594-11-6Relevant articles and documents
Application of aerosol techniques to study the catalytic formation of methane on gasborne nickel nanoparticles
Weber,Seipenbusch,Kasper
, p. 8958 - 8963 (2001)
A well known reaction, the so-called methanation reaction over a Ni catalyst, i.e., the formation of methane from CO and hydrogen, was studied to demonstrate the possibilities of the aerosol technique. Reaction order and activation energy conformed to generally accepted values from supported Ni catalysts. The turnover rate (TOR) decreased strongly during the first 10 sec as the reaction proceeded toward a steady value. The decrease correlated with a buildup of about 0.3 monolayer equivalents of carbon on the particle surface measured by TGA and a decline in particle photoelectric activity found via measurement by aerosol photoemission spectroscopy. Order-of-magnitude changes were induced in TOR via defined changes in particle morphology induced by aerosol restructuring techniques preceeding exposure to the catalytic reaction. Aerosol catalysis has potential to develop new catalysts and could be an avenue for studying the putative relationship between combustion aerosols and the formation of dioxin.
Evidence for Retention of the Cyclic C3H5 Structure during Positive-ion Processes in the Gas Phase
Colosimo, Marcello,Bucci, Roberto
, p. 659 - 661 (1981)
The decomposition of gaseous cyclopropylmethylbromonium ions has yielded the cyclic hydrocarbons cyclopropane and methylcyclopropane, and methyl bromide.
Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage
Fast, Caleb D.,Schley, Nathan D.
supporting information, p. 3291 - 3297 (2021/10/12)
A catalytic, light-promoted hydrosilylative cleavage reaction of alkyl ethers is reported. Initial studies are consistent with a mechanism involving heterolytic silane activation followed by delivery of a photohydride equivalent to a silyloxonium ion generated in situ. The catalyst resting state is a mixture of Cp*Ir(ppy)H (ppy = 2-phenylpyridine-κC,N) and a related hydride-bridged dimer. Trends in selectivity in substrate reduction are consistent with nonradical mechanisms for C-O bond scission. Irradiation of Cp*Ir(ppy)H with blue light is found to increase the rate of hydride delivery to an oxonium ion in a stoichiometric test. A comparable rate enhancement is found in carbonyl hydrosilylation catalysis, which operates through a related mechanism also involving Cp*Ir(ppy)H as the resting state.
Experimental evidence for heavy-atom tunneling in the ring-opening of cyclopropylcarbinyl radical from intramolecular 12C/13C kinetic isotope effects
Gonzalez-James, Ollie M.,Zhang, Xue,Datta, Ayan,Hrovat, David A.,Borden, Weston Thatcher,Singleton, Daniel A.
supporting information; experimental part, p. 12548 - 12549 (2010/11/05)
The intramolecular 13C kinetic isotope effects for the ring-opening of cyclopropylcarbinyl radical were determined over a broad temperature range. The observed isotope effects are unprecedentedly large, ranging from 1.062 at 80 °C to 1.163 at -100 °C. Semiclassical calculations employing canonical variational transition-state theory drastically underpredict the observed isotope effects, but the predicted isotope effects including tunneling by a small-curvature tunneling model match well with experiment. These results and a curvature in the Arrhenius plot of the isotope effects support the recently predicted importance of heavy-atom tunneling in cyclopropylcarbinyl ring-opening.
Homolytic C-S bond scission in the desulfurization of aromatic and aliphatic thiols mediated by a Mo/Co/S cluster: Mechanistic aspects relevant HDS catalysis
Curtis, M. David,Druker, Scott H.
, p. 1027 - 1036 (2007/10/03)
The kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined. These reactions form cluster 2 and the arene or alkane corresponding to the thiol: Cp'2Mo2Co2S3(CO)4 (1) + RSH → Cp'2Mo2Co2S4(CO)2 (2) + RH + 2CO. These reactions are first order in thiol and first order in cluster 1 with appreciable negative entropies of activation. These data suggest that the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster. The more nucleophilic thiolate anions react with 1 at -40°C to form an adduct in which the thiolate anion is bound η1 to the Co atom. At -25°C, the initial adduct rearranges to a fluxional μ2, η1-bound thiolate. The fluxional process is proposed to involve a concerted 'walking' of the thiolate and a μ2-bound sulfide ligand on the surface of the cluster. Near 35°C, the thiolate-cluster adduct undergoes C-S bond homolysis to give the paramagnetic anion of cluster 1 and the phenyl or alkyl radical. The radical nature of the C-S bond cleavage was confirmed by the desulfurization of the radical clock reagents, cyclopropylmethanethiol and -thiolate anion, that form the cyclopropylmethyl radical which rearranged to the butenyl radical. The possible similarity in the C-S bond cleavage mechanism in these desulfurization reactions to those occurring in hydrodesulfurization (HDS) over Co/Mo/S catalysts is discussed.
