The addition of alkynes to a tetrasilyldisilene — Evidence for a biradical intermediate

2005 ◽  
Vol 83 (9) ◽  
pp. 1568-1576 ◽  
Author(s):  
Stephen E Gottschling ◽  
Michael C Jennings ◽  
Kim M Baines
Keyword(s):  
Reaction Mechanism ◽  
Key Words ◽  
Cycloaddition Reaction ◽  
Major Product ◽  
Convincing Evidence ◽  
Mechanistic Probe

The addition of two newly developed mechanistic probes, (trans,trans-2-methoxy-3-phenylcyclopropyl)ethyne (1) and (trans,trans-2-methoxy-1-methyl-3-phenylcyclopropyl)ethyne (2), to tetrakis(tert-butyldimethylsilyl)disilene (3) has been investigated. The addition of 1 to 3 gave 1-[2-(cis-2-methoxy-3-phenylcyclopropylidene)vinyl]-1,1,2,2-tetrakis(tert-butyldimethylsilyl)disilane (5) as the major product; whereas addition of alkyne 2 to the disilene gave three stereoisomers of 1,1,2,2-tetrakis(tert-butyldimethylsilyl)-6-methoxy-5-methyl-7-phenyl-1,2-disilacyclohepta-3,4-diene (7–9) and 1,1,2,2- tetrakis(tert-butyldimethylsilyl)-3-(trans,trans-2-methoxy-1-methyl-3-phenylcyclopropyl)-1,2-disilacy-clobut-3-ene (10) as the major products. The formation of cycloheptaallenes 7–9 provides convincing evidence that the addition of alkynes to tetrasilyldisilenes involves the formation of a biradical intermediate. Key words: disilene, alkyne, cycloaddition, reaction mechanism, mechanistic probe.

A mechanistic study of the addition of alkynes to Brook silenes

2009 ◽  
Vol 87 (1) ◽  
pp. 307-313 ◽  
Author(s):  
Kaarina K Milnes ◽  
Kim M Baines
Keyword(s):  
Reaction Mechanism ◽  
Cycloaddition Reaction ◽  
Convincing Evidence ◽  
Membered Ring ◽  
Mechanistic Study ◽  
Mechanistic Probe

The addition of the alkyne-containing mechanistic probes (trans-2-phenylcyclopropyl)ethyne, (trans,trans-2-methoxy-3-phenylcyclopropyl)ethyne, and (trans,trans-2-methoxy-1-methyl-3-phenylcyclopropyl)ethyne (1a–1c) to a Brook silene 2-(1-adamantyl)-2-trimethylsiloxy-1,1-bis(trimethylsilyl)-1-silene (14) was examined. When alkyne 1a was added to the silene, an ene adduct was observed; however, addition of alkyne 1c to 14 gave a mixture of silacyclo butenes and silacycloheptenes. The regiochemistry of the phenyl and methoxy substituents on the seven-membered ring of the silacycloheptenes provides convincing evidence for the formation of a biradical intermediate along the reaction pathway.Key words: Brook silene, alkyne, cycloaddition, reaction mechanism, mechanistic probe.

Insights into the cycloaddition reaction mechanism between ketenimine and unsaturated hydrocarbon: A theoretical study

2016 ◽  
Vol 90 (5) ◽  
pp. 1027-1033 ◽  
Author(s):  
Wenxing He ◽  
Hong Zhang ◽  
Nana Wang ◽  
Xiaojun Tan ◽  
Weihua Wang ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Theoretical Study ◽  
Cycloaddition Reaction ◽  
Unsaturated Hydrocarbon

The Laser-Induced Nitrations of Several Hydrocarbons

1989 ◽  
Vol 43 (4) ◽  
pp. 674-681 ◽  
Author(s):  
A. E. Stanley ◽  
S. E. Godbey
Keyword(s):  
Reaction Mechanism ◽  
Nitrogen Dioxide ◽  
Chain Length ◽  
Continuous Wave ◽  
Infrared Laser ◽  
Major Product ◽  
Short Chain ◽  
Analogous Reaction ◽  
Thermal Reactions

The Army uses nitrated compounds as explosives and propellants. The ability to selectively nitrate materials is a much-needed process. Laser-induced chemistry possesses the potential to drive some reactions in an efficient and selective manner. Laser-induced chemistry may be useful in driving nitration reactions toward specific products. Reported herein are the results of several successful attempts to laser-induce the reaction of nitrogen dioxide with hydrocarbons of 3, 4, and 5 carbons. Specifically, the tunable continuous wave (cw) infrared laser was used to drive the reaction between nitrogen dioxide, NO2, and propane, n-butane, isobutane, and n-pentane. The major products of the reactions were secondary (tertiary in the isobutane reaction) nitrohydrocarbons, of the same chain length as the reacting hydrocarbon. Some short-chain nitrated compounds were also identified. The yield of 2-nitrobutane observed in the nitration of butane is ∼20% on the basis of the depletion of NO2. The propane reacted with NO2 to produce mostly 2-nitropropane with a smaller yield of 5–9%. The analogous reaction of pentane produced ∼9% of the major product, which is believed to be 2-nitropentane. The isobutane nitration resulted in approximately a 10% yield of 2-methyl-2-nitropropane. The results of these laser-induced reactions are contrasted to the corresponding thermal reactions. The reaction mechanism is also discussed for these two processes.

