Video Experimental Relacionado

Updated: Jul 19, 2026

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Published on: April 1, 2013

La activación a temperatura ambiente de las haloporfirinas-enediinas: contribuciones electrónicas a la

Mahendra Nath¹, John C Huffman, Jeffrey M Zaleski

¹Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.

Journal of the American Chemical Society

|September 18, 2003

Resumen

Este estudio sintetiza nuevas porfirinas de níquel (II) con sustitutos de haloetinile. Estos compuestos se someten a la ciclización de Bergman, dando lugar a estructuras complejas de porfirina, con activación a temperatura ambiente observada bajo condiciones específicas.

Área de la Ciencia:

Química orgánica es la química orgánica.
Ciencia de los materiales Ciencia de los materiales.
Coordinación Química de la Coordinación

Sus antecedentes:

Las tetrafenilporfirinas son macrociclos versátiles con aplicaciones en catálisis y ciencias de los materiales.
La funcionalización de las periferias de la porfirina permite ajustar las propiedades electrónicas y estructurales.
Los sustituyentes de etinyl ofrecen asas reactivas para futuras transformaciones químicas.

Objetivo del estudio:

Para sintetizar el nuevo níquel (II) 2,3-bis (haloetinile) 5,10,15,20-tetrafenilporfirinas.
Para investigar la ciclización de Bergman de estos nuevos derivados de la porfirina.
Explorar los factores que influyen en la reacción de ciclización, incluyendo la temperatura y los aditivos.

Principales métodos:

Síntesis del níquel (II) 2,3-diethynyl-5,10,15,20-tetraphenylporphyrin a través del acoplamiento cruzado y la desprotección.
Halogenación de los grupos etinyl utilizando N-bromo- o N-iodosuccinimida.
La termólisis y las reacciones a temperatura ambiente en varios disolventes con o sin aditivos como el 1,4-ciclohexadieno (CHD) y la 2,3-dicloro-5,6-diciano-1,4-benzoquinona (DDQ).

Principales resultados:

Se ha logrado la síntesis de las tetrafenilporfirinas de níquel (II) 2,3-bis (bromoetinile) - (2a) y bis (iodoetinile) - (2b).
Las estructuras cristalinas de rayos X revelan una no-planaridad significativa en la columna vertebral de la porfirina debido a la coordinación de Ni (II).
La termólisis de 2a y 2b produce productos ciclizados de Bergman (3, 4, 5) a través de reacciones de adición o sustitución diradical.
Se logra una ciclización de la temperatura ambiente de 2a, acelerada significativamente por el DDQ, lo que indica una fácil formación de productos Bergman.

Conclusiones:

Las porfirinas de níquel (II) con sustitutos de haloetinile pueden sintetizarse y someterse a la ciclización de Bergman.
La presencia de grupos de haloetinile que retiran electrones reduce la barrera de activación para la ciclización de Bergman.
La ciclización de la temperatura ambiente es factible, especialmente con la ayuda de oxidantes como el DDQ, abriendo nuevas vías sintéticas.

Más Videos Relacionados

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core

Published on: October 24, 2017

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Published on: December 27, 2018

Videos de Conceptos Relacionados

Thermal and Photochemical Electrocyclic Reactions: Overview

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

Photochemical Electrocyclic Reactions: Stereochemistry

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

ortho–para-Directing Activators: –CH3, –OH, –&NoBreak;NH2, –OCH3

ortho–para-Directing Activators: –CH₃, –OH, –⁠NH₂, –OCH₃

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...

ortho–para-Directing Deactivators: Halogens

ortho–para-Directing Deactivators: Halogens

Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Cycloaddition Reactions: MO Requirements for Photochemical Activation

Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.