Ion and radical rearrangements as a probe of the mechanism of a surface reaction : The desulfurization of cyclopropylmethanethiol and 3-butene-1-thiol on Mo(110)
Wiegand,Napier,Friend,Uvdal
, p. 2962 - 2968 (2007/10/03)
Rearrangement reactions were used to probe the transient intermediates in thiol desulfurization induced by Mo(110) by studying cyclopropylmethanethiol and 3-butene-1-thiol. Thiolate intermediates were identified in both cases using vibrational spectroscopy, which indicates facile S-H bond scission on Mo(110). Heterolytic C-S bond scission, leading to a cationic intermediate, is excluded based on the lack of rearrangement products in the reactions of 3-butene-1-thiolate and the absence of cyclobutane or cyclobutene in the reaction of cyclopropylmethyl thiolate on Mo(110). Hydrogenolysis without rearrangement is the primary pathway for both thiols investigated. The lack of rearrangement in the 3-butene-1-thiolate indicates that C-S bond scission and C-H bond formation occur nearly simultaneously. Evidence for the radical pathway is obtained from the production of 1,3-butadiene formed via the rearrangement of cyclopropylmethyl group following C-S bond scission in the cyclopropylmethyl thiolate and by related studies of cyclopropylmethyl bromide. The investigation of the cyclopropylmethyl bromide also demonstrates that trapping of the cyclopropylmethyl radical is favored over selective β-dehydrogenation. This is the first study in which radical rearrangements have been used to obtain detailed information about the nature of extremely short-lived reactions in a surface process.
Titanium Catalyzed Reduction of Aromatic Halides by Sodium Borohydride
Liu, Yumin,Schwartz, Jeffrey
, p. 4471 - 4482 (2007/10/02)
The reduction of aryl halides by sodium borohydride is catalyzed by titanium complexes; di(cyclopentadienyl)titanium dichloride (titanocence dichloride) is highly effective.The reaction scope and mechanism are solvent dependent.In dimethylformamide (DMF), an adduct of DMF and sodium borohydride is formed which reduces simple aryl halides by a non-radical, likely nucleophilic route.Dimethylamino- substituted products are formed, as are simple dechlorinated species.In dimethylacetamide or in ethers, a radical-based reaction involving activated titanocene borohydride takes place, and only dechlorinated products result.
The Mechanism of Titanium Complex-Catalyzed Reduction of Aryl Halides by Sodium Borohydride Is Strongly Solvent Dependent
Liu, Yumin,Schwartz, Jeffrey
, p. 940 - 942 (2007/10/02)
The titanium complex-catalyzed reduction of aryl halides by sodium borohydride in dimethylacetamide (DMA) or ethers proceeds by electron transfer from a reduced titanium species, yielding an intermediate aryl radical.
Picosecond radical kinetics. Rate constants for reaction of benzeneselenol with primary alkyl radicals and calibration of the 6-cyano-5-hexenyl radical cyclization
Newcomb, Martin,Varick, Thomas R.,Ha, Chau,Manek, M. Beata,Yue, Xu
, p. 8158 - 8163 (2007/10/02)
The cyclopropylcarbinyl radical ring opening was used as a radical clock to determine rate constants for benzeneselenol trapping in THF and in toluene. Hydrogen atom transfer trapping from PhSeH appeared to be partially diffusion controlled. An operational Arrhenius function for trapping in THF is log (kT·M s) = 11.03 - 2.21/2.3RT. The recommended function for PhSeH trapping in other low-viscosity organic solvents is log (kT·M s) = 10.87 - 2.10/2.3RT. The rate constant for trapping at 25°C is 2.1 × 109 M-1 s-1. The kinetic values are expected to apply for PhSeH trapping of simple primary alkyl radicals. As a check on this assumption, cyclization of the 6-cyano-5-hexenyl radical (9), produced from the corresponding PTOC ester radical precursor, was calibrated with PhSH and PhSeH trapping. The two trapping agents gave essentially equivalent results. The cyclizations of both (E)- and (Z)-9 are described by log (kr·s) = 11.0 - 3.8/2.3RT. This fast rearrangement (kr = 1.6 × 108 s-1 at 25°C) could prove to be useful as a radical clock for timing fast second-order processes.
Synthesis, Structure, and Reactions of Stable Titanacyclopentanes
Mashima, Kazushi,Sakai, Nozomu,Takaya, Hidemasa
, p. 2475 - 2483 (2007/10/02)
Titanacyclic compounds of the formula Cp*2Ti(CH2CH2C(CH2CHR)CH2) (5a; R=H and 5b; R=C6H5, Cp*=pentamethylcyclopentadienyl), the first stable titanacyclopentanes, have been prepared by the reaction of bis(pentamethylcyclopentadienyl)titanium-ethylene complex (3) with methylenecyclopropanes (4), and their structures were determined based on both spectroscopic data and X-ray crystallography.Complex 5b crystallized in space group P21/a (Z=4) with cell constants, a=21.832(3), b=8.580(1), c=14.759(2) Angstroem, β=96.81(1) deg, U=2744.9(6) Angstroem3 (4261 reflections, R=0.053).The reaction of 5 with carbon monoxide afforded spiroheptan-5-ones in 98percent yield.The thermal decomposition of 5 has been investigated, and possible mechanisms of the reactions have been proposed based on deuterium-labeled experiments.A novel formal reductive elimination of organic ligands giving 1-phenylspirohexane has been observed in the thermolysis of 5b.A structure-reactivity relationship has been discussed.
