A Palladium Complex Dispersed in Ionic Liquid as an Efficient Catalytic Combination for the Synthesis of Benzazoles

Abstract

Ethyl methyl imidazolium hexafluorophosphate, [EMIM] PF6, mediated procedure for the synthesis of benzazoles catalyzed by a palladium benzimidazole Schiff base complex was efficiently demonstrated. The catalyst showed excellent efficiency in C-N, C-O, and C-S coupling reactions forming benzazoles i.e. benzimidazoles, benozoxazoles and benzothiazoles, respectively, via hydrogen transfer method in aerobic conditions. The hydrogen transfer route for this catalytic process was confirmed by testing the transfer hydrogenation ability of the catalyst in several hydrogenation reactions of converting aldehydes/ketones into alcohols. The efficacy of catalytic system was investigated by carrying out the synthesis of benzazoles in two sets of reactions, by varying the solvents. In the first set of reactions water was used as the solvent and in the second, a mixture of [EMIM] PF6: water (1:1) was used and the results were compared. In water, the catalyst facilitated the reactions yielding up to 82% in 8 h; whereas, in the ionic liquid-water mixture as solvent, the competence of the catalyst was accelerated, resulting up to 94% yield in a shorter duration of 2 h. Moreover the catalyst in the ionic liquid: water mixture was recyclable and was reused up to 5 times effectively.