Transformation
of CO2 into valuable chemicals and especially
fuels is deemed as a promising approach to reduce our dependence on
fossil fuels and to alleviate climate change. Carbazole-based porous
polymers bearing rhenium-metalated polypyridine functionalities were
constructed via simple oxidative coupling reaction. These porous polymers
are employed as heterogeneous supports for immobilization of catalytically
active rhenium complexes and furthermore provide high CO2 adsorption capabilities and light absorption abilities, i.e., photosensitizing
properties. Consequently, such rhenium-metalated microporous polycarbazole
networks show high efficiencies for CO2 photoreduction
upon visible-light irradiation, with a CO evolution rate up to 623
μmol g–1 h–1 and selectivity
of 97.8%. The microporous solid photocatalyst shows enhanced stability
and photocatalytic performance compared to the molecular catalysts
during long-term use.
Multicomponent reactions (MCRs) can be used to introduce different functionalities into highly stable covalent organic frameworks (COFs). In this work, the irreversible three-component Doebner reaction is utilized to synthesize four chemically stable quinoline-4-carboxylic acid DMCR-COFs (DMCR-1−3 and DMCR-1NH) equipped with an acid−base bifunctionality. These DMCR-COFs show superior photocatalytic H 2 O 2 evolution (one of the most important industrial oxidants) compared to the imine COF analogue (Imine-1). This is achieved with sacrificial oxidants but also in pure water and under an oxygen or air atmosphere. Furthermore, the DMCR-COFs show high photostability, durability, and recyclability. MCR-COFs thus provide a viable materials' platform for solar to chemical energy conversion.
We demonstrate that several visible-light-mediated carbonÀ heteroatom cross-coupling reactions can be carried out using a photoactive Ni II precatalyst that forms in situ from a nickel salt and a bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl 2 ). The activation of this precatalyst towards cross-coupling reactions follows a hitherto undisclosed mechanism that is different from previously reported light-responsive nickel complexes that undergo metalto-ligand charge transfer. Theoretical and spectroscopic investigations revealed that irradiation of Ni(Czbpy)Cl 2 with visible light causes an initial intraligand charge transfer event that triggers productive catalysis. Ligand polymerization affords a porous, recyclable organic polymer for heterogeneous nickel catalysis of cross-coupling reactions. The heterogeneous catalyst shows stable performance in a packed-bed flow reactor during a week of continuous operation.
Covalent triazine
frameworks are an emerging material class that
have shown promising performance for a range of applications. In this
work, we report on a metal-assisted and solvent-mediated reaction
between calcium carbide and cyanuric chloride, as cheap and commercially
available precursors, to synthesize two-dimensional triazine structures
(2DTSs). The reaction between the solvent, dimethylformamide, and
cyanuric chloride was promoted by calcium carbide and resulted in
dimethylamino-s-triazine intermediates, which in
turn undergo nucleophilic substitutions. This reaction was directed
into two dimensions by calcium ions derived from calcium carbide and
induced the formation of 2DTSs. The role of calcium ions to direct
the two-dimensionality of the final structure was simulated using
DFT and further proven by synthesizing molecular intermediates. The
water content of the reaction medium was found to be a crucial factor
that affected the structure of the products dramatically. While 2DTSs
were obtained under anhydrous conditions, a mixture of graphitic material/2DTSs
or only graphitic material (GM) was obtained in aqueous solutions.
Due to the straightforward and gram-scale synthesis of 2DTSs, as well
as their photothermal and photodynamic properties, they are promising
materials for a wide range of future applications, including bacteria
and virus incapacitation.
We demonstrate that several visible-light-mediated carbonÀ heteroatom cross-coupling reactions can be carried out using a photoactive Ni II precatalyst that forms in situ from a nickel salt and a bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl 2 ). The activation of this precatalyst towards cross-coupling reactions follows a hitherto undisclosed mechanism that is different from previously reported light-responsive nickel complexes that undergo metalto-ligand charge transfer. Theoretical and spectroscopic investigations revealed that irradiation of Ni(Czbpy)Cl 2 with visible light causes an initial intraligand charge transfer event that triggers productive catalysis. Ligand polymerization affords a porous, recyclable organic polymer for heterogeneous nickel catalysis of cross-coupling reactions. The heterogeneous catalyst shows stable performance in a packed-bed flow reactor during a week of continuous operation.
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