3)2I. Radical trapping, crossover, and isotope effect experiments were consistent with a proposed mechanism for ethane extrusion where formation of an unobserved five-coordinate intermediate is followed by concerted C-C bond formation. An unusual intermolecular exchange of cobalt-methyl ligands was also observed by isotopic labeling.
A NMR method for the analysis of mixtures of alkanes with different deuterium substitutions
Loaiza, Alfonso,Borchardt, Dan,Zaera, Francisco
, p. 2481 - 2493 (1997)
13C NMR at 125.76 MHz with 1H and 2H decoupling, 2H NMR at 76.77 MHz with 1H decoupling, and 1H NMR at 500.14 MHz with 2H decoupling were employed as analytical tools to study the complex mixtures of deuterated ethanes resulting from the catalytic H-D exchange of normal ethane with gas-phase deuterium in the presence of a platinum foil. Reference samples consisting of 1:1 binary mixtures of pure normal ethane and ethane-dn (n = 1-6) were used to identify the peak positions in the 13C, 2H, and 1H NMR spectra due to each individual isotopomer, and the effect of isotopic substitution on the chemical shifts was determined in each case. While the NMR of all three nuclei worked well for the identification of the individual components of the 1:1 standard mixtures, both 1H and 2H NMR suffered from inadequate resolution when studying complex reaction mixtures because of the broadening of the lines due to 1H-1H (1H NMR) and 2H-2H (2H NMR) couplings. 13C NMR was therefore determined to be the method of choice for the quantitative analysis of the reaction mixtures. Using the 13C NMR results, a correlation that takes into account the primary and secondary isotope substitution effects on chemical shifts was deduced. This equation was used for the identification of the individual components of the mixtures, and integration of the individual observed resonances was then employed for quantification of their composition. This study shows that 13C NMR with 1H and 2H decoupling is a viable procedure for studying mixtures of deuterated ethanes. Furthermore, the additivity of the isotopic effects on chemical shifts and the transferability of the values obtained with ethane to other molecules makes this approach general for the analysis of other isotopomer mixtures.
Hydrogenation of Ethylene on Metal Electrodes. Part 5. Reduction of Light Ethylene on Pt in Deuteroperchloric Acid Solution and the Dual-pathway Mechanism
Fujikawa, Keikichi,Kita, Hideaki,Sato, Shinri
, p. 3055 - 3072 (1981)
Electroreduction of light ethylene on a platinum electrode was conducted in a heavy-water solution of deuteroperchloric acid.Deuterium-atom distributions in the product, ethane, support the previous conclusion that ethylene diffusion is rate-controlling at potentials less positive than ca. 100 mV, whereas the surface reaction is rate-controlling at more positive potentials where the Tafel line holds.The D-atom distribution in the latter potential region reveals double maxima at - and -ethanes.This distribution is explained by the dual-pathway mechanism which assumes two reaction rates for the step C2H4(a) + H(a) C2H5(a).The difference in the reaction rate will be attributed to the difference in the adsorption state of C2H4(a) but not of H(a), since only the weakly adsorbed hydrogen atoms are active in the hydrogenation.Reduction of light ethylene with D2 on platinum in deuteroperchloric acid solution gives the same results.A computer simulation based on the above mechanism can reproduce quantitatively not only the present distributions but also others given in the literature, even those observed for the gas-phase heterogeneous reduction.
Alkylperoxy and Alkyl Radicals. 1. Infrared Spectra of CH3O2 and CH3O4CH3 and the Ultraviolet Photolysis of CH3O2 in Argon + Oxygen Matrices
Ase, P.,Bock, W.,Snelson, A.
, p. 2099 - 2109 (1986)
Methyl radicals, generated by the pyrolysis of azomethane and/or methyl iodide, were allowed to interact with matrices of Ar + 10percent O2 and the products isolated.IR spectra were obtained for species containing the following isotopically labeled groups: CH3, 13CH3, CD3, 16O2, 18O2 and 16O(18)O.From these spectra, the methylperoxy radical and its dimer, dimethyltetroxide, were identified and vibrational assignments made.Irradiation of CH3O2 at ca. 254 nm resulted in its photodissociation.The nature of this process in the matrix is discussed.
Changes in ligand coordination mode induce bimetallic C-C coupling pathways
Blacquiere, Johanna M.,Boyle, Paul D.,Jackman, Kyle M. K.,Liang, Guangchao,Zimmerman, Paul M.
supporting information, p. 3977 - 3991 (2022/03/31)
Carbon-carbon coupling is one of the most powerful tools in the organic synthesis arsenal. Known methodologies primarily exploit monometallic Pd0/PdII catalytic mechanisms to give new C-C bonds. Bimetallic C-C coupling mechanisms that involve a PdI/PdII redox cycle, remain underexplored. Thus, a detailed mechnaistic understanding is imperative for the development of new bimetallic catalysts. Previously, a PdII-Me dimer (1) supported by L1, which has phosphine and 1-azaallyl donor groups, underwent reductive elimination to give ethane, a PdI dimer, a PdII monometallic complex, and Pd black. Herein, a comprehensive experimental and computational study of the reactivity of 1 is presented, which reveals that the versatile coordination chemistry of L1 promotes bimetallic C-C bond formation. The phosphine 1-azaallyl ligand adopts various bridging modes to maintain the bimetallic structure throughout the C-C bond forming mechanism, which involves intramolecular methyl transfer and 1,1-reductive elimination from one of the palladium atoms. The minor byproduct, methane, likely forms through a monometallic intermediate that is sensitive to solvent C-H activation. Overall, the capacity of L1 to adopt different coordination modes promotes the bimetallic C-C coupling channel through pathways that are unattainable with statically-coordinated ligands.
A Comparative Analysis of the CO-Reducing Activities of MoFe Proteins Containing Mo- and V-Nitrogenase Cofactors
Lee, Chi Chung,Tanifuji, Kazuki,Newcomb, Megan,Liedtke, Jasper,Hu, Yilin,Ribbe, Markus W.
, p. 649 - 653 (2018/04/16)
The Mo and V nitrogenases are structurally homologous yet catalytically distinct in their abilities to reduce CO to hydrocarbons. Here we report a comparative analysis of the CO-reducing activities of the Mo- and V-nitrogenase cofactors (i.e., the M and V clusters) upon insertion of the respective cofactor into the same, cofactor-deficient MoFe protein scaffold. Our data reveal a combined contribution from the protein environment and cofactor properties to the reactivity of nitrogenase toward CO, thus laying a foundation for further mechanistic investigation of the enzymatic CO reduction, while suggesting the potential of targeting both the protein scaffold and the cofactor species for nitrogenase-based applications in the future.
Hydrogen/Deuterium-Exchange Reactions of Methane with Aromatics and Cyclohexane Catalyzed by a Nanoscopic Aluminum Chlorofluoride
Calvo, Beatriz,Braun, Thomas,Kemnitz, Erhard
, p. 403 - 406 (2017/12/26)
H/D-exchange reactions between methane and deuterated solvents such as [D6]benzene and [D12]cyclohexane were heterogeneously catalyzed by nanoscopic aluminum chlorofluoride (ACF=AlClxF3?x, x≈0.05–0.3) under very mild conditions. 13C NMR spectroscopy experiments at labeled methane revealed the formation of all isotopologues. AlCl3, AlBr3, HS-AlF3, γ-Al2O3, and γ-Al2O3 preheated at 700 °C did not show any H/D-exchange reaction of methane or [D6]benzene. Mechanistically, electrophilic activation of methane was suggested at the ACF surface.
