A functionalized graphene oxide and nano-zeolitic imidazolate framework composite as a highly active and reusable catalyst for [3+3] formal cycloaddition reactions

We report a facile coordination-induced growth approach to fabricate a SO3H-functionalized graphene oxide and nanosized zeolitic imidazolate framework composite (ZIF-8@SO3H-GO) under mild conditions. The interactions between the functional groups on the sheets of GO with Zn(II) ions of the ZIF-8 precursor initiated the nucleation and growth of ZIF-8 on the GO and meanwhile nanosized ZIF-8 particles were well dispersed on the sheets of GO. Owing to the co-existing basic imidazole moieties from ZIF-8 and the SO3- and CO2--functional groups on the sheets and Zn2+ ions from ZIF-8 in this Lewis acid rich composite, it exhibited high catalytic reactivity and selectivity in [3 + 3] formal cycloaddition reactions that consist of two-step Knoevenagel-type condensation and electrocyclic ring-closure to give various synthetically valuable pyranyl heterocycles. Interestingly, it was especially advantageous for the large sized reactants. The results indicated that it displayed 2 times higher reactivity compared to ZIF-8 nanoparticles due to the newly formed mesopores in the junctions between GO sheets and ZIF-8 nanoparticles. More importantly, it could be conveniently recovered and recycled 10 times without the loss of activity.