Article

 

On the Origin of the Conformationally Non–Interconvertable Isomers of Bisphenyldirhodium(III) Caprolactamate^*

 

Jian–Hua Xie and Michael P. Doyle^*

 

Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, U.S.A. ^*Responsible author.

 

Received July 11, 2009
Accepted September 24, 2009

 

Abstract

A plausible explanation for the unprecedented formation of two conformational isomers of bisphenyldirhodium(III) caprolactamate is presented. The presence of acetic acid during the coupling process leading to the formation of bisphenyldirhodium(III) caprolactamate is shown to increase the propeller conformer at the expense of the biplanar conformer, Acetic acid is also found to catalyze the decomposition of bisphenyldirhodium(III) caprolactamate with the propeller conformation reacting at a rate that is more than ten times greater than that for the biplanar conformation. We speculate that protonation of one of the caprolactamate ligands changes the orientation of the phenyl ring in its approach to rhodium in the product–forming step of the arylation reaction leading to the formation of the two conformational isomers.

Key words: Rhodium, Conformational Isomers, Acetic Acid, Phenylrhodium, Coupling.

 

Resumen

Se presenta evidencia sobre una posible explicación de la novedosa formación de dos isómeros conformacionales del complejo caprolactama bisfenildirodio(III). Se muestra que la presencia de ácido acético durante el proceso de acoplamiento conduce al incremento en la formación del complejo caprolactama bisfenildirodio(III) en su confórmero de propela a expensas del confórmelo biplanar. También se demuestra que el ácido acético cataliza la descomposición del complejo caprolactama bisfenildirodio(III) en su forma de propela a una rapidez diez veces mayor que el complejo en forma biplanar. Se especula que la protonación de uno de los ligantes caprolactamas cambia la orientación del anillo bencénico al acercarse al rodio durante la etapa de formación del producto en la reacción de arilación que conduce a los dos isómeros conformacionales.

Palabras clave: Rodio, isómeros conformacionales, ácido acético, fenilrodio, acoplamiento.

 

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Acknowledgments.

We are grateful to the National Science Foundation of the United States for their support of this research.

 

References

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Note

^*Dedicated to the memory of Ernest L. Eliel.