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The Friedel–Crafts alkylation strategy was used to prepare a hypercrosslinked polymer catalyst, which showed superior performance towards the cycloaddition reaction of CO2 with epoxides.

Porous materials with heterogeneous nature occupy a pivotal position in the chemical industry. This work described a facile pre- and post-synthetic approach to modify porous hypercrosslinked polymer with quaternary ammonium bromide, rendering it as efficient catalyst for CO2 conversion. The as-prepared porous ionic polymer (PiP@QA) displayed an improved specific surface area of 301 m2·g−1 with hierarchically porous structure, good selective adsorption of CO2, as well as high ion density. Accordingly, PiP@QA catalyst exhibited excellent catalytic performances for the solvent-free synthesis of various formamides from CO2, amines and phenylsilane under 35 °C and 0.5 MPa. We speculated that the superior catalytic efficiency and broad substrate scope of this catalyst could be resulted from the synergistic effect of flexible ionic sites with unique nanoporous channel that might increase the collision probability of reactants and active sites as well as enhance the diffusion of reactants and products during the reaction process. With the good reusability, PiP@QA was also available for the efficient conversion of simulated flue gas (15% CO2 in N2, v/v) into target formamides with quantitative selectivity at room temperature, which further highlighted its industrial application potential in chemical recycling the real-word CO2 to valuable products.

Catalytic oxidative dehydrogenation (ODH) of N-heterocycles has been considered to be an important transformation to access the corresponding nitrogen-containing heteroarenes. Herein, we developed porphyrin-based and imidazole-linked conjugated microporous polymers by metal-free catalytic condensation of a carboxyl porphyrin and phenylic diamine in polyphosphoric acid medium. The two synthesized polymers, TCPP-TAB and TCPP-HATP, exhibit a broad visible light response, high surface area and suitable redox potentials that are tunable. As expected, TCPP-TAB and TCPP-HATP as metal-free photocatalysts exhibit excellent photocatalytic performance and good substitution tolerance in ODH reactions of various N-heterocycles including tetrahydroisoquinolines, tetrahydroquinolines and indolines under base- and additive-free conditions with ambient air at room temperature. More importantly, heterogeneous TCPP-TAB and TCPP-HATP can be reused at least five times and ten times without obvious loss of catalytic activity, respectively, which is possibly attributed to their ultrastable cyclic imidazole joints. The current work provides a metal-free, efficient, green, and reproducible approach to perform ODH reactions of N-heterocycles under mild conditions.

In this work, a mild and sustainable catalytic aerobic epoxidation of alkenes catalyzed by cobalt porphyrin was performed in the presence of sunflower seeds oil. Under ambient conditions, the conversion rate of trans-stilbene reached 99%, and selectivity toward epoxide formation was 88%. The kinetic studies showed that the aerobic epoxidation followed the Michaelis–Menten kinetics. Mass spectroscopy and in situ electron spin resonance indicated that linoleic acid was converted to fatty aldehydes via hydroperoxide intermediates. A plausible mechanism of epoxidation of alkenes was accordingly proposed.

A tubular MOF with adequate active sites is prepared by the bending of metal-coordinated honeycombed frameworks via titration and shows fast catalytic kinetics with lower catalytic loading for CO2 conversion. The TON is observed to be 2300 and the corresponding TOF of up to 173 h-1 is achieved for the first time.

Quaternary phosphine type hypercrosslinked polymer catalysts were successfully prepared using the Friedel-Crafts alkylation reactions, which benefit from the synergistic effects between the Brønsted acidity of the hydroxyl group and nucleophilicity of the Br

