Covalent organic frameworks (COFs) serve as good heterogeneous ligands and show promise for CO2 capture due to their persistent porosity, high surface area, fine thermal stability, and adjustable pore size. This paper describes a strategy for manufacturing tetramic and tetronic acids that makes use of a silver-based COF, Ag@TpDa, as a highly efficient and recyclable heterogeneous catalyst. There has been a spike of interest in employing metal-loaded covalent organic frameworks as reusable catalysts for the synthesis of important organic compounds in recent years. The catalytic efficiency of Ag@TpDa is investigated in the selective synthesis of tetramic and tetronic acids in the presence of 1 atm of CO2 using unsaturated amines and alcohols as starting substrates. By integration of CO2 into a varied variety of unsaturated amines and alcohols, the procedure provides moderate to high isolated amounts of tetramic and tetronic acids via the application of a singular catalyst. Notably, Ag@TpDa maintains consistent catalytic capability after six cycles, making it recoverable and reusable. A thorough theoretical research and accompanying tests are being conducted to determine the source of the catalyst's remarkable selectivity.

Carboxylation of amines is an important route to obtain amino acids. Herein, we have reported the synthesis and characterizations of a new COF/gC(3)N(4) composite which acted as a heterogeneous photocatalyst for the carboxylation of unprotected indoles and N-Boc-benzyl amines. We have used SnO2 nanoparticles as the cocatalyst and CO2 as the carbon source under visible light irradiation. This gave a range of carboxylated products both with unprotected indoles and N-Boc-benzylamines with high yield. Control experiments gave the optimum reaction conditions for this photocatalytic carboxylation. Light dependency of this reaction was confirmed by altering the intensity of light. Here, we have synthesized two different catalysts, TpBpy and Tz COF, and the gC(3)N(4) heterojunction which showed excellent photocatalytic activity. The photocatalysts, COF/gC(3)N(4), are recyclable and reusable for several cycles without a significant loss in performance. The synthesis of a drug compound Clopidogrel and drug formation unit Tirofiban is demonstrated with these photocatalytic protocols.

An efficient heterogeneous copper-loaded catalytic system for photocatalytic hydrogen evolution and reduction of CO2 to methanol has been reported. For the present photocatalytic reaction, an elegant strategy has been developed to heterogenize the homogeneously active copper-based catalysts via immobilization on the porphyrin-based porous organic polymer (namely, TpTph or TpPOP). This heterogeneous system acts as a very effective catalyst for visible-light-triggered hydrogen production (a high hydrogen production yield of about 598 mu mol) and selective CO2 reduction to methanol (a high yield of about 1.8 mol/gcat upon exposure to 15 W white light-emitting diode) under sustainable conditions (room temperature, atmospheric pressure, cocatalyst-free). Notably, Cu@TpPOP offers much easier recyclability than the homogeneous one. Further, the detailed theoretical (DFT) and experimental studies unravel mechanistic pathways to convergent photocatalytic hydrogen evolution and selective photoreduction of CO2 under ambient conditions.

Anthropogenic climate change drastically affects our planet, with CO2 being the most critical gaseous driver. Despite the existing carbon dioxide capture and transformation, there is much need for innovative carbon dioxide hydrogenation catalysts with excellent selectivity. Here, we present a fast, effective, and sustainable route for coupling diverse alcohols, amines and amides with CO2 via heterogenization of a natural metal-based homogeneous catalyst through decorating on functionalized graphene oxide (GO). Combined synthetic, experimental, and theoretical studies unravel mechanistic routes to convergent 4-electron reduction of CO2 under mild conditions. We successfully replace the toxic and expensive ruthenium species with inexpensive, ubiquitously available and recyclable iron. This iron-based functionalized graphene oxide (denoted as Fe@GO-EDA, where EDA represents ethylenediamine) functions as an efficient catalyst for the selective conversion of CO2 into a formaldehyde oxidation level, thus opening the door for interesting molecular structures using CO2 as a C1 source. Overall, this work describes an intriguing heterogeneous platform for the selective synthesis of valuable methylene-bridged compounds via 4-electron reduction of CO2.

A simple porous polymer framework (PPF) as a promising heterogeneous ligand for the Pd-catalyzed CO2 fixation reaction into diverse cyclic carbonates is reported. Several terminal epoxides and more challenging disubstituted epoxides were efficiently converted into value-added cyclic carbonates with satisfactory to excellent yields (i.e., 65 to 99% yields) and excellent selectivities (>99%) using an imine-linked Pd-based PPF catalytic system (namely, Pd@3D PPF) as an efficient catalyst and tetrabutylammonium bromide (TBAB) as a co-catalyst under mild conditions (1 atm CO2 pressure and room-temperature) without employing any solvents. Notably, the Pd-loaded PPF catalyst can be separated and reused over five times without significant loss of catalytic performance and selectivity for the cycloaddition of CO2 to epoxides. This intuitively appealing methodology tolerates a wide variety of functional groups and opens an avenue for Pd-based imine-linked frameworks as a reliable platform to control regioselectivity.

