1632-99-1Relevant articles and documents
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.
Photochemical and thermal cobalt--carbon bond cleavage in alkylcobalamins and related organometallic compounds. A comparative stdy.
Schrauzer,Sibert,Windgassen
, p. 6681 - 6688 (1968)
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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.
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.
Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes
Rudenko, Andrey E.,Clayman, Naomi E.,Walker, Katherine L.,Maclaren, Jana K.,Zimmerman, Paul M.,Waymouth, Robert M.
supporting information, p. 11408 - 11415 (2018/09/12)
Reductive elimination (RE) is a critical step in many catalytic processes. The reductive elimination of unsaturated groups (aryl, vinyl and ethynyl) from Pd(II) species is considerably faster than RE of saturated alkyl groups. Pd(II) dimethyl complexes ligated by chelating diimine ligands are stable toward RE unless subjected to a thermal or redox stimulus. Herein, we report the spontaneous RE of ethane from (azpy)PdMe2 complexes and the unique role of the redox-active azopyridine (azpy) ligands in facilitating this reaction. The (azpy)PdMe2 complexes are air- and moisture-stable in the solid form, but they readily produce ethane upon dissolution in polar solvents at temperatures from 10 °C to room temperature without the need for an external oxidant or elevated temperatures. Experimental and computational studies indicate that a bimolecular methyl transfer precedes the reductive elimination step, where both steps are facilitated by the redox-active azopyridine ligand.
Bimetallic C-C Bond-Forming Reductive Elimination from Nickel
Xu, Hongwei,Diccianni, Justin B.,Katigbak, Joseph,Hu, Chunhua,Zhang, Yingkai,Diao, Tianning
supporting information, p. 4779 - 4786 (2016/05/09)
Ni-catalyzed cross-coupling reactions have found important applications in organic synthesis. The fundamental characterization of the key steps in cross-coupling reactions, including C-C bond-forming reductive elimination, represents a significant challenge. Bimolecular pathways were invoked in early proposals, but the experimental evidence was limited. We present the preparation of well-defined (pyridine-pyrrolyl)Ni monomethyl and monophenyl complexes that allow the direct observation of bimolecular reductive elimination to generate ethane and biphenyl, respectively. The sp3-sp3 and sp2-sp2 couplings proceed via two distinct pathways. Oxidants promote the fast formation of Ni(III) from (pyridine-pyrrolyl)Ni-methyl, which dimerizes to afford a bimetallic Ni(III) intermediate. Our data are most consistent with the subsequent methyl coupling from the bimetallic Ni(III) to generate ethane as the rate-determining step. In contrast, the formation of biphenyl is facilitated by the coordination of a bidentate donor ligand.
