Cu(CH3CN)4PF6 immobilized on halloysite as efficient heterogeneous catalyst for oxidation of allylic C–H bonds in olefins under mild reaction condition

Abstract

Considering the importance of oxidation of allylic C–H bonds in olefins and the unresolved challenging issues, such as long reaction time and the large quantity of catalyst required, and encouraged by the excellent performance of halloysite as a catalyst support, a novel catalytic system was developed to promote this reaction efficiently. To prepare the catalyst, halloysite was first functionalized with ionic liquid then reacted with 2-aminopyrimidine to afford a potential support, Hal-P. The latter was then used for in situ immobilization of Cu(CH3CN)4PF6 and applied to promote the reaction of cycloolefin and tert-butyl p-nitrobenzoperoxoate under mild reaction condition. The results showed that the nature of copper could play an important role in the catalytic activity. Moreover, the presence of ionic liquid and 2-aminopyrimidine in the structure could improve the activity of the final catalyst. Notably, low amounts of catalyst could catalyze the reaction to afford corresponding allylic esters in good yield. It was also found that the reaction was size selective and that cyclic olefins with lower strain could undergo this reaction more effectively. Study of the recyclability of the catalyst confirmed that it was recyclable and could be recovered and recycled for five consecutive reaction runs.