Name: controlled photoredox ring-opening polymerization of o-carboxyanhydrides mediated by ni/zn complexes
Uploaded: 2017-11-21T15:00:00.000+00:00
Duration: 5 min 48 s
Description: Watch this Scientific Journal Video about Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes at JoVE.com

Este trabajo fue apoyado por la puesta en marcha fondos de Virginia Polytechnic Institute y State University. Q.F. reconoce apoyo de la Fundación Nacional de Ciencias naturales de China (21504047), Fundación de Ciencias naturales de la provincia de Jiangsu (BK20150834), Universidad de Nanjing de correos y telecomunicaciones científico Fundación NUPTSF (NY214179).

PRECAUCIÓN: Consulte los materiales pertinentes hojas de seguridad (MSDS) antes de su uso. Muchos productos químicos utilizados en la síntesis son muy tóxicos y cancerígenos. Utilice todas las prácticas de seguridad apropiadas cuando se realiza la reacción, incluyendo el uso de controles de ingeniería (campana y guantera) y equipo de protección personal (gafas, guantes, bata, pantalones largos, zapatos cerrados, luz azul bloqueo de seguridad gafas). Siguientes procedimientos incluyen técnicas de manejo de aire estándar en una caja de guantes. Todas las soluciones se transfieren con pipeta.
1. preparación del iniciador y catalizador
Nota: Todo el proceso se lleva a cabo en una guantera con una trampa de frío. Todos los productos químicos secos o purificados antes de pasar a la caja. 13 todos los frascos y cristalería son secados y calentados en el horno antes de pasar a la caja.
<ol><li>
Preparación de (bpy)Ni(COD) solución Nota: (bpy)Ni(COD) debe estar recién preparada en situ. Debe ser almacenado en el congelador (-35 ° C) de la caja de guante y utilizar dentro de una semana. Todas las soluciones de iniciador y otros catalizadores pueden guardarse en el congelador de la caja de guante más de 1 mes.<ol>
<li>Pesar Ni(COD)2 (3,5 mg, 12.7 μmol, 1,0 eq) en un vial de centelleo de 7 mL.</li>
		<li>Peso 2, 2 '-bipyridine (5,9 mg, 37.8 μmol) en un vial de centelleo de 7 mL.</li>
		<li>Disolver los 2, 2 '-bipyridine en 1 mL de tetrahidrofurano anhidro (THF).</li>
		<li>Añadir resultante 2, 2 '-bipyridine solución (337 μL) en el frasco que contiene Ni(COD)2.</li>
		<li>Diluir la mezcla en 1 mL de THF anhidro.</li>
		<li>Tapa el frasco y coloque la mezcla de reacción a temperatura ambiente durante 2 h. Nota: Ni(COD)2 no es soluble en THF, mientras que (bpy)Ni(COD) es soluble en THF. No debe haber ninguna precipitación en la solución púrpura después de 2 h.</li>
		<li>Tienda (bpy)Ni(COD) en el congelador de-35 ° C.</li>
	</ol>
</li>
	<li>
Preparación de solución de Zn(HMDS)2
	<ol>
<li>Añadir Zn(HMDS)2 (3,3 mg, 4 μL, 8.5 μmol) a un vial de centelleo de 7 mL.</li>
		<li>Zn(HMDS)2 en 1 mL de THF anhidro se disuelven.</li>
		<li>Almacene la solución de2 Zn(HMDS) en el congelador de-35 ° C.</li>
	</ol>
</li>
	<li>
Preparación de solución BnOH
	<ol>
<li>Añadir BnOH (4,0 mg, 4 μL, 37.0 μmol) a un vial de centelleo de 7 mL.</li>