Diamine-decorated graphene oxide (NH2-GO) is successfully synthesized by covalently intercalated ethanediamines into the flat planes and edge of the GO sheet. The diamines could be act as buffer layer, thereby avoiding the stacking of graphene sheets, and offer abundant metal-chelating sites to subsequently obtain well-dispersed metal nanoparticles of small size. After the in situ reduction and deposition of AuNPs, it was found that the Au particle size of Au0.9%@NH2-GO estimated to be around 2–5 nm. The as-prepared GO-supported small AuNPs exhibited good catalytic performance for the heterogeneous epoxidation of alkenes with H2O2 under mild conditions. Notably, they presented good expansibility for either bulky or less bulky alkenes in this reaction, owing to the facilitated efficiency of mass transfer of substrates and products resulted from the supporting effect of intercalated diamines and high surface area of GO. Moreover, these heterogeneous catalysts could be readily recovered and recycled for five times with the remained activity and selectivity. Gold nanoparticles of small size immobilized on the diamine-decorated graphene oxide has been developed, which employed as an efficient, universal and reusable catalyst for the epoxidation of alkenes using H2O2 as an oxidant.

An imidazolium-based ionic liquid (IL) functionalized zinc porphyrin catalyst was successfully synthesized for the first time, and was employed as an efficient catalyst for CO2 transformation including both the chemoselective synthesis of cyclic carbonates from various epoxides and the regioselective synthesis of 5-aryl-2-oxazolidinones from N-substituted aziridines. Detailed studies demonstrated that the intramolecular cooperative effect between the coordinated zinc center (electrophile) and flexible bromine anions (nucleophile) could mediate these reactions effectively under solvent-free and mild conditions. More importantly, the IL-based catalyst could be readily recovered by solvent precipitation and reused with retention of high activity and selectivity more than ten times based on the concept of “one-phase catalytic coupling with two-phase separation”.

On the basis of the development of function-oriented synthesis (FOS), we presented for the first time an efficient and one-pot construction of functional ionic polymers (FIPs) through the phenol–formaldehyde condensation process (pre-synthetic approach); FIPs had high density of Bronsted acidic and ionic sites. Considering the electrophilic–nucleophilic dual activation of phenolic hydroxyl groups and bromide anions, the imidazolium-based FIP-Im exhibited high activity for metal-, solvent- and additive-free synthesis of cyclic carbonates from CO2 and epoxides under mild conditions. Then, to obtain higher ionic density and a more flexible skeleton, FIP-Im@QA was also prepared by implanting quaternary ammonium (QA) in the framework of FIP-IMvia the Williamson ether synthesis (post-synthetic modification), which demonstrated high efficiency in the N-formylation reaction of multitudinous secondary amines with CO2 and PhSiH3 at ambient temperature. More interestingly, these function-oriented catalysts were compatible with the target transformation under low CO2 concentration (15% in 85% N2, v/v) and were also reused for more than six times without a significant loss of activity and selectivity. Therefore, this study could not only facilitate the design and construction of FIPs, but also provide sustainable protocols for efficient production of value-added chemicals from CO2 under mild conditions.

Multifunctionalization of organic polymers for acting synergistically on substrate is of wide interest in the field of modern catalysis, but it is still a significant challenge. Herein, two novel bifunctional polymers were first designed and synthesized by combining ionic liquids (ILs) with zinc(II) porphyrin through simple and reversible Schiff base reactions. The fabricated polymers with flexible structures and nitrogen-rich environments presented high affinity toward CO2 molecules at ambient conditions. Owing to the cooperative nature of intercalated ILs and Lewis acidic metal sites, these materials could serve as efficient heterogeneous catalysts for the insertion of CO2 into epoxides to produce cyclic carbonates. As expected, these polymers exhibited good catalytic performance, robust constancy, excellent recyclability, and good substrate expansibility for this reaction in the absence of cocatalyst under mild or even ambient conditions. Notably, the selected catalyst SYSU-Zn@IL2 could directly conver...