A 2D polyimide-linked covalent organic framework (COF) with band gap energy of 2.2 eV is developed as a stable and efficient porous photocatalyst which shows CO2 reduction to formic acid, formaldehyde and methanol.

Porous polymeric frameworks have received great interest over the past few years because of their nonstop growth as crystalline porous polymeric materials connected through covalent bonds and versatile utilities in diverse fields. The production of high-value organic compounds via sustainable and environment-friendly methods is an uphill struggle for researchers. The elegant strategy of using carbon dioxide as a C1 building block is an intriguing platform owing to its non-toxicity, easy accessibility, natural abundance, recyclability, non-flammability, and cheapness. Additionally, CO2 levels are regarded as the main contributor to the greenhouse effect (the most abundant greenhouse gas across the globe) and the aforementioned strategy needs to mitigate CO2 emissions. This present study describes the synthesis of silver nanoparticles (AgNPs) embedded in a porous polymeric framework, a reusable heterogeneous catalyst (recyclable over 5 times), TpMA (MC)@Ag. The synthesized catalyst is characterized by using FT-IR, PXRD, XPS, FE-SEM, TEM, EDAX, TGA DTA, and N2 sorption studies. Additionally, the catalysts can be easily recycled to generate the desired α-alkylidene cyclic carbonates and oxazolidinone compounds under solvent-free conditions. This research demonstrates the potential of nanoporous 2D porous polymeric framework-based materials in the area of catalysis, specially, in CO2 capture and chemical fixation. These findings offer a promising approach for the chemical fixation of CO2 into α-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols utilizing AgNPs embedded in a 2D catalyst, which functions as a potential heterogeneous catalyst under mild conditions (e.g., solvent-free approach).

Sustainable metal-free catalytic conversion of carbon dioxide (CO2) via cycloaddition of epoxides with CO2 has shown great promise but suffers from a lack of recyclability because of the homogeneous nature, limiting their use. Heterogeneous organocatalysts have gained immense attention in the last decade because of superior application potential and their important characteristics, and they also play pivotal roles in making environmentally friendly processes a reality. Herein, we describe an unprecedented postsynthetic modification approach for efficient covalent immobilization of quaternary ammonium salts to a microporous covalent organic framework (COF). More interestingly, no noticeable loss in crystallinity occurred after postsynthetic modification (PSM) and the quaternary ammonium salt-decorated COF (MA-PDA IL@COF) consists of only micropores (around 6-15 A), which are smaller than most of the reported COF-based catalysts. Detailed investigations on CO2 chemical fixation reveal that ionic liquid-based COF is a promising metal-free catalyst to promote the coupling of CO2 with epoxides under very mild conditions (metal-free/solvent-free/cocatalyst-free/additive-free and 1 atm of CO2 pressure). The metal-free COF displayed quantitative selectivity, and more intriguingly, the cycloaddition reaction with CO2 occurred with a high efficiency, broad scope, and functional group tolerance without additives or cocatalysts. The catalytic system can be recovered for repeated use at least five times with almost similar catalytic performance and a promising prerequisite for industrial implementation.

Porous organic polymers (POPs) have attracted substantial attentions over the years due to their exceptionally high specific surface areas, high chemical stability of the organic network and ease of surface functionalization with the desired organic groups. In this work, a triazine based POP (TrzPOP) was synthesized through Schiff base polycondensation reaction between a tetramine bearing triazine rings and phenolic-OH group rich dialdehyde. Ni nanoparticles (NiNP) synthesized independently were immobilized over TrzPOP to obtain the NiNP@TrzPOP composite catalyst. This TrzPOP possesses a high BET surface area of 1494 m(2) g(-1) and low band gap, which facilitates its role as visible light absorbent. NiNP@TrzPOP with N-rich surfaces and phenolic-OH moieties displayed excellent photocatalytic activity in the CO2 photoreduction under mild reaction conditions. NiNP@TrzPOP composite selectively reduces CO2 to methanol. The turn over number (TON) for this photoreduction of CO2 under optimized reaction conditions is 270, which is considerably high comparing to other reported photocatalytic systems. Moreover, NiNP@TrzPOP composite catalytic system showed high recycling efficiency without noticeable decrease in its performance over five consecutive reaction cycles, suggesting its huge potential for large-scale methanol synthesis from the renewable carbon source.