		<li>BnOH en 4 mL de THF anhidro se disuelven.</li>
		<li>Almacenar la solución BnOH en el congelador de-35 ° C.</li>
	</ol>
</li>
	<li>
Preparación de la solución de Ir-1
	<ol>
<li>Apagar la luz de la guantera. PRECAUCIÓN: Es necesario apagar la luz de la guantera para evitar la desactivación de Ir-1 antes de la polimerización.</li>
		<li>Añadir Ir-1 (2,9 mg, 2.6 μmol) en un vial de centelleo de 7 mL.</li>
		<li>El Ir-1 en 3 mL de THF anhidro se disuelven.</li>
		<li>Almacenar la solución de Ir-1 en el congelador de-35 ° C.</li>
	</ol>
</li>
</ol>2. Photoredox anillo-abertura polimerización de l-1
Nota: Todo el proceso se lleva a cabo en una guantera con una trampa de frío. Todos los monómeros OCA son recristalizados en la guantera antes de su uso. 13 aquí nos dan el ejemplo de la polimerización en DP = 500 ([l -1] /[(bpy)Ni(COD)]/[Zn(HMDS)2] / [BnOH] / [Ir-1] = 500/1/1/1/0.1). Polímeros en diferentes DPs se pueden preparar también ajustando el monomer masa por consiguiente.
<ol><li>
Preparación de solución l-1 para polimerización
	<ol>
<li>Añadir l-1 (72,2 mg, 375.7 μmol) a un vial de centelleo de 7 mL.</li>
		<li>L-1 en 722 μl de THF anhidro se disuelven.</li>
		<li>Añadir 200 μL de solución de l-1 en otro frasco 7 mL centelleo equipado con una barra de agitación.</li>
		<li>Añada 100 μl de THF anhidro en el vial de centelleo de 7 mL.</li>
		<li>Tapa el frasco y coloque la solución de l-1 en la trampa de frío.</li>
		<li>Apagar la luz de la guantera. PRECAUCIÓN: Es necesario apagar la luz de la guantera para evitar la desactivación de Ir-1 antes de la polimerización.</li>
	</ol>
</li>
	<li>
Enfriamiento de la trampa de frío
	<ol>
<li>Dentro de la caja, coloque un termómetro en la trampa de frío.</li>
		<li>Fuera de la caja, añadir aprox. 500 mL de etanol al matraz dewar.</li>
		<li>Añadir nitrógeno líquido en el frasco de dewar.</li>
		<li>Coloque el frasco de dewar KGW para la trampa de frío.</li>
		<li>Enfriar la trampa de frío a-50 ° C.</li>
		<li>Ponga un revuelo la placa debajo de la fría trampa (ver figura 1).</li>
	</ol>
</li>
	<li>
Realizar la polimerización de la anillo-abertura de photoredox Nota: Antes de iniciar la polimerización, coloque gafas ese bloque azul luz a su alcance. Todas las soluciones de sistema catalizador inmediatamente se sacado del congelador y se agregan sucesivamente en el vial de centelleo de 7 mL que contenga 20 mg de l-1 sin pausa ni interrupción de más de 30 s.<ol>
<li>(Solución de bpy)Ni(COD) (16.4 μL, 0.208 μmol) en el centelleo de 7 mL frasco ampolla de l-1 (preparado en el punto 2.1).</li>
		<li>Añadir solución de2 Zn(HMDS) (24.4 μL, 0.208 μmol) en el frasco.</li>
		<li>Añadir solución de BnOH (22.5 μl, 0.208 μmol) en el frasco.</li>
		<li>Añadir solución de Ir-1 (24.2 μl, 0.0208 μmol) en el frasco y la tapa del frasco.</li>
		<li>Use anteojos de seguridad bloqueo de la luz LED azul. PRECAUCIÓN: Como LED azul luz con una intensidad relativa se utiliza, use gafas de seguridad durante todo el proceso.</li>
