Ionic Fe(III)-porphyrin frameworks for the one-pot synthesis of cyclic carbonates from olefins and CO₂

Abstract

In this study, the rational construction of Fe^III-centered porphyrin-based bifunctional ionic porous organic polymers (Fe-IPOP1/2) for a one-step, halogen-free, cascade transformation of olefins and CO₂ to cyclic carbonates as compared to the conventional two-step process involving epoxides is presented. The ionic polymers, Fe-IPOP1/2 showed selective and recyclable uptake of CO₂ with an interaction energy of 32.2/39.6 kJ mol⁻¹ signifying the stronger interaction of carbon dioxide with the frameworks. Both the polymers were found to be thermally stable up to 300 °C and exhibited promising catalytic performance in the one-step, halogen-free synthesis of cyclic carbonates under eco-friendly, cocatalyst/solvent-free, atmospheric pressure conditions. The excellent catalytic activity of Fe-IPOP1/2 for a one-pot synthesis of cyclic carbonates has been ascribed to the presence of highly exposed oxophilic Fe^III sites and nucleophilic Br⁻ anions in the polymers. Notably, this one-pot synthesis strategy was extended for the transformation of various substituted olefins to their respective carbonates in good yield and selectivity. Further, Fe-IPOP1 showed good reusability with retention of catalytic activity for multiple cycles of usage.

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Introduction

The major contributor to global climate destabilization is anthropogenic and naturally emitted carbon dioxide (CO₂), whose concentration is increasing day by day exceeding 400 ppm, currently.¹ This significant rise in CO₂ concentration in the atmosphere has been attributed to greater consumption of fossil fuels leading to major environmental issues like unpredictable weather patterns, global warming, ocean acidification, and so on.^2–4 To overcome this, carbon capture,⁵ storage, and utilization have been adopted globally to contain the increasing CO₂ levels in the atmosphere.^6–14 Given the plentiful amount of CO₂ in the atmosphere, its use as a non-toxic, abundant, and cheap C1-feedstock for value-added chemical and fuel production has become a major topic of interest for many researchers worldwide.^15–21 In this direction, numerous strategies have been used for the utilization of CO₂ to obtain value-added chemicals.^22–29 Among them, production of cyclic carbonates by the functionalization of epoxides using CO₂ has gained special interest due to its absolute atom economy.^30–35 Notably, cyclic carbonates are of potential utility as precursors of polymeric materials, raw materials of pharmaceuticals and cosmetics, electrolytes in batteries, and so on.^36–39 Generally, cyclic carbonates have been synthesised by coupling CO₂ with epoxides.^40–43 However, a one-pot reaction utilizing readily available olefins and CO₂ is an attractive eco-friendly strategy for the green synthesis of cyclic carbonates as compared to the conventional two-step process via the use of epoxides. Here, the catalyst employed needs to be highly reactive to catalyze the one-pot synthesis through the in situ formation of epoxides. For efficient, one-step transformation of olefins to cyclic carbonates, the catalyst should have a Lewis acidic, oxophilic metal ion such as Mn, Ti, Fe, Mo, etc. for the in situ formation of epoxides, which is favored due to the participation of the metal–oxo intermediate.^44–47 In this direction, Fe-based catalysts have attracted significant interest due to their low cost, high abundance, and non-toxicity along with facile formation of Fe^IV=O active species during the reaction. More importantly, most of the catalysts reported for the synthesis of cyclic carbonates require an additional nucleophilic cocatalyst (halide ions) for facilitating ring-opening of the epoxide step. However, green chemistry practices demand that the synthesis be carried out under environment-friendly and halide-free mild conditions. In this regard, herein we report the strategic construction of bifunctional ionic porous organic polymers, Fe-IPOP1/2, by a polymerization reaction of Fe^III–TPyP (TpyP = 5,10,15,20-tetrakis(4-pyridyl)-porphyrin) with 1,4-bis(bromomethyl)benzene/4,4′-bis(bromomethyl)biphenyl, respectively, under an inert atmosphere. Indeed, Fe-IPOP1/2 showed halogen-free CO₂ fixation activity with olefins under environment-friendly mild conditions. Furthermore, the role of Lewis acidic/oxophilic Fe^III sites was studied by preparing an analogous ionic polymer (Zn-IPOP1) using a Zn–TPyP metalloligand. Interestingly, Zn-IPOP1 did not show catalytic activity for the one-step synthesis of cyclic carbonates highlighting the need for oxophilic Fe^III sites for the one-step cyclic carboxylation of olefins. Moreover, the role of nucleophilic Br⁻ ions in halide-free cyclic carbonates synthesis was studied by preparing an analogous non-ionic polymer (Fe-POP1). Overall, this is a rare demonstration of the application of an ionic porphyrin-based polymer for the halogen-free utilization of CO₂ in a one-pot reaction of CO₂ with olefins.

Results and discussion

Synthesis and characterization

The 5,10,15,20-tetrakis(4′-pyridyl)porphyrin (TPyP) and metallated M-TPyP (M = Zn^II, Fe^III) ligand were prepared by following a reported procedure with a slight modification (see the ESI, Scheme S1†)⁴⁸ and characterized by ¹H NMR, UV-Vis, and FTIR analysis (Fig. S1–S4†). The metallated porphyrin-based ionic polymers (Zn/Fe-IPOP1) were synthesized by the polymerization reaction of Zn/Fe-TPyP with 1,4-bis(bromomethyl)benzene. However, Fe-IPOP2 was synthesized by reaction of Fe-TPyP with the 4,4′-bis(bromomethyl)biphenyl linker under an inert atmosphere as shown in Scheme 1. Furthermore, to test the role of nucleophilic Br⁻ ions on the halogen-free preparation of cyclic carbonates, an analogous non-ionic polymer (Fe-POP) was synthesized (please refer to the ESI†).⁴⁹

Scheme 1 Synthesis scheme for Zn/Fe-IPOP1 and Fe-IPOP2.