Theoretical study on the cycloaddition reaction mechanism between ketenimine and acetonitrile

2016 ◽  
Vol 15 (3) ◽  
pp. 221-230 ◽  
Author(s):  
Wenxing He ◽  
Weihua Wang ◽  
Xiaojun Tan ◽  
Ping Li
Keyword(s):  
Reaction Mechanism ◽  
Theoretical Study ◽  
Cycloaddition Reaction

scholarly journals Investigation of the reaction mechanism of [4 + 2] cyclization of 2,3 dimethylbuta-1,3-diene to methylacrylate using the Michaelis-Menten equation

2018 ◽  
Vol 6 (1) ◽  
pp. 74-81
Author(s):  
Irina Kostiv
Keyword(s):  
Reaction Mechanism ◽  
Molecular Complex ◽  
Rate Constants ◽  
Van Der Waals ◽  
Cycloaddition Reaction ◽  
Effective Rate ◽  
Second Order ◽  
Van Der Waals Interaction ◽  
Reaction Proceeds ◽  
Limiting Stage

The cycloaddition reaction between 2,3‑dimethylbuta-1,3-diene and methylacrylate proceeds by the second order kinetics. The rate constants increase with the increase in the excess of one of the reactants. The change in the effective rate constants is described by the Michaelis–Menten equation indicating that the reaction proceeds through the initial equilibrium stage of formation of a molecular complex stabilized by van der Waals interaction which then transforms into the product. The limiting stage of the reaction is established and its mechanism is suggested.

Hydrosilylation of alkenes and ketones catalyzed by nickel(II) indenyl complexes

2003 ◽  
Vol 81 (11) ◽  
pp. 1299-1306 ◽  
Author(s):  
Frédéric-Georges Fontaine ◽  
René-Viet Nguyen ◽  
Davit Zargarian
Keyword(s):  
Reaction Mechanism ◽  
Key Words ◽  
Room Temperature ◽  
Active Species ◽  
The Other ◽  
Silyl Ethers ◽  
Cationic Species ◽  
Catalytically Active ◽  
High Yields ◽  
Indenyl Complexes

Abstraction of Cl– from the complexes (indenyl)Ni(PPh3)Cl generates cationic species that are effective precatalysts for the hydrosilylation of some olefins and ketones. For instance, the mixture of (1-Me-indenyl)Ni(PPh3)Cl and NaBPh4 (or methylaluminoxane) reacts at room temperature with ca. 100 equiv. each of PhSiH3 and styrene to produce [1-phenyl-1-ethyl](phenyl)silane, PhCH(CH3)(SiPhH2), in 50%–80% yield. The same system can also catalyze the hydrosilylation of 1-hexene and norbornene, but the products arising from these substrates consist of mixtures of regio- and stereoisomers. On the other hand, ketone hydrosilylation is regiospecific, giving the corresponding silyl ethers in high yields. A number of experimental observations have indicated that the initially generated Ni-based cation is not the catalytically active species. Indeed, the cationic initiators may be replaced by LiAlH4 or AlMe3, which generate the corresponding Ni-H or Ni-Me derivatives, respectively. Moreover, the observed regioselectivity for the addition of PhSiH3 to styrene (i.e., predominant addition of the silyl fragment to the α-C) is opposite of what would be expected if the reaction mechanism involved carbocationic intermediates. A new mechanism is proposed in which the active species is a Ni-H species originating from the transfer of H– from PhSiH3 to the initially generated Ni cation. Key words: hydrosilylation, nickel indenyl complexes, cationic complexes, hydride intermediates.

scholarly journals Full atomistic reaction mechanism with kinetics for CO reduction on Cu(100) from ab initio molecular dynamics free-energy calculations at 298 K

2017 ◽  
Vol 114 (8) ◽  
pp. 1795-1800 ◽  
Author(s):  
Tao Cheng ◽  
Hai Xiao ◽  
William A. Goddard
Keyword(s):  
Free Energy ◽  
Reaction Mechanism ◽  
Ab Initio ◽  
Rational Design ◽  
Major Product ◽  
Free Energy Calculations ◽  
Ab Initio Molecular Dynamics ◽  
Applied Potential ◽  
Hydrogen Electrode ◽  
Energy Calculations

A critical step toward the rational design of new catalysts that achieve selective and efficient reduction of CO2to specific hydrocarbons and oxygenates is to determine the detailed reaction mechanism including kinetics and product selectivity as a function of pH and applied potential for known systems. To accomplish this, we apply ab initio molecular metadynamics simulations (AIMμD) for the water/Cu(100) system with five layers of the explicit solvent under a potential of −0.59 V [reversible hydrogen electrode (RHE)] at pH 7 and compare with experiment. From these free-energy calculations, we determined the kinetics and pathways for major products (ethylene and methane) and minor products (ethanol, glyoxal, glycolaldehyde, ethylene glycol, acetaldehyde, ethane, and methanol). For an applied potential (U) greater than −0.6 V (RHE) ethylene, the major product, is produced via the Eley–Rideal (ER) mechanism using H2O +e–. The rate-determining step (RDS) is C–C coupling of two CO, with ΔG‡= 0.69 eV. For an applied potential less than −0.60 V (RHE), the rate of ethylene formation decreases, mainly due to the loss of CO surface sites, which are replaced by H*. The reappearance of C2H4along with CH4atUless than −0.85 V arises from *CHO formation produced via an ER process of H* with nonadsorbed CO (a unique result). This *CHO is the common intermediate for the formation of both CH4and C2H4. These results suggest that, to obtain hydrocarbon products selectively and efficiency at pH 7, we need to increase the CO concentration by changing the solvent or alloying the surface.

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