		<li>Encender la luz LED azul (34 W) y el ventilador para disipar el calor generado por el LED de luz. Dirigir la luz hacia el frasco en la trampa de frío. (Figura 1)</li>
		<li>Encender el agitador.</li>
		<li>Cubierta de la trampa de frío con papel de aluminio.</li>
		<li>Mantener la temperatura de reacción a-15 ± 5 ° C y añadir nitrógeno líquido cada 15-20 minutos. Nota: El mantenimiento de la temperatura de reacción es importante para la polimerización y control MW.</li>
	</ol>
</li>
</ol>3. supervisar la conversión de monómero por espectros infrarrojo de transformada de Fourier
Nota: Espectros infrarrojos-transformada de Fourier (FTIR) se registran en un espectrómetro FT-IR equipado con accesorio de muestreo diamante ATR y transmisión.
<ol><li>En momentos específicos, añadir una pequeña alícuota de solución de polímero (20 μl) en un vial de centelleo de 7 mL y tapón.</li>
	<li>Sacar la cubeta de la caja de guante.</li>
	<li>Inmediatamente deje caer la solución (3 μL) en el dechado de diamante FTIR-ATR. La solución forma una película dentro de 10 s para la medición de espectro.</li>
	<li>Medir el espectro FTIR de la muestra. Nota: La conversión de monómero se determinó por la relación de intensidad entre 1760 cm-1 y 1805s cm-1: % de conversión = I1760/ (me1760 +1805) (representante de resultados en la figura 2). Generalmente, la polimerización tarda alrededor de 1-8 h DP desde 200 hasta 1000 (cinética detallada se discuten en la referencia 13).</li>
</ol>4. la medida del peso molecular de polímero por cromatografía de permeación de gel
Nota: Experimentos de Gel permeación (GPC) de cromatografía se realizaron en un sistema equipado con una bomba isocrática con desgasificador, detector de dispersión de la luz (MALS) multiangle láser (láser de GaAs 30 mW a λ = 690 nm) y detector de índice de refracción diferencial (DRI) con una fuente de luz de 690 nm. Separaciones se realizan utilizando columnas de exclusión de tamaño conectados en serie (100 Å, 500 Å, 103 Å y 10 columnas de4 Å, 5 μm, 300 × 4,6 mm) a 35 ° C utilizando THF como fase móvil a un caudal de 0,35 mL/min. El peso molecular de polímero (MW) y la distribución de peso molecular (Ð) se determinan mediante el modelo de Zimm ajuste de datos MALS-DRI. La presencia de metal en el polímero no afecta los resultados de medición de la GPC.
<ol><li>Quitar una pequeña alícuota de solución de polímero (50 μL) de la caja de guante.</li>
	<li>Añada 100 μl de THF en el frasco.</li>
	<li>Inyectar la muestra en el dechado de la GPC.</li>
	<li>Analizar el resultado una vez terminado el plazo de la GPC. Nota: El polímero debe monodispersados con estrecho Đ (representante de resultados en la figura 3). El polímero (20 mg) puede ser secado y lavado por el éter dietílico 1 mL que contiene 1% de metanol HOAc y 1 mL, que puede quitar el 87% de Ni y el 50% de los complejos de Zn, determinados por espectrometría de plasma acoplado inductivamente (ICP-MS).</li>
</ol>