Direct photochemical carboxylation of C(sp(3))-H bonds with CO2 is an uphill task and it has attracted increasing attention. In the present study, we report an elegant strategy for visible-light-triggered C(sp(3))-H carboxylation of amines with CO2 into a-amino acids using a stable crystalline polyimide-based covalent organic framework (PI-COF) as an efficient heterogeneous photocatalyst and NiO nanoparticles (NiO NPs) as a cocatalyst under ambient conditions (room temperature and atmospheric CO2 pressure). Diverse amino acids are produced in moderate-to-high yields. This methodology tolerates a range of functional groups and displays remarkable regioselectivity. Various drugs were effectively achieved using this light-assisted approach. The high chemical stability of the COF and its strong interactions with NiO NPs renders the catalytic system to be highly recyclable (i.e., over five times). More interestingly, this photoinduced carboxylation reaction occurred without the involvement of any sacrificial electron donors. Based on computational (DFT) investigations, a tentative mechanism revealed the formation of CO2 radical anion at the conduction band (CB) of the COF via single electron transfer mediated by NiO nanoparticles which combined with amine radical cation at the valence band of the COF to form a-amino acid.

A 2D covalent organic framework (COF) was synthesized by copolymerization between 4,4′-biphenyldicarbaldehyde and 1,3,5-tris-(4-aminophenyl) triazine (TAPT). This COF exhibited excellent photocatalytic performance for the CO 2 reduction to methanol.

A simple covalent organic framework (COF) bearing β-ketoenamine units as a potential heterogeneous ligand for ZnII-catalyzed fixation and transformation of CO2 into value-added chemicals is reported. Catalytic investigations convincingly demonstrated that the ZnII-functionalized covalent organic framework (Zn@TpTta) exhibits perfect catalytic activity in the fixation of CO2 for diverse epoxides with various substituents under sustainable conditions. A variety of terminal epoxides and slightly more complicated disubstituted epoxides were transformed into the corresponding cyclic carbonates with satisfactory to excellent yields (i.e., 69 to 99% yield) upon exposure to CO2 (1 atm) under solvent-free conditions (sustainable approach). On the other hand, this ZnII-loaded covalent organic framework also displayed excellent performance in facilitating atmospheric cyclizative CO2 capture, which led to the formation of diverse cyclic carbamates (i.e., 61 to 94% yield) from unsaturated amine systems using N-iodosuccinimide (NIS) as an iodinating agent and PEG-400 as a biodegradable and green polymeric solvent under base-free conditions (sustainable approach). The newly synthesized COF-based catalyst, namely, Zn@TpTta, has been completely characterized by SEM (scanning electron microscopy), EDX (energy dispersive X-ray analysis), HRTEM (high-resolution transmission electron microscopy), BET (Brunauer-Emmett-Teller), PXRD (powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), ICP (inductively coupled plasma), etc. More intriguingly, the catalytic system could be recycled over five times without a noticeable loss of catalytic performance for both reactions. This study opens an avenue for the Zn(II) embedded COF as a promising platform for regulating regioselectivity.

Photocatalytic metal-free carboxylation of olefins offers an environment-friendly approach for resolving the increasing energy issue as well as mitigating the dilemma caused by the greenhouse effect. Carboxylation of styrene and its derivatives by photocatalytic CO2 reduction reaction shows great potential for sustainable utilization of greenhouse gas CO2 into valuable chemicals. Herein, we have constructed a highly crystalline and thermally stable 2D porous covalent organic framework (COF) having very low band-gap energy, 1.8 eV and it shows efficient photocatalytic activity towards the carboxylation of aryl-alkenes in good yields in presence of p-terphenyl as a co-catalyst at ambient temperature under visible light irradiation and 1 atmospheric CO2 pressure which facilitates to overcome the current transition metal catalyzed approaches. In addition, TR-OT COF is a proficient and highly selective catalyst with outstanding recyclability. This suggests that this COF material is a novel photocatalyst for CO2 reduction towards it, alpha, beta-carboxylation of styrene and its derivatives under 20 W light-emitting diode (LED) light.

We have demonstrated the photo-catalytic fixation of CO2 over epoxides for the formation of corresponding cyclic carbonates using a mesoporous Covalent Organic Framework (COF) which acts as a potential photocatalyst with TBAB (Tetrabutyl ammonium bromide), 5 mol% as the co-catalyst under atmospheric pressure in visible light. Greater than 86% yield of the isolated product is achieved with the use of 5 mg of catalyst. The use of Catalyst and co-catalyst TBAB controls the reaction cycle. There is no progress of the reaction occurred in the absence of light (445 nm) even on the elevation of reaction temperature. We have also demonstrated that 25% of the isolated product could be obtained with the use of sunlight using the catalytic cycle. These results open the door to an entirely new class of protocol for photo catalytically fixation of CO2 into cyclic carbonate from epoxide using COF as photocatalyst under visible light.