A facile and one-pot synthesis of metalloporphyrin-based ionic porous organic polymers (M-iPOPs) was performed through a typical Yamamoto-Ullmann coupling reaction for the first time. We used various characterization techniques to demonstrate that these strongly polar Al-based materials (Al-iPOP) possessed a relatively uniform microporosity, good swellable features, and a good CO2 capture capacity. If we consider the particular physicochemical properties, heterogeneous Al-iPOP, which bears both a metal active center and halogen anion, acted as a bifunctional catalyst for the solvent- and additive-free synthesis of cyclic carbonates from various epoxides and CO2 with an excellent activity and good recyclability under mild conditions. Interestingly, these CO2 -philic materials could catalyze the cycloaddition reaction smoothly by using simulated flue gas (15 % CO2 in N2 , v/v) as a raw material, which indicates that a stable local microenvironment and polymer swellability might promote the transformation. Thus, the introduction of polar ionic liquid units into metalloporphyrin-based porous materials is regarded as a promising new strategy for the chemical conversion of CO2 .

The chemical transformation of CO2 under mild conditions remains a great challenge because of its exceptional kinetic and thermodynamic stability. Two important reactions in the transformation of CO2 are the N-formylation reaction of amines using hydrosilanes and CO2, and the cycloaddition of CO2 to epoxides. Here, we report the high efficiency of bifunctional metallosalen complexes bearing quaternary phosphonium salts in catalyzing both of these reactions under solvent-free, mild conditions without the need for co-catalysts. The catalysts' bifunctionality is attributed to an intramolecular cooperative process between the metal center and the halogen anion. Depending on the reaction, this activates CO2 by permitting either the synergistic activation of Si–H bond via metal–hydrogen coordinative bond (M–H) or the dual activation of epoxide via metal–oxygen coordinative bond (M–O). The one-component catalysts are also shown to be easily recovered and reused five times without significant loss of activity or selectivity. The current results are combined with previous work in the area to propose the relevant reaction mechanisms.

A series of new metallosalen-based ionic porous organic polymers (POPs) were synthesized for the first time using a simple unique strategy based on the free-radical copolymerization reaction. Various techniques were used to characterize the physicochemical properties of these catalysts. These well-designed materials endowed high surface area, hierarchical porous structures, and enhanced CO2 /N2 adsorptive selectivity. Moreover, these POPs having both metal centers (Lewis acid) and ionic units (nucleophile) could serve as bifunctional catalysts in the catalytic conversion of CO2 into high value-added chemicals without any additional co-catalyst under mild and solvent-free conditions, for example, CO2 /epoxides cycloaddition and Nformylation of amines from CO2 and hydrosilanes. The results demonstrated that the irregular porous structure was very favorable for the diffusion of substrates and products, and the microporous structural property resulted in the enrichment of CO2 near the catalytic centers in the CO2 -involved transformations. Additionally, the superhydrophobic property could not only enhance the chemoselectivity of products but also promote the stability and recyclability of catalysts.

A series of metalloporphyrin-based hyper-crosslinked polymers (M-HCPs: M=Al, Co, Fe, Mn) has been directly synthesized through Friedel–Crafts alkylation reactions. The M-HCPs afforded abundant permanent nanopores, high Brunauer–Emmett–Teller (BET) surface area, and exceptional CO2/N2 adsorptive selectivity. The experimental results suggested that the hollow tubular Al-HCP exhibited extraordinary catalytic performance in the solvent-free synthesis of cyclic carbonates from epoxides and CO2 by using tetrabutylammonium bromide as a cocatalyst under mild conditions, which was clearly superior to the corresponding homogeneous analogue. Surprisingly, a high turnover frequency (TOF) value of 14 880 h−1 was achieved with propylene oxide at 100 °C and 3.0 MPa, which was a promising result for industrial production compared with previously reported heterogeneous catalysts. More interestingly, Al-HCP could smoothly catalyze the cycloaddition reaction, producing the corresponding cyclic carbonates by using simulated flue gas (15 % CO2 and 85 % N2 in volume) as the raw material under ambient conditions. Moreover, Al-HCP could be readily recycled and efficiently reused more than ten times, exhibiting excellent stability.