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Los autores no declaran a intereses financieros en competencia. Una patente provisional (los E.E.U.U. patente aplicación No: 62/414.016) se ha presentado referente a los resultados presentados en este trabajo.

El paso crítico en el protocolo es mantener la temperatura de reacción a-15 ± 5 ° C. Todas las soluciones de catalizadores y monómeros OCA deben almacenarse en un congelador de guantera a-35 ° C antes de la polimerización. Los viales de reacción tienen que ser previamente enfriado en la trampa de frío. Durante la reacción, porque la luz disipa el calor, es necesario controlar la reacción cada 15-20 minutos. Una vez que se eleva la temperatura hasta-10 ° c, nitrógeno líquido debe añadirse en el dewar para e...

Poli (α-hidroxi ácido) (PAHA) es una clase importante de polímeros biodegradables y biocompatibles con aplicaciones que van desde dispositivos biomédicos para los materiales de embalaje. 1 , 2 PAHAs aunque pueden elaborarse directamente por la policondensación de ácidos α-hydroxy, pesos moleculares (MW) de los PAHAs resultantes son generalmente bajos. 3 la polimerización de la anillo-abertura (ROP) de lactonas (láctido y glicólido) es una alternativa sintético que proporciona el mejor control en MWs y la distribución de peso molecular (Đ) de policondensación. Sin embargo, la falta de funcionalidad de cadena lateral PAHAs y lactonas limita la diversidad de propiedades físicas y químicas y sus aplicaciones. 4 , 5 desde el año 2006, 1, 3-dioxolane-2,4-diones, supuesto O- carboxyanhydrides (OCAs), que se puede preparar con una gran variedad de funcionalidades de cadena lateral,6,7,8, 9 , 10 , 11 , 12 , 13 han surgido como una clase alternativa de monómeros muy activos para la polimerización del poliéster. 14 , 15
Sistemas catalíticos para la retinopatía de la prematuridad de OCAs se pueden categorizar en organocatalizadores,8,12,16,17 catalizadores organometálicos12,18,19 ,20,21 y biocatalizadores. 22 en general, la retinopatía de la prematuridad de OCAs, promovido por organocatalyst procede de una manera más o menos incontrolada, por ejemplo epimerization (es decir, falta de stereoregularity) de OCAs con grupos electrón-retirarse,8,17 MWs impredecibles, o cinética de polimerización lenta. 13 para abordar estos problemas, un complejo activo de alcóxido de Zn fue desarrollado para la retinopatía de la prematuridad de OCAs. 12 well-controlled ROPs se lograron en un bajo grado de polimerización (DP) sin Epimerización. Sin embargo, este catalizador Zn alcóxido eficiente no puede producir polímeros con un alto grado de polimerización (DP ≥ 300). 13
Recientemente hemos reportado un enfoque prometedor que mejora grandemente la personalización y la eficacia de síntesis PAHA (figura 1). 13 nos fusionamos catalizadores de Ni/Ir photoredox que promueven la descarboxilación de la OCA con zinc alcóxido para mediar la polimerización de la anillo-abertura de OCAs. El uso de baja temperatura (-15 ° C) y photoredox catálisis Ni/Ir sinérgicamente acelera la apertura y descarboxilación de la OCA para la propagación de la cadena evitando las reacciones laterales indeseadas, por ejemplo, la formación de Ni-carbonilo. 23 , 24 con reductora con complejo Ni el alcóxido de Zn activo se encuentra en el terminus de la cadena de propagación de la cadena. 13
En este protocolo, añadimos el preparado fresco (bpy)Ni(COD) (bpy = 2, 2'-bipiridilo, COD = 1,5-cyclooctadiene), Zn(HMDS)2 (HMDS = hexamethyldisilazane),25 el alcohol bencílico (BnOH) y (6 ) Ir [dF (CF3) ppy]2(dtbbpy) PF Ir-1, dF (CF3) ppy = 2-(2, 4-difluorophenyl) -5-(trifluorometil) piridina, dtbbpy = 4, 4' - di -terc- butil-2, 2'-bipyridine) en el monómero l-1 solución26 en una guantera con una trampa de frío, en la presencia de un luz azul (400-500 nm) y un ventilador para mantener la temperatura (figura 1). La temperatura se mantiene a-15 ° C ± de 5 ° C durante la polimerización. La conversión de OCA es supervisada por espectroscopia infrarroja de transformada de Fourier. El polímero resultante MWs y Đs se caracteriza por una cromatografía de permeación de gel (GPC). El homodecoupling 1estudio de RMN de H determina si el polímero obtenido es isotáctica o no. Como la mayoría de productos químicos son altamente sensibles a la humedad, el protocolo detallado de vídeo está destinado a nuevos agentes evitar errores asociados con la retinopatía de la prematuridad de OCAs de photoredox.

