Heterogeneous Aza-Michael Addition Reaction by the Copper-Based Metal–Organic Framework (CuBTC)

Abstract

The copper benzene-1, 3, 5-tricarboxylate metal–organic framework (CuBTC) was found to be an effective heterogeneous catalyst for the aza-Michael addition reaction of the four types of amines to electron deficient alkenes at room temperature. The catalytic protocol showed high product yields and outstanding chemo selectivity. The cyclic amines (piperidine and pyrrolidine) and aliphatic amines (n-dibutylamine) provided aza-Michael addition with a high yield of product (⁓98%) within shorter reaction period (2 h) at room temperature under mild reaction conditions using CuBTC. However, it was observed that the aza-Michael reaction proceeded more slowly, giving 62% yield of product after 24 h in the case of aromatic amine (aniline) with n-butyl acrylate in the presence of CuBTC under identical reaction conditions. The catalyst could be reused four recycles without losing its initial catalytic activity and selectivity. XRD and SEM analysis further confirmed that the crystallinity of catalyst was retained during the reaction. A reaction mechanism is proposed for the aza-Michael addition reaction over heterogeneous CuBTC catalyst.