A sustainable method is developed for the selective and additive-free synthesis of imines from primary amines with TBHP catalyzed by bioinspired manganese complex (MnCl2(TPA)) at room temperature. Use of 0.2 mol % MnCl2(TPA) was efficient enough for this transformation by offering excellent conversions up to 98.2% along with 93.4% product yield within 1 h. The influence of reaction parameters (catalyst dosage, solvent, reaction temperature, time, etc.) on the catalytic performance was also investigated in detail. Building on these results, the selected MnCl2(TPA) was further employed to transform various primary amines into corresponding imines and exhibited good compatibility even for the challenging aliphatic amine. The high efficiency, combining with a large substrate scope and ambient reaction conditions, makes the developed bioinspired Mn complex/TBHP system a promising pathway to produce imines. This work also paves a way to the expansion of non-heme metal catalysts as efficient platforms for various oxidation reactions.

Multifunctionalization of porous organic polymers (POPs) for working in concert on a substrate is now a research topic in CO2 catalysis, yet it remains challenging. This work describes a pre- and post-synthetic strategy to design metalloporphyrin-based azo-hierarchical porous ionic polymers (ZnTPP/QA-azo-PiPs), which were synthesized based on diazo-coupling reaction of tetra(4-aminophenyl) porphyrin zinc with tri/diphenols in aqueous solution under mild conditions, followed by etherification with quaternary ammonium bromide. This synthetic approach endows ZnTPP/QA-azo-PiP1 with features of an improved surface area (181 m2/g), hierarchical porosity, and high-density active sites. ZnTPP/QA-azo-PiP1 presented a noteworthy CO2 uptake of 1.77 mmol/g at 273 K and 1.0 bar and good CO2/N2 selectivity of 44.8. As expected, ZnTPP/QA-azo-PiP1 showed quantitative conversion and selectivity for a range of epoxides under mild conditions (1.0 MPa, 80 °C, 12 h) in the CO2 cycloaddition reaction. ZnTPP/QA-azo-PiP1 could been recycled easily and retained complete retention of activity and selectivity for over 7 cycles. Moreover, with efficacious activity in conversion of diluted CO2 (15% CO2 in 85% N2, v/v), ZnTPP/QA-azo-PiP1 could smoothly catalyze CO2-involved reaction to produce oxazolidinones and N-formylated amines under mild conditions. This work promotes sustainable synthesis of advanced multifunctional POPs and gives great promise for their application in synthetic transformations of CO2.

A simple cooperative catalytic system was successfully developed for the solvent-free N-formylation of amines with CO2 and hydrosilanes under ambient conditions, which was composed of a Zn(salen) catalyst and quaternary ammonium salt. These commercially available binary components activated the Si-H bonds effectively, owing to the intermolecular synergistic effect between Lewis base and transition metal center (LB-TM), and subsequently facilitated the insertion of CO2 to form the active silyl formats, thereby leading to excellent catalytic performance at a low catalyst loading. Furthermore, the bifunctional Zn(salen) complexes, with two imidazolium-based ionic-liquid (IL) units at the 3,3'-position of salen ligand, acted as intramolecularly cooperative catalysts, and the solvent-regulated separation resulted in facile catalyst recycling and reuse.

A set of heteropolyacid-based ionic heterogeneous catalysts (PW@IL-GO(m)) have been synthesized by intercalated heteropolyanions in ionic liquid (IL)-functionalized graphene oxide (GO) via amino-protonation and/or anion-exchange reaction. This immobilization method offered improved dispersity, accessibility and stability of active sites. The amphipathic nature of IL-GO sheets and porosity of PW@IL-GO(m) are beneficial to reducing mass transfer limitation in a water/organic substrate two-phase system. Then, these obtained hybrids were employed as efficient and robust catalysts for the selective oxidation of alcohols into carbonyl compounds using hydrogen peroxide as an oxidant under organic solvent-free condition. As expected, PW@IL-GO(m) catalysts showed even much better activity than the corresponding homogeneous HPW (phosphotungstic acid) catalyst. Particularly, PW@IL-GO(1.5) gave a benzyl alcohol conversion of 94% and benzaldehyde chemoselectivity of 91%. Moreover, owing to the heterogeneous nature and strong cation–anion interactions between cationic supporter and PW anions, the as-prepared catalyst presented advantages of convenient recovery, simple preparation and steady reuse, further providing the industrial application potential in sustainable oxidation reactions.