<table><tbody><tr><td>Ni(COD)&lt;sub&gt;2&lt;/sub&gt;</td><td>Strem</td><td>28-0010</td><td>Stored in the glove box freezer.</td></tr><tr><td>2,2&amp;prime;-bipyridine</td><td>Strem</td><td>07-0290</td><td>Stored in the glove box freezer.</td></tr><tr><td>Zn(HMDS)&lt;sub&gt;2&lt;/sub&gt;</td><td>N/A</td><td>N/A</td><td>Synthesized following reported procedures.&lt;sup class=&quot;xref&quot;&gt;25&lt;/sup&gt; Stored in the glove box freezer.</td></tr><tr><td>Benzyl alcohol</td><td>Sigma-Aldrich</td><td>402834</td><td>Stored with 4&amp;Aring; molecular sieve</td></tr><tr><td>Ir[dF(CF&lt;sub&gt;3&lt;/sub&gt;)ppy]&lt;sub&gt;2&lt;/sub&gt;(dtbbpy)PF&lt;sub&gt;6&lt;/sub&gt;</td><td>Strem</td><td>77-0425</td><td>Stored in the glove box freezer.</td></tr><tr><td>THF</td><td>Sigma-Aldrich</td><td>34865</td><td>Dried by alumina columns and stored with 4&amp;Aring; molecular sieve in the dark bottle in the glove box.</td></tr><tr><td>Ethanol</td><td>Sigma-Aldrich</td><td>793175</td><td></td></tr><tr><td>GPC with an isocratic pump</td><td>Agilent</td><td>Agilent 1260 series</td><td></td></tr><tr><td>Dawn Heleos II Light Scatterer</td><td>Wyatt</td><td></td><td></td></tr><tr><td>Optilab rEX differential refractive index detector</td><td>Wyatt</td><td></td><td></td></tr><tr><td>Size exclusion columns</td><td>Phenomenex</td><td></td><td></td></tr><tr><td>Glass Scintillation Vials - 7 ml</td><td>VWR</td><td></td><td></td></tr><tr><td>FTIR spectrometer</td><td>Agilent</td><td></td><td></td></tr><tr><td>Stir bars</td><td>VWR</td><td>58948-091</td><td></td></tr><tr><td>Balance</td><td></td><td></td><td></td></tr><tr><td>Glove box</td><td>Mbraun</td><td>Labstar Pro</td><td></td></tr></tbody></table>

controlled photoredox ring-opening polymerization of o-carboxyanhydrides mediated by ni/zn complexes

Aquí, describimos un protocolo eficaz que combina catálisis de Ni/Ir photoredox con el uso de un alcóxido de Zn para la polimerización de apertura eficiente, lo que permite la síntesis de isotáctico poli (α-hidroxi ácidos) con peso molecular esperado (> 140 kDa) y estrecha distribución de peso molecular (Mw/Mn < 1,1). Esta polimerización de la anillo-abertura es mediada por complejos de Ni y Zn en presencia de un iniciador de alcohol y un photoredox catalizador Ir, irradiado por un LED azul (400-500 nm). La polimerización se realiza a baja temperatura (-15 ° C) para evitar reacciones secundarias no deseadas. El consumo de monómero completo puede lograrse dentro de 4 a 8 horas, proporcionando un polímero cerca el peso molecular esperado con distribución de pesos moleculares estrechas. El peso de molecular medio en número resultante muestra una correlación lineal con el grado de polimerización hasta 1000. El homodecoupling 1estudio de RMN de H confirma que el polímero obtenido es isotáctica sin Epimerización. Esta polimerización se divulga adjunto ofrece una estrategia para lograr la polimerización de carboxyanhydrides - rápida, controlada Opara preparar stereoregular poli (α-hidroxi ácidos) y sus copolímeros con varios grupos funcionales de la cadena lateral.

