This review discusses recent advances in the photocatalytic carboxylation of C(sp3)–X (X = H, N) bonds, C(sp2)–X (X = H, N, (pseudo)halide) bonds and C(sp)–H bonds with CO2.
A rhenium–pyrene catalyst that dramatically promotes sunlight-induced CO2RR efficiency was developed by enhancing intermolecular electron transfer efficiency and visible light-harvesting ability.
Visible
light-induced photocatalytic CO2 reduction reaction
(CO2RR) is a feasible and promising option to tackle the
greenhouse effect and energy crisis. Herein, two ferric porphyrin-based
porous organic polymer semiconductors, hereafter referred to as POPn-Fe (porous organic polymers, n = 1 or
2, corresponding to a benzene/biphenyl unit as a linker between porphyrin
units), are synthesized for the visible light-driven CO2RR to produce syngas. The CO/H2 evolution rates for POP2-Fe
under irradiation >420 nm are found to successfully reach up to
3043
and 3753 μmol g–1 h–1, respectively.
Interestingly, the experiment results imply that the ferric porphyrin
site could be responsible for CO evolution and the uncoordinated porphyrin
unit in POPn or POPn-Fe semiconductors
may be obligate for H2 formation. Furthermore, as evidenced
by Mott–Schottky plots, the extended π-conjugation with
the biphenyl linker makes POP2-Fe a lower conduction band potential,
which helps the ferric porphyrin sites capture electrons from the
photosensitizer, thus producing more CO to realize selectivity control.
Also, the efficient catalytic activity of POP2-Fe is presumably attributed
to the accelerated charge transfer as well as facilitates photogenerated
electron and hole separation. This work offers an elegant strategy
to design and optimize earth-abundant metal visible light photocatalysis
for CO2 reduction to syngas with CO/H2 ratio
control.
An efficient and regioselective remote C(5)-H nitration of 8-aminoquinoline amides by using the economical and nontoxic Fe(NO)·9HO as promoter and nitro source has been developed. Furthermore, when CuCl·2HO was used as a catalyst, 8-aminoquinoline amides dominantly underwent bisnitration to give 5,7-dinitro-8-aminoquinoline amides. Notably, this is the first example in which Fe(NO)·9HO plays a dual role as both chelating promoter and nitration reagent, and CuCl·2HO acts as an efficient catalyst for the bisnitration of quinolines.
Superbase-derived
task-specific ionic liquids (STSILs) represent
one of the most attractive and extensively studied systems in carbon
capture via chemisorption, in which the obtained CO2 uptake
capacity has a strong relationship with the basicity of the anions.
High energy input in desorption and side reactions caused by the strong
basicity of the anions are still unsolved issues. The development
of other customized STSILs leveraging an alternative driving force
to achieve efficient CO2 chemisorption/desorption is highly
desirable yet challenging. In this work, carbanion-derived STSILs
were developed for efficient CO2 chemisorption via a carboxylic
acid formation pathway. The STSIL with the deprotonated malononitrile
molecule ([MN]) as the anion exhibited much higher CO2 uptake
capacity than the one derived from 2-methylmalononitrile ([MMN]).
Notably, this trend was opposite to their basicity ([MN] < [MMN]).
Detailed characterization of the products, supported by density functional
theory simulations of spectra and calculations of the reaction energetics,
demonstrated that carboxylic acid was formed upon reacting with CO2 via proton transfer in [MN]-derived STSILs but not in the
case of [MMN] due to lack of an α-H. The preference of the carboxylic
acid product over carboxylate formation was driven by the extended
conjugation among the central sp2 carbon, the as-formed
carboxylic acid, and the two nitrile groups. The achievements made
in this work provide an alternative design principle of STSILs by
leveraging the extended conjugation in the CO2-integrated
product.
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