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Mecanismo de eliminación del beta-hidrógeno de los complejos de alóxido de iridio ((I) plano cuadrado con ligandos
J Zhao1, H Hesslink, J F Hartwig
1Contribution from the Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8017, USA.
Journal of the American Chemical Society
|July 27, 2001
Resumen
Este estudio revela que la eliminación de beta-hidrógeno de los complejos de iridio alkoxo es un proceso reversible. Este hallazgo contrasta con los modelos anteriores y ofrece nuevos conocimientos sobre las vías de reacción organometálica.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Mecanismos de reacción Mecanismos de reacción
- Coordinación Química de la Coordinación
Sus antecedentes:
- Los complejos alcoxo planares cuadrados, [Ir(CO) ((PPh3) 2 ((OR) ], exhiben una estabilidad y reactividad únicas.
- Comprender la eliminación de beta-hidrógeno es crucial para la catálisis y la química sintética.
Objetivo del estudio:
- Para dilucidar el mecanismo de la eliminación de beta-hidrógeno de los complejos de iridio alkoxo.
- Para investigar la influencia de la concentración de fosfina y los sustituyentes en la vía de reacción.
- Para comparar el mecanismo observado con los modelos existentes para la eliminación de alcóxido y alquilo.
Principales métodos:
- Estudios mecánicos que incluyen análisis cinético, efectos isotópicos y experimentos de racemicidad.
- La termólisis de los complejos de iridio alkoxo en presencia de trifenilfosfina (PPh3).
- Variación de la concentración de fosfina y el disolvente para sondear la cinética de la reacción.
Principales resultados:
- Se encontró que la eliminación de beta-hidrógeno era reversible, con constantes de velocidad mínimamente afectadas por los sustituyentes de beta-carbono.
- Las órdenes de reacción con respecto a la concentración de fosfina variaron, lo que indica una cinética compleja.
- Se observó un efecto de isótopo cinético primario en la intersección en y de las parcelas 1/k(obs) vs [PPh3].
Conclusiones:
- Un mecanismo que implica la eliminación reversible de beta-hidrógeno seguida de un desplazamiento asociativo por PPh3 explica los datos observados.
- Esta vía difiere de los mecanismos de eliminación directa, protóticos o binucleares propuestos.
- La eliminación del alcóxido puede proceder a través de vías análogas a los complejos de alquilo, desafiando suposiciones anteriores.
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