La conversión de OCA es supervisada por espectroscopia infrarroja de transformada de Fourier, como se muestra en la figura 2. El pico en 1805 cm-1 se asigna como el tramo de enlace anhídrido de OCA; el pico en 1760 cm-1 corresponde a la formación del enlace éster en el polímero. Una vez que el pico de monómero a 1805 cm-1 desaparece completamente, se termina la polimerización.
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Watch this Scientific Journal Video about Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes at JoVE.com

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Se presenta un protocolo para la polimerización de apertura controlada photoredox de O- carboxyanhydrides mediada por complejos de Ni/Zn.

Controla la polimerización de apertura de Photoredox de O- Carboxyanhydrides mediada por complejos de Ni/Zn

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

controlled-photoredox-ring-opening-polymerization-o-carboxyanhydrides

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JoVE Journal

Chemistry

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

8.0K vistas.  Nanjing University of Posts and Telecommunications. Se presenta un protocolo para la polimerización de apertura controlada photoredox de O- carboxyanhydrides mediada por complejos de Ni/Zn.

Video: Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel &#945;-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel &#945;-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

A protocol for the high-throughput analysis of polymerization catalyst, chain transfer polymerizations, polyethylene characterization, and reaction kinetic analysis is presented.

Las polimerizaciones de etileno utilizando reactores de presión paralelas y un análisis cinético de la cadena de transferencia de polimerización

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel ...

Investigación

Química

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

A method for the atom transfer radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst is described.

Transferencia átomo de polimerización por radicales de monómeros funcionalizados vinilo Uso de perileno como fotocatalizador luz visible

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The ...

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of solid-phase synthesis, regenerating Michael (REM) linker strategies, and 1,3-dipolar cycloaddition, a library of structurally similar heterocycles, both with and without a spirocyclic center, can be constructed. The main advantages of the solid-support synthesis are as follows: first, each reaction step can be driven to completion using a large excess of reagents resulting in high yields; next, the use of commercially available starting materials and reagents keep the costs low; finally, the reaction steps are easy to purify via simple filtration. The REM linker strategy is attractive because of its recyclability and traceless nature. Once a reaction scheme is completed, the linker can be reused multiple times. In a typical solid-phase synthesis, the product contains either a part of or the whole linker, which can prove undesirable. The REM linker is &#34;traceless&#34; and the point of attachment between the product and the polymer is indistinguishable. The high diastereoselectivity of the intramolecular 1,3-dipolar cycloaddition is well documented. Limited by the insolubility of the solid support, the reaction progression can only be monitored by a change in the functional groups (if any) via infrared (IR) spectroscopy. Thus, the structural identification of intermediates cannot be characterized by conventional nuclear magnetic resonance (NMR) spectroscopy. Other limitations to this method stem from the compatibilities of the polymer/linker to the desired chemical reaction scheme. Herein we report a protocol that allows for the convenient production of spirocyclic heterocycles that, with simple modifications, can be automated with high-throughput techniques.

Here we present a protocol to demonstrate an efficient method for the synthesis of spirocyclic heterocycles. The five-step process utilizes solid-phase synthesis and regenerating Michael linker strategies. Generally difficult to synthesize, we present a customizable method for the synthesis of spirocyclic molecules otherwise inaccessible to other modern approaches.

Síntesis en fase sólida de oximas espirocícliclos [4,4]

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of ...

