Charge
separation plays a crucial role in regulating photochemical
properties and therefore warrants consideration in designing photocatalysts.
Metal–organic frameworks (MOFs) are emerging as promising candidates
for heterogeneous photocatalysis due to their structural designability
and tunability of photon absorption. Herein, we report the design
of a pyrazole–benzothiadiazole–pyrazole organic molecule
bearing a donor–acceptor–donor conjugated π-system
for fast charge separation. Further attempts to integrate such a photosensitizer
into MOFs afford a more effective heterogeneous photocatalyst (JNU-204).
Under visible-light irradiation, three aerobic oxidation reactions
involving different oxygenation pathways were achieved on JNU-204.
Recycling experiments were conducted to demonstrate the stability
and reusability of JNU-204 as a robust heterogeneous photocatalyst.
Furthermore, we illustrate its applications in the facile synthesis
of pyrrolo[2,1-a]isoquinoline-containing heterocycles,
core skeletons of a family of marine natural products. JNU-204 is
an exemplary MOF platform with good photon absorption, suitable band
gap, fast charge separation, and extraordinary chemical stability
for proceeding with aerobic oxidation reactions under visible-light
irradiation.
Radical borylation using N‐heterocyclic carbene (NHC)‐BH3 complexes as boryl radical precursors has emerged as an important synthetic tool for organoboron assembly. However, the majority of reported methods are limited to reaction modes involving carbo‐ and/or hydroboration of specific alkenes and alkynes. Moreover, the generation of NHC‐boryl radicals relies principally on hydrogen atom abstraction with the aid of radical initiators. A distinct radical generation method is reported, as well as the reaction pathways of NHC‐boryl radicals enabled by photoredox catalysis. NHC‐boryl radicals are generated via a single‐electron oxidation and subsequently undergo cross‐coupling with the in‐situ‐generated radical anions to yield gem‐difluoroallylboronates. A photoredox‐catalyzed radical arylboration reaction of alkenes was achieved using cyanoarenes as arylating components from which elaborated organoborons were accessed. Mechanistic studies verified the oxidative formation of NHC‐boryl radicals through a single‐electron‐transfer pathway.
Multicomponent
metal–organic frameworks (MOFs) have received
an increasing amount of attention due to their potential to produce
new topologies, pore metrics, and functionalities compared to MOFs
with a single metal cluster and one organic linker. Herein, five isoreticular
Zn MOFs were obtained by mixing two types of linear ditopic linkers
in a one-pot solvothermal synthesis. Interestingly, in the resulting
Zn MOFs a six-connected cyclic trinuclear Zn(II) cluster and an eight-connected
linear trinuclear Zn(II) cluster coexist, leading to an uncommon (6,8)-connected
network. Catalytic activities toward the solvent-free Knoevenagel
reactions were observed for all of these MOFs. Further experimental
and computational studies suggest that they are Brønsted acid–base
bifunctional catalysts. Through chemical modifications of dicarboxylate
ligands, including their aromatic backbones and substituents, we have
successfully implemented reticular chemistry for the modulations of
pore sizes, surface areas, and catalytic performances in a series
of four-component isoreticular MOFs.
An unprecedented application of trifluoromethanesulfonyl hydrazides as trifluoromethylating agents has been demonstrated in two vicinal difunctionalization reactions of terminal alkenes: the copper-catalyzed three-component vicinal chlorotrifluoromethylation of arylakenes with TfNHNHBoc and NaCl and the tandem trifluoromethylation/cyclization of N-arylacrylamides with TfNHNHBoc. The reactions proceeded in the presence of inexpensive oxidants under mild conditions and provided a range of structurally diverse trifluoromethyl-containing compounds with high regioselectivity.
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