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Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes
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Orígenes de la Regioselectividad en la Sustitución Alilica Catalizada por Iridio
Sherzod T Madrahimov1, Qian Li2, Ankit Sharma2
1Department of Chemistry, University of Illinois , 600 South Mathews, Urbana, Illinois 61801, United States.
Journal of the American Chemical Society
|October 27, 2015
Resumen
Los catalizadores de iridio con ligandos de trifenilfosfito muestran una alta regioselectividad para los productos ramificados. Las interacciones no covalentes, no estéricas, explican esta selectividad en las reacciones catalíticas.
Área de la Ciencia:
- Química organometálica
- Catálisis
- Síntesis orgánica
Sus antecedentes:
- La regioselectividad en la catálisis es crucial para sintetizar productos orgánicos específicos.
- Los complejos de iridio con trifenilfosfito (P(OPh) 3 son conocidos por su alta regioselectividad.
- Comprender el origen de esta selectividad es clave para el diseño de catalizadores.
Objetivo del estudio:
- Investigar el origen de la regioselectividad en las reacciones catalizadas por iridio que favorecen los productos ramificados.
- Identificar las especies catalíticas activas y los productos intermedios clave.
- Para aclarar los factores que rigen la selectividad en los sistemas de iridio frente al paladio.
Principales métodos:
- Estudios detallados de complejos de iridio con ligandos de trifenilfosfito.
- Generación y caracterización de complejos de aliliridio.
- Estudios computacionales para evaluar las interacciones electrónicas y no covalentes.
- Comparación con los complejos de allilpalladio.
Principales resultados:
- El catalizador activo se forma por ciclometalización de P ((OPh) 3 , con las especies ligadas a P,C como estado de reposo.
- Los complejos de Allyliridium son productos intermedios competentes.
- Factores como la carga y la longitud del enlace no diferencian la selectividad entre el iridio y el paladio.
- Los estudios computacionales indican que las interacciones no covalentes débiles y atractivas favorecen la formación de productos ramificados con iridio.
Conclusiones:
- Las interacciones no covalentes atractivas débiles, como las interacciones del aceptor de enlaces H con enlaces vinilo C-H, son críticas para la regioselectividad de los catalizadores de iridio.
- Estas fuerzas atractivas, junto con los efectos estéricos repulsivos, son esenciales para racionalizar la selectividad catalítica.
- Los resultados ponen de relieve la importancia de considerar las interacciones no covalentes en el desarrollo de catalizadores.
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