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Estudio mecanicista de la fase de solución y de la estructura en estado sólido de un catión complejo de inclusión de

Albert C Fahrenbach¹, Jonathan C Barnes, Don Antoine Lanfranchi

¹Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.

Journal of the American Chemical Society

|December 14, 2011

Resumen

El anillo de ciclóbis (((paraquat-p-fenileno) (CBPQT (((2(•+))) forma complejos de inclusión estables con cationes radicales de 1,1′-dialquilo-4,4′-bipiridinio (BIPY (((•+)). Este reconocimiento radical-radical avanza en la comprensión de las interacciones moleculares y las moléculas mecánicamente entrelazadas.

Área de la Ciencia:

Química supramolecular de las moléculas.
Ciencia de los materiales Ciencia de los materiales.
Química orgánica es la química orgánica.

Sus antecedentes:

El ciclóbis (paraquat-p-fenileno) (CBPQT) es un anillo dicationico diradical.
Los cationes radicales 1,1′-dialquilo-4,4′-bipiridinium (BIPY(•+)) son huéspedes comunes en la química huésped-huésped.

Objetivo del estudio:

Investigar de manera mecanicista y cuantitativa la formación de complejos de inclusión entre los huéspedes CBPQT{2} y BIPY{+}.
Para dilucidar las propiedades estructurales, termodinámicas y cinéticas de estos complejos trisradical.

Principales métodos:

Cristalografía de rayos X de un solo cristal para determinar estructuras complejas.
Cálculos mecánicos cuánticos para apoyar los hallazgos estructurales.
Calorimetría de titulación isotérmica (ITC) y espectroscopia UV/vis para la estabilidad termodinámica.
Espectroscopia de flujo detenido para estudios cinéticos de asociación y disociación.
Voltametría cíclica (CV) de velocidad de escaneo variable para detalles mecánicos electroquímicos.

Principales resultados:

Se formaron dos complejos trisrádicos, CBPQT(2(•+))MV(•+) y CBPQT(2(•+))V(•+).
La cristalografía de rayos X reveló una disposición centrosimétrica de MV ((•+) dentro de la cavidad CBPQT ((2(•+))), formando pilas de cationes radicales continuas.
Los cálculos mecánicos cuánticos indicaron la asimetría electrónica en el SOMO debido a las interacciones de emparejamiento de radicales, que persisten en la solución.
Las espectroscopias ITC y UV/vis arrojaron constantes de unión para CBPQT ((2(•+)) MV(•+) de (5.0 ± 0.6) × 10^4 M−1 y (7.9 ± 5.5) × 10^4 M−1, respectivamente.
La espectroscopia de flujo detenido determinó las tasas de asociación (k_f = (2.1 ± 0.3) × 10^6 M−1 s−1) y disociación (k_b = 250 ± 50 s−1) para CBPQT(2(•+)) MV(•+).
Los estudios electroquímicos revelaron un intermediario tetracationico bisrádico, con una disociación lenta (k_b = 10 ± 2 s−1) para el huésped V(•+).

Conclusiones:

El anillo CBPQT exhibe capacidades únicas de reconocimiento tanto para los cationes radicales BIPY como para los invitados potencialmente ricos en electrones π.
Estos hallazgos establecen una base para utilizar el reconocimiento radical-radical en moléculas mecánicamente entrelazadas.
El estudio mejora la comprensión fundamental de las interacciones BIPY ((•+) radical-radical tanto en la solución como en los estados sólidos.

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