Catalizadores quirales de rutenio altamente activos para la metátesis de olefinas de cierre de anillo asimétrico
Timothy W Funk1, Jacob M Berlin, Robert H Grubbs
1Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Journal of the American Chemical Society
|February 9, 2006
Resumen
Los nuevos catalizadores quirales de carbenos N-heterocíclicos permiten una metátesis asimétrica de cierre de anillo (ARCM) eficiente para sintetizar anillos de cinco a siete miembros con alta enantioselectividad. La adición de yoduro de sodio aumenta significativamente el rendimiento de muchos sustratos.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- La catálisis es la catálisis.
- Síntesis asimétrica de síntesis.
Sus antecedentes:
- La metátesis de olefinas es una herramienta poderosa para la formación de enlaces C=C.
- Los carbenos N-heterocíclicos quirales (NHC) son ligandos emergentes para la catálisis de metales de transición.
- El desarrollo de variantes asimétricas eficientes de reacciones conocidas es crucial para la síntesis de moléculas quirales.
Objetivo del estudio:
- Para sintetizar nuevos ligandos quirales monodentados de carbenos N-heterocíclicos (NHC, por sus siglas en inglés).
- Para aplicar estos catalizadores basados en NHC a la metástasis de cierre de anillo asimétrico (ARCM).
- Para investigar el efecto de la estructura del catalizador y los aditivos en la enantioselectividad.
Principales métodos:
- Síntesis de ligandos NHC monodentados quirales y sus catalizadores metálicos correspondientes.
- Aplicación de estos catalizadores en reacciones asimétricas de metátesis de anillo cerrado.
- Optimización de las condiciones de reacción, incluyendo el uso de aditivos como el yoduro de sodio.
Principales resultados:
- Desarrolló catalizadores de metástasis de olefinas quirales altamente reactivos basados en NHC.
- Se obtienen altas enantioselectividades (hasta el 92% ee) en la formación de anillos de cinco a siete miembros.
- Se demostró un efecto positivo significativo del yoduro de sodio en la enantioselectividad para varios sustratos.
- Se identificó un catalizador (5a) eficaz a bajas cargas (< o = 1 mol %) sin NaI.
Conclusiones:
- Los catalizadores NHC quirales son efectivos para ARCM, coincidiendo con la reactividad de las contrapartes achirales.
- El yoduro de sodio juega un papel crítico en la mejora de la enantioselectividad para muchos sustratos.
- El diseño del catalizador, incluidas las modificaciones estéricas, influye en el rendimiento del ARCM.
- Se discutieron conocimientos mecánicos sobre el efecto del yoduro de sodio y las vías de ARCM.
Videos de Conceptos Relacionados
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
01:12Acid Halides to Esters: Alcoholysis
Alcoholysis is a nucleophilic acyl substitution reaction in which an alcohol functions as a nucleophile. Acid halides react with alcohol to produce esters. The mechanism proceeds in three steps:
01:13Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis
Hydrolysis of esters under acidic conditions proceeds through a nucleophilic acyl substitution. In the presence of excess water, the reaction proceeds in a reversible manner, forming carboxylic acids and alcohols.
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
01:22Heterogeneous Catalysis
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...