Acid Catalysis in Confined Channels of Metal–Organic Frameworks: Boosting Orthoformate Hydrolysis in Basic Solutions

Enzymes
use a confined docking cavity and residual groups in the
cavity to regulate substrate selectivity and catalytic activity. By
mimicking enzymes, we herein report that metal–organic framework
(MOF) KLASCC-1, with channels and inside-channel
pyridyl groups, can promote orthoformate hydrolysis in basic solutions.
By studying pH-dependent hydrolysis and using an analogue MOF that
lacks inside-channel pyridyl groups, we proved protonated pyridyl
groups as acid catalytic sites for orthoformate hydrolysis. By using
MOFs with only open pyridyl groups, we demonstrated the necessity
of the confined channels. X-ray diffraction structures of KLASCC-1 with encapsulated substrates confirmed that these
channels can regulate activity and size selectivity. Recycling tests
and crystallographic studies confirmed that KLASCC-1 kept its framework structure in catalysis. This work shows
the potentials of using MOFs for host–guest catalysis that
cannot be otherwise completed and underlines the advantages of using
crystal engineering to identify active sites.