Porphyrin-Metalation-Mediated Tuning of Photoredox Catalytic Properties in Metal–Organic Frameworks

Photoredox catalytic activation of
organic molecules via single-electron
transfer processes has proven to be a mild and efficient synthetic
methodology. However, the heavy reliance on expensive ruthenium and
iridium complexes limits their applications for scale-up synthesis.
To this end, photoactive metal–organic frameworks (MOFs) exhibit
unique advantages as novel heterogeneous photocatalytic systems, yet
their utilization toward organic transformations has been limited.
Here we describe the preparation and synthetic applications of four
isostructural porphyrinic MOFs, namely, UNLPF-10a, -10b, -11, and
-12, which are composed of free base, InIII-, SnIVCl2-, and SnIV-porphyrin building blocks, respectively.
We demonstrate that the metalation with high valent metal cations
(InIII and SnIV) significantly modifies the
electronic structure of porphyrin macrocycle and provides a highly
oxidative photoexcited state that can undergo efficient reductive
quenching processes to facilitate organic reactions. In particular,
UNLPF-12 exhibits both outstanding photostability and efficient photocatalytic
activities toward a range of important organic transformations including
aerobic hydroxylation of arylboronic acids, amine coupling, and the
Mannich reaction.