Activity enhancement in cyanation of aryl halides through confinement of ionic liquid in the nanospaces of SBA-15-supported Pd complex

Abstract

A novel and practical ionic-liquid mediated route for the synthesis of various aromatic nitriles has been developed via the cyanation of aryl halides with K₄[Fe(CN)₆] as a low cost, non-toxic and easily handled cyanating reagent in the presence of SBA-15 functionalized palladium complex partially confined with ionic liquids (IL@SBA-15-Pd) as the catalyst. Among the various ionic liquids tested in the cyanation reaction, 1-butyl-3-methylimidazolium hexafluorophosphate was found to provide the best medium for Pd-catalyzed cyanation of aryl halides. A variety of electron-rich and electron-poor aryl iodides and bromides gave the corresponding benzonitrile derivatives in good yield. Moreover, the catalyst was reused in four consecutive cycles with consistent catalytic activity. It was found that the presence of ionic liquid in the mesochannels of the mesoporous support not only provides a means of stabilizing Pd nanoparticles during the reaction but also the salient phase transfer feature of the imidazolium moieties may also serve as handles for faster penetration of Fe(CN)₆³⁻ into the system pores to achieve highly concentrated reaction sites in close proximity to the catalytic (Pd NPs) centers, which resulted in an enhancement of the catalyst activity performance.