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes and determine the corresponding photochemical mechanism. Then, we describe a protocol to perform ring-opening metathesis polymerization (ROMP) in solution and in miniemulsion using this NHC-photogenerating system. To photogenerate IMes, a system comprising 2-isopropylthioxanthone (ITX) as the sensitizer and 1,3-dimesitylimidazolium tetraphenylborate (IMesH+BPh4-) as the protected form of NHC is employed. IMesH+BPh4- can be obtained in a single step by anion exchange between 1,3-dimesitylimidazolium chloride and sodium tetraphenylborate. A real-time steady-state photolysis setup is described, which hints that the photochemical reaction proceeds in two consecutive steps: 1) ITX triplet is photo-reduced by the borate anion and 2) subsequent proton transfer takes place from the imidazolium cation to produce the expected NHC IMes. Two separate characterization protocols are implemented. Firstly, CS2 is added to the reaction media to evidence the photogeneration of NHC through formation of the IMes-CS2 adduct. Secondly, the amount of NHC released in situ is quantified using acid-base titration. The use of this NHC photo-generating system for the ROMP of norbornene is also discussed. In solution, a photopolymerization experiment is conducted by mixing ITX, IMesH+BPh4-, [RuCl2(p-cymene)]2 and norbornene in CH2Cl2, then irradiating the solution in a UV reactor. In a dispersed medium, a monomer miniemulsion is first formed then irradiated inside an annular reactor to produce a stable poly(norbornene) latex.

We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.

Photogeneration de carbenos N-heterocíclicos: aplicación en fotoinducida anillo-abertura polimerización de metátesis

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes ...

[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the activation of a broad variety of organic halides, including unactivated ones. These can then participate in various radical transformations such as reduction and cyclization reactions, as well as in the direct arylation of several (hetero)arenes. These transformations provide a straightforward access to a range of small molecules of interest in synthetic chemistry, as well as to biologically active natural products. Altogether, [(DPEPhos)(bcp)Cu]PF6 acts as a convenient photoredox catalyst which appears to be an attractive, cheap and complementary alternative to the state-of-the-art iridium- and ruthenium-based photoredox catalysts. Here, we report a detailed protocol for the synthesis of [(DPEPhos)(bcp)Cu]PF6, as well as NMR and spectroscopic characterizations, and we illustrate its use in synthetic chemistry for the direct arylation of (hetero)arenes and radical cyclization of organic halides. In particular, the direct arylation of N-methylpyrrole with 4-iodobenzonitrile to afford&#160;4-(1-methyl-1H-pyrrol-2-yl)benzonitrile and the radical cyclization of N-benzoyl-N-[(2-iodoquinolin-3-yl)methyl]cyanamide to afford natural product luotonin A are detailed. The scope and limitations of this copper-based photoredox catalyst are also briefly discussed.

[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Detailed and general protocols are presented for the synthesis of [(DPEPhos)(bcp)Cu]PF6, a general copper-based photoredox catalyst, and for its use in synthetic chemistry for the direct arylation of C-H bonds in (hetero)arenes and radical cyclization of organic halides.

[(DPEPhos) (BCP) cu] PF6: un catalizador Photoredox general y ampliamente aplicable basado en cobre

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the ...

Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions

The interest on nitrogen-containing heterocycles has expanded rapidly in the synthetic community since they are important motifs for new drugs. Traditionally, they were synthesized through thermal cycloaddition reactions, whereas today, photocatalysis is preferred due to the mild and efficient conditions. With this focus, a new photocatalytic method for the synthesis of nitrogen-containing heterocycles is highly desired. Here, we report a protocol for the biosynthesis of cercosporin, which could function as a metal-free photocatalyst. We then illustrate cercosporin-photocatalyzed protocols for the synthesis of nitrogen-containing heterocycles 1,2,3-thiadiazoles through annulation of azoalkenes with KSCN, and synthesis of 1,4,5,6-tetrahydropyridazines [4+2] through cyclodimerization of azoalkenes under mild conditions, respectively. As a result, there is a new bridge between the microbial fermentation method and organic synthesis in a mild, cost-effective, environmentally friendly and sustainable manner.

New routes for the synthesis of nitrogen-containing heterocycles utilizing cercosporin as a metal-free photocatalyst were developed.