Designing high-efficiency catalyst for the oxidation of toluene (TOL) into value-added products like benzyl alcohol, benzaldehyde and benzoic acid is of great significance in chemical industry. Herein, four type of ZIF-67 with different morphology (ZIF-67-6, ZIF-67-12, ZIF-67-18, and ZIF-67-24) are prepared by tuning the concentration of precursor. About 90% of TOL conversion is obtained in the presence of ZIF-67-24 (0.1–0.2 μm, polyhedrons) by using O2 (>99.9%, 1 atm) as oxidant at 40 °C after 4 h of reaction. Excellent performance of ZIF-67-24 could be attributed to two reasons: (I) The good crystallinity and smaller size with larger BET surface (2037 m2 g−1). (II) The electron deficient Co in ZIF-67-24 may be responded to the fast initiation of radical chain process of TOL oxidation. The research may provide a promising concept for oxidation of C-H under mild condition.

A series of new dendritic chiral salen TiIV catalysts was prepared by the covalent confinement of multiple chiral salen TiIV complexes on the periphery of a polyamidoamine (PAMAM) dendrimer through a flexible ionic liquid (IL) linker. The characterization results suggested the presence of a dendritic PAMAM scaffold, IL spacer, and intact peripheral active sites in the catalysts. The unique dendritic structure of catalysts together with a flexible IL spacer enforced the intramolecular, cooperative catalysis of asymmetric sulfoxidation to result in improved catalytic efficiency and, especially, a remarkably high selectivity. A chemoselectivity of 90 % with an enantioselectivity of 85 % was obtained in the asymmetric sulfoxidation of methyl phenyl sulfide catalyzed by the dendritic catalyst, which was significantly higher than that observed for the neat complex (64 % chemoselectivity with 68 % enantioselectivity). Furthermore, the catalysts could be recovered easily by solvent precipitation for efficient reuse.

A series of chiral salen Mn(III) polymers with build-in phase transfer capability was prepared by bridging the chiral salen Mn(III) units with polyethylene glycol (PEG)-based di-imidazolium ionic liquid (IL) side by side. Technologies of characterization suggested the alternation of intact chiral salen Mn(III) unit with PEG-based dicationic imidazolium IL moiety in the rigid one-dimension polymers. Amphipathic nature of PEG-based di-imidazolium IL moiety allowed the obtained catalysts to undergo inherent phase transfer catalysis in asymmetric epoxidation of unfunctionalized olefins with NaClO, which in turn increased the reaction rate of epoxidation in water–dichloromethane biphasic system. Decreasing total length of polyether chain leads to an increase in built-in phase transfer capability of corresponding complex, which further enhances the catalytic performance. 91–97% of conversion was obtained in the enantioselective epoxidation of styrene, α-methylstyrene, indene, 1,2-dihydronaphthalene, 6-cyano-2,2-dimethylchromene, and 6-nitro-2,2-dimethylchromene catalyzed by the complex where number of ethylene oxide unit is 3 within 60 min, which is significant higher than that observed for the neat complex (56–74%) and the ICP (62–85%). High enantiomeric excess (ee) for the epoxides (in the range of 67–93%) was also achieved, except for styrene (ee, 34%) and α-methylstyrene (ee, 41%). Furthermore, the efficient phase transfer catalysts could be easily recovered by solvent precipitation and be recycled for seven times without significant loss of the activity and enantioselectivity.