Correction for ‘Flower-like AgNPs@m-MgO as an excellent catalyst for CO2 fixation and acylation reactions under ambient conditions’ by Arpita Hazra Chowdhury et al., New J. Chem., 2018, 42, 14194–14202, DOI: 10.1039/C8NJ02286K.

The photocatalytic carboxylation of aryl derivatives was demonstrated under CO2 at atmospheric pressure using a mesoporous covalent organic framework (COF) as the active photocatalyst with triethylamine (TEA) as a sacrificial electron source under visible light. A yield of greater than 91% of the isolated product was achieved with 5 mg of catalyst. The reaction cycle is dependent on the use of the Ni(dmg)(2) co-catalyst and the sacrificial electron donor (TEA). The reaction does not occur in the absence of light (445 nm) even at elevated reaction temperature. We have also demonstrated that a yield of 32% of the isolated product could be obtained with the use of sunlight in the catalytic cycle. Additionally, this heterogeneous catalytic system was recyclable and reusable for several cycles.

Covalent organic frameworks (COFs) have been gaining substantial attention over the past decade due to their developing crystalline porous polymeric nature linked by strong covalent bonds and widespread applications in various fields. Currently, three-dimensional COFs (3D COFs) are engaging the spotlight due to their distinctive porous features, greater surface area, and exceptional performances in comparison with formerly published two-dimensional (2D) frameworks with the AA-stacking layered mode. In this paper, we present, for the first time, a nanoporous 3D-COF-based zinc(II) catalyst (Zn@RIO-1), which shows an efficient pathway for the chemical conversion of carbon dioxide to produce alpha-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols. The microporous material with a high surface area (312.61 m(2)/g) facilitates both types of catalytic reactions under atmospheric CO2 pressure. More importantly, easily recyclable and reusable catalysts produced moderate to high yields of desired carbonates as well as oxazolidinone products under solvent-free conditions. This study emphasizes the capability of nanoporous 3D-COF-based material in the catalysis field, more specifically in the field of CO2 capture and chemical fixation to fine chemicals. These results pave a spectacular pathway for the chemical fixation of CO2 into a-alkylidene cyclic carbonates and oxazolidinones from propargylic alcohols using 3D-COF as a potential heterogeneous ligand under sustainable conditions (i.e., solvent-free).

The present work introduces the favorable synthesis of porous functionalized nanomaterials with excellent surface area, porosity, and high CO2 capture ability to facilitate cyclizative reactions by incorporating the CO2 molecule into highly reactive organic moieties. We have attempted to fulfill the target by the decoration of Ag NPs over the exterior surfaces of covalent organic frameworks (COFs) TpPa-1 and TpTta to achieve Ag@TpPa-1 and Ag@TpTta nanomaterials with an absolutely ordered structure. Characterizations of the nanocatalysts (Ag@TpPa-1 and Agp TpTta) have been performed by field emission scanning electron microscopy, thermogravimetric tools, N-2 adsorption/desorption, transmission electron microscopy, Fourier transform infrared spectroscopy, UV-vis, and powder X-ray diffraction analysis. These Ag NPs architectured porous COFs described excellent performance for the benign synthesis of cyclic carbamates from unsaturated amines in the presence of N-iodosuccinimide (NIS) and several 2-oxazolidinone derivatives from propargylamine derivatives via cyclizative atmospheric CO2 capture under solvent-free and alkali-free conditions (sustainable approach). The microporous material Ag@TpTta revealed most excellent catalytic performance than Ag@TpPa-1 during production of cyclic carbamates and oxazolidinones which indicates that the selection of Ag NPs decorated COFs with the excellent surface area has a contributory effect on carboxylative cyclization reaction. Density functional theory studies furnished important information to establish the detailed mechanism of silver (0) catalyzed CO2 incorporation into unsaturated amine. These COFs enriched with N centers can interact with the Ag NPs at their outer exterior surfaces very tightly. These two nanocatalysts exhibited magnificent recycling efficiencies for the generation of cyclic carbamates and 2-oxazolidinones with almost zero silver leaching from the exterior part of the catalyst.

The present study describes the favourable construction of a crystalline covalent organic framework (COF) with exceptional surface area, tunable pore size and huge CO2 capture efficiency to facilitate a novel multicomponent cyclization by introducing CO2 into extremely reactive organic skeletons. In the presence of a catalytic Cu/CuxOy NP-loaded COF, several 2-bromo-3-alkylacrylic acids combined with several amine derivatives and CO2 (0.1 MPa) are converted to the desired oxazolidinediones in excellent yields (up to 96%) under alkali-free conditions and ambient temperature.