Few-Layered Metal–Organic Framework Nanosheets as Catalysts for the Synthesis of 2,3-Dihydroquinazolinone and Propargylamines

Two-dimensional ultrathin metal–organic framework nanosheets (2D-MONs), obtained by reducing one dimension of metal–organic frameworks (MOFs) to a single or few layers with a sheet-like morphology, have recently received a great deal of attention in the field of catalysis owing to their porous structure, faster diffusion, and huge number of exposing active sites. In this work, a layered MOF has been prepared by treating 4-carboxyphenylboronic acid and imidazole as ligand precursors with the presence of Cu(OAc)2 through a one-pot in situ ligand synthesis strategy. The resulting bulk-layered MOF has been readily exfoliated into 2D-MONs with a thickness of 1.3 nm (2 layers) via ultrasonic liquid exfoliation. Featuring distinct CuII catalytic active sites in the frameworks, both the mother MOF and the resultant MONs are proven to be efficient and recyclable heterogeneous catalysts for the synthesis of 2,3-dihyroquinazolinones and propargylamines. Compared with the bulk MOF, the catalytic efficiency of the 2D-MONs can be obviously improved, especially for some bulky substrates, enabling MONs to outperform the bulk counterparts. Our work therefore provides a simple and straightforward way for the design and synthesis of MOFs and ultrathin 2D-MONs for heterogeneous catalysis in organic syntheses starting from simple and inexpensive precursors at the molecular level.