Framework-Topology-Dependent Catalytic Activity of Zirconium-Based (Porphinato)zinc(II) MOFs

Catalytic activity
for acyl transfer from N-acetylimidazole
(NAI) to different pyridylcarbinol (PC) regioisomers (2-PC, 3-PC,
and 4-PC) is demonstrated for a set of topologically diverse, zirconium-based
(porphinato)zinc metal–organic frameworks (MOFs). The MOFs
studied are PCN-222, MOF-525, and NU-902, which are based on the csq, ftw, and scu topologies, respectively. The experimentally
obtained reaction kinetics are discussed in light of molecular modeling
results. The catalytic activity is shown to vary across the series
of MOFs due to the different extent to which each topology facilitates
reactant preconcentration and alignment of PC and NAI via coordination
to framework porphyrin sites (orientation effects). Trends of experimental
initial reaction rates with MOF topology and PC regioisomer are consistent
with preconcentration effects, which depend on the number of porphyrin
sites per volume of MOF, as well as with orientation effects, which
depend on the number of porphyrin pairs per volume of MOF that bind
PC and NAI in such a way that they are primed to form the required
transition state. The present work shows how the proper alignment
of catalytic linkers can enhance reaction rates in MOFs.