Cercosporina-Fotocatalizado [4+1]- y [4+2]-Anulaciones de Azoalkenes bajo condiciones leves

The interest on nitrogen-containing heterocycles has expanded rapidly in the synthetic community since they are important motifs for new drugs. ...

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. Achieving a closed-loop polymer economy via chemical recycling to monomer (CRM) is one such promising route. Our group recently reported a new CRM system based on polymers prepared by ring-opening metathesis polymerization (ROMP) of trans-cyclobutane fused cyclooctene (tCBCO) monomers. This system offers several key advantages, including the ease of polymerization at ambient temperatures, quantitative depolymerization to monomers under mild conditions, and a broad range of functionalities and thermomechanical properties. Here, we outline detailed protocols for the preparation of tCBCO-based monomers and their corresponding polymers, including the preparation of elastic polymer networks and compression molding of linear thermoplastic polymers. We also outline the preparation of high ring strain E-alkene tCBCO monomers and their living polymerization. Finally, the procedures for the depolymerization of linear polymers and polymer networks are also demonstrated.

Here, we describe protocols for the preparation of trans-cyclobutane fused cyclooctenes (tCBCO),&#160;their polymerization to prepare depolymerizable olefinic polymers, and the depolymerization of these polymers under mild conditions. Additionally, protocols for the preparation of depolymerizable networks and compression molding of rigid linear plastics based on this system are described.

Polímeros olefínicos despolimerizables basados en monómeros de cicloocteno de anillo fundido

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. ...

Photochemical Initiation Of Radical Polymerization Reactions

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to generate polystyrene, which is an important commodity plastic. We will learn the fundamentals of photochemistry and use simple photochemistry to initiate radical polymerization reactions. Specifically, in this module we will examine the photochemistry of benzoyl peroxide and its role as a photo-initiator of styrene polymerization reactions. In the described experiments, we will investigate the role of wavelength, photon absorption, and excited state structure on the efficiency (measured as quantum yield) of photochemical reactions.

Iniciación fotoquímica de reacciones de polimerización por radicales libres

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to ...

Educación

JoVE Science Education

Química inorgánica

Acid-Catalyzed Ring-Opening of Epoxides

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The reaction follows the SN2 mechanism, and the protonated oxygen, unlike other leaving groups, does not detach from the molecule. The regiochemistry of the products formed is governed by either steric or electronic effects. In the case of an asymmetrical epoxide bearing a primary and a secondary carbon, the steric effect dominates and favors the nucleophilic attack at a less-hindered carbon. However, in epoxides where one of the carbons is tertiary, the electronic effect comes into play and favors the attack at a more-hindered carbon. The stereochemistry of the products is similar to an SN2 reaction, where the nucleophile attacks anti to the leaving group. Notably, the anti-attack at a chiral carbon causes an inversion of configuration.

Apertura de Anillo de Epóxidos Catalizada por Ácido

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the ...

JoVE Core

Química Orgánica

Unidad 1

Éteres, Epóxidos, Sulfuros

TÉRMINOS Y CONCEPTOS CLAVES

Base-Catalyzed Ring-Opening of Epoxides

Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile or a base. A variety of nucleophiles like sodium hydroxide, sodium alkoxide, sodium hydrosulfide, sodium cyanide, lithium aluminum hydride, and Grignard reagent can open the epoxide ring. The nucleophilic attack on the epoxide ring proceeds via an SN2 mechanism and involves an alkoxide intermediate. The product formed in base-catalyzed reactions shows SN2-like stereoselectivity and regioselectivity. The nucleophile attacks at the less-hindered carbon and anti to the leaving group, leading to the inversion of configuration at a chiral center. In contrast to epoxides, acyclic ethers do not undergo direct nucleophilic substitutions, as the reaction is thermodynamically unfavorable.

Apertura de Anillo de Epóxidos Catalizada por Base

Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of ...