Imidazolium-based ionic liquid (IL)-functionalized graphene oxide (GO) was prepared and used to support chiral salen Mn(III) complexes. Technologies of characterization suggested that the intact chiral complex was covalently appended on flat planes and edge of the GO sheet through an imidazolium-based IL linker. The flexible layer-structure, as well as the active role of the IL linker in overall reaction, makes the novel heterogeneous catalyst efficient and universal for the enantioselective epoxidation of unfunctionalized olefins using NaClO as an oxidant. Remarkable enhancement of the reaction rate with excellent conversion (99%) was observed over a wide range of alkenes (styrene, α-methylstyrene, indene, 1,2-dihydronaphthalene, 6-cyano-2,2-dimethylchromene, and 6-nitro-2,2-dimethylchromene). The enantiomeric excess (ee) for epoxides was also encouraging (in the range of 73–93%), except for styrene (ee, 40%) and α-methylstyrene (ee, 44%). More importantly, the catalyst was perfectly stable and could be reused several times without significant loss of activity and enantioselectivity.

Keggin-type phosphotungstic acid (HPW) was incorporated into the polyamidoamine (PAMAM) matrix by partly protonating the amino groups of the PAMAM dendrimer. Characterization results suggested that the PAMAM dendrimer accommodated trivalent PW anions through ionic interactions and hydrogen bonds, resulting in novel dendritic phosphotungstate hybrids (dendri-PW hybrids). The dendritic PAMAM matrix as a countercation not only fine-tunes the redox properties of the PW anions but also has a positive “dendrimer effect” on the enhancement of the catalytic activity of the hybrids. Higher conversion of alcohols was observed over the dendri-PW hybrids in the selective oxidation of alcohols with H2O2 than over their non-dendritic counterparts. Furthermore, the dendritic ammonium cations impart reaction-controlled phase-transfer function to the dendri-PW hybrids. The catalysts precipitated from the solvent upon consumption of H2O2 and could be reused several times without loss of activity and selectivity.

A series of new metallosalen-based ionic porous organic polymers (POPs) were synthesized for the first time using a simple unique strategy based on the free-radical copolymerization reaction. Various techniques were used to characterize the physicochemical properties of these catalysts. These well-designed materials endowed high surface area, hierarchical porous structures, and enhanced CO

A simple cooperative catalytic system was successfully developed for the solvent-free N-formylation of amines with CO

A novel Mn2+/graphene oxide (Mn2+/GO) nanocomposite has been developed by coordination of the Mn2+ ions of Mn(OAc)2·4H2O with the oxygenated functional groups of the GO sheets. Characterization results strongly suggested that Mn2+ ions were dispersed homogeneously on the surface or the space between GO sheets through dative bonds. The unique layered structure of the GO carrier with flexible interlayer spaces favored reagents' diffusion towards catalytic active sites, and therefore resulted in high efficiency and good universality of the heterogeneous Mn2+/GO nanocomposite in the epoxidation of alkenes with H2O2. Excellent turnover frequency (TOF) values and selectivities for the epoxides were obtained with a wide range of either bulky or less bulky alkenes (styrene, α-methylstyrene, indene and 1,2-dihydronaphthalene). Furthermore, the Mn2+/GO nanocomposite could be easily recovered and recycled for several times without significant loss of the activity and selectivity.

A novel series of PAMAM dendrimer-supported chiral salen Mn(III) complexes has been synthesized and applied to the enantioselective epoxidation of unfunctionalized olefins. Technologies of characterization clearly suggested the axial grafting of the chiral salen Mn(III) complex on the surface of PAMAM dendrimers through a phenoxy group spacer. It was found that the peripherally modified dendrimers benefited from the cooperativity between neighboring sites confined to the surface of the dendrimers, thereby enhancing the asymmetric induction of the catalyst. Higher enantioselectivity for PAMAM dendrimer-supported chiral salen Mn(III) complexes over the homogeneous counterpart was observed in the enantioselective epoxidation of unfunctionalized olefins. Furthermore, the dendritic supports imparted selective solubility properties to the catalysts. These catalysts could be easily recovered from the reaction solution by using solvent precipitation, and could be reused for several times without loss of activity and enantioselectivity.