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.