Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance
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Abstract:
A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.Keywords:
Alkene
Reactivity
Hexane
Space velocity
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The first Ni-catalysed alkene isomerization of allylamides for the synthesis of enamides was demonstrated. Various substituted N-allylamides were found to be suitable substrates for this isomerization. Isotopic labelling experiments showed that it is an intramolecular hydrogen transfer process.
Alkene
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The isomerization (chain-walking) reaction of terminal to internal alkenes is catalyzed by part-per-million amounts of practically any Ru source when the reaction is carried out with a neat terminal alkene. Here, we provide evidence that the soluble starting Ru sources evolve to catalytically active peralkene Ru(II) species under reaction conditions. These species may also explain the isomerization products found during other Ru-catalyzed alkene processes, i.e., alkene metathesis reactions. A Finke-Watzky mechanism for catalyst formation is consistent with the evidence obtained.
Alkene
Salt metathesis reaction
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Isomerization of saturated hydrocarbons includes skeletal rearrangements and cis-trans isomerization of substituted cycloalkanes. Different catalysts bring about different types of isomerization of hydrocarbons. Acids are the best known and most important catalysts inducing isomerization through a carbocationic process. Bronsted and Lewis acids, acidic solids, and superacids are used in different applications. Significant efforts have been made about the fabrication, characterization, and the use of bifunctional catalysts bearing both acidic and metallic sites in isomerization. Metals are able to induce hydrogenation/dehydrogenation, whereas acid sites are involved in skeletal isomerization. Besides skeletal rearrangements, alkenes may undergo double-bond migration and cis-trans isomerization. Double-bond migration, cis-trans isomerization, and skeletal isomerization are the characteristic isomerization transformations of alkenes in the presence of acidic catalysts. Double-bond migration and cis-trans isomerization are facile transformations that can be induced under mild conditions (relatively mild acids and low temperature).
Brønsted–Lowry acid–base theory
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Interplay of STM imaging and DFT calculations demonstrates the isomerization of an alkene molecule on Cu(110) under ultrahigh vacuum conditions. We show that the on-surfacecis –trans isomerization could efficiently occur well below room temperature, in which the surface is speculated to play a key role in assisting this isomerization process.
Alkene
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Abstract Alkene isomerization and hydrogenation both using H 2 and sacrificial hydrogen donors are important reactions in synthetic chemistry. These reactions are normally catalyzed by second‐ or third‐row transition metals, but there has been significant recent interest in the development of first‐row systems. The different mechanisms for both alkene isomerization and hydrogenation are discussed along with strategies for catalyst modification to improve selectivity.
Alkene
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We report a single additive-responsive chromium-catalyzed system for selectively producing either of two different internal alkene isomers. The chromium catalyst, in the presence of HBpin/LiOtBu, enables the isomerization of alkenes over multiple carbon atoms to give the most thermodynamically stable isomers. The same catalyst allows for the selective isomerization of terminal alkenes over one carbon atom without an additive, exhibiting efficient and controllable alkene transposition selectivity.
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Efficient synthesis of medium-sized cyclic molecules containing an (E)-alkene was performed via the highly (E)-selective photochemical isomerization of the (Z)-isomer, facilitated by AgNO3-impregnated silica gel. Efficient synthesis of medium-sized cyclic molecules containing an (E)-alkene were accomplished by highly (E)-selective photochemical isomerization of the (Z)-isomer facilitated by presence of AgNO3-impregnated silica gel.
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Contrary to the hitherto accepted concept that every olefins undergo mutual isomerization between their cis-and trans-isomers, olefins substituted by anthracenyl and other aromatic polycyclic groups undergo only one-way isomerization from their cis-to trans-isomers, and the reverse isomerization from their trans-tocis-isomers never occurs. The mechanism for the one-way isomerization and the features to distinguish one-way or two-way isomerization is discussed to get whole view of the isomerization of olefins.
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