Intramolecular effects in the cycloaddition of three ethylenes vs. the Diels–Alder reaction

Ioffe, A.; Shaik, Sason

doi:10.1039/p29920002101

Cited by 36 publications

(35 citation statements)

References 38 publications

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“…This can be exemplified for the archetypical case of acetylene, where the activation energy of the concerted cyclisation mechanism towards benzene was estimated to be around 250 kJ mol À1 . 79 Nevertheless, such reactions are of great synthetic significance because they permit access to functional cyclic aromatic systems.…”

Section: B) Mesoporous Graphitic Carbon Nitride As a Catalyst For Thementioning

confidence: 99%

Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

et al. 2008

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Graphitic carbon nitride, g-C 3 N 4 , can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C 3 N 4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C 3 N 4 species, based on tri-s-triazine (C 6 N 7 ) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.

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Section: B) Mesoporous Graphitic Carbon Nitride As a Catalyst For Thementioning

confidence: 99%

Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

et al. 2008

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“…In this case, it is found that G = 173 kcal mol À1 because of the much lower E ST value of 1,3-butadiene. [32] The parameter f reflects the fraction of G that is responsible for the height of the crossing energy DE c . If we assume a value of f % 0.3 for thermally allowed pericyclic reactions, [32] we obtain DE c % 103.7 kcal mol À1 and therefore B % 58.6 kcal mol…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

Double Group Transfer Reactions: Role of Activation Strain and Aromaticity in Reaction Barriers

Fernández

Bickelhaupt

Cossío

2009

Chemistry A European J

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Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in-plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high-energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile DeltaE(zeta) and the height of the overall reaction barrier DeltaE( not equal)=DeltaE(zeta=zeta(TS)) is interpreted in terms of the strain energy DeltaE(strain)(zeta) associated with deforming the reactants along the reaction coordinate zeta plus the interaction energy DeltaE(int)(zeta) between these deformed reactants: DeltaE(zeta)=DeltaE(strain)(zeta)+DeltaE(int)(zeta). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states.

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“…[14,[22][23][24][25] Finally, we can briefly mention here that the uncatalysed thermal cyclotrimerisation is disfavoured entropically and has a high activation barrier. [26,27] To the best of our knowledge, a theoretical study of the reaction mechanism of the transition-metal-catalysed [2+2+2] cyclotrimerisation reaction in a macrocyclic triyne has yet to be performed. This [2+2+2] reaction should be favoured over cyclotrimerisation reactions involving free acetyl-A C H T U N G T R E N N U N G ene molecules for entropic reasons.…”

mentioning

confidence: 99%

Rhodium(I)‐Catalysed Intramolecular [2+2+2] Cyclotrimerisations of 15‐, 20‐ and 25‐Membered Azamacrocycles: Experimental and Theoretical Mechanistic Studies

Dachs¹,

Torrent²,

Roglans³

et al. 2009

Chemistry A European J

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A new series of 20- and 25-membered polyacetylenic azamacrocycles have been satisfactorily prepared and completely characterised by spectroscopic methods. Various [2+2+2] cyclotrimerisation processes catalysed by the Wilkinson's catalyst, [RhCl(PPh(3))(3)], were tested in the above-mentioned macrocycles. The 25-membered azamacrocycle (like the previously synthesised 15-membered azamacrocyle) led to the expected cyclotrimerised compound in contrast to the 20-membered macrocycle, which is characterised by its lack of reactivity. The difference in reactivity of the 15-, 20- and 25-membered macrocycles has been rationalised through density functional theory calculations.

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Intramolecular effects in the cycloaddition of three ethylenes vs. the Diels–Alder reaction

Cited by 36 publications

References 38 publications

Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

Double Group Transfer Reactions: Role of Activation Strain and Aromaticity in Reaction Barriers

Rhodium(I)‐Catalysed Intramolecular [2+2+2] Cyclotrimerisations of 15‐, 20‐ and 25‐Membered Azamacrocycles: Experimental and Theoretical Mechanistic Studies

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