The incorporation of a Zn^II/Fe^III ion into the porphyrin ring was confirmed by the complete absence of pyrrolic N–H peaks (δ = −2.83 ppm) of the porphyrin ring in the ¹H NMR spectrum (Fig. S2†). In addition, FTIR spectra of the M–TPyP complex showed the absence of N–H stretching frequencies at 3306 cm⁻¹ supporting the incorporation of metal ions (Fig. S3†). The UV-Vis spectra of the TPyP ligand showed an intense Soret band at 418 nm [a_1u → e_g] with four Q bands [a_2u → e_g (forbidden)] at 515, 550, 592, and 648 nm (Fig. S4†). The metallation of the TPyP ligand led to a redshift in the Soret band to 428 nm and also the number of Q bands was reduced to two (560 and 600 nm) due to the symmetry change of the molecule to D_4h further supporting the metallation of the porphyrin ring (Fig. S4†).

The PXRD plots of Zn/Fe-IPOP1 and Fe-IPOP2 showed a broad peak in the 2θ region of 20–27° due to π–π stacking of porphyrin rings (Fig. S5†). New stretching frequencies at 1160 and 1629 cm⁻¹ appeared in the FT-IR spectra, which were assigned to alkyl C–N and the pyridine iminium ion (–C=N⁺–), respectively, indicating the formation of an ionic polymer (Fig. S6 and S7†).^48,50 Furthermore, an additional peak due to the aliphatic C–H stretching frequency at 2978 cm⁻¹ supporting the presence of methylene groups in the polymer was observed (Fig. S6 and S7†).⁵¹ The formation of Zn-IPOP1 was also supported by solid-state ¹³C cross-polarized magic angle spinning (CP-MAS) NMR spectra (Fig. 1a). The methylene carbon (¹³CH₂) linked to the quaternary pyridyl ammonium showed resonance at a chemical shift (δ) of 63 ppm (¹³C_a) supporting the formation of the ionic polymer. The porphyrin ring carbon linked to the pyridyl ring (¹³C_g) showed resonance peaks at δ 119 ppm while the pyridyl ring carbon (¹³C_b) connected to the porphyrin ring was observed at 152 ppm.⁵² The pyrrole ring carbons (¹³C_f and ¹³C_d) appear at δ 131 and 145 ppm, respectively. The carbons (¹³C_h and ¹³C_c) of the pyridyl ring appeared at 129 and 148 ppm, respectively.⁴⁹ The phenyl ring carbon (¹³C_e) showed a resonance peak at 132 ppm.⁴⁹

Fig. 1 (a) ¹³C CP-MAS NMR spectra, and (b) TGA plot for Fe-IPOP1 (i) and Fe-IPOP2 (ii).

The thermal stability of the polymers was examined by thermogravimetric analysis (TGA). Fe-IPOP1/2 showed a weight loss of ∼11% in the temperature range between RT and 90 °C corresponding to the loss of adsorbed solvent (acetone) molecules (Fig. 1b). Both Fe-IPOPs exhibited thermal stability up to 300 °C, similar to that of Zn-IPOP1.⁴⁹ Furthermore, SEM analysis showed spherical morphology for Fe-IPOP1/2 (Fig. S8†). The energy dispersive spectroscopy (EDS) analysis of Fe-IPOP1 revealed the presence of constituent elements in the polymer (Fig. S9†).

X-ray photoelectron spectroscopy (XPS) analysis of Fe-IPOP1/2 was performed to confirm the presence of their constituent elements. The survey spectra of Fe-IPOP1 confirmed the presence of elemental Fe, Cl, Br, C, and N (Fig. S10†). The Fe-spectra show peaks with binding energy (BE) values of 710.7 and 724.7 eV assigned to 2p_3/2 and 2p_1/2, respectively (Fig. 2a). Interestingly, the observed BE for Fe^III matches well with the reported value for the Fe^III-centered porphyrin ring, affirming the incorporation of Fe^III in the porphyrin core.^53,54 Furthermore, Cl spectra show BE peaks at 197.8 and 199.3 eV assigned to 2p_3/2 and 2p_1/2, which supports the coordination of the –Cl ion to the Fe^III center (Fig. 2b).⁵³ Furthermore, the N spectra showed two BE peaks at 398.3 and 400.6 eV due to pyrrolic nitrogen (N_P1s) of the porphyrin ring and a quaternary nitrogen (N_Q1s), respectively, which confirms the formation of the ionic polymer (Fig. 2c). The Br spectra show the appearance of two BE peaks at 68.2 and 69.1 eV assigned to 5d_5/2 and 5d_3/2, respectively (Fig. 2d). Similarly, XPS analysis of Fe-IPOP2 confirmed the presence of its constituent elements (Fig. S11†). The Fe spectra show BE peaks at 711.1 and 724.8 eV assigned to 2p_3/2 and 2p_1/2, respectively (Fig. S11†). However, the Cl spectra depict peaks at 197.9 and 199.5 eV, due to 2p_3/2 and 2p_1/2, respectively, and the N and Br spectra (Fig. S11†) are found to be similar to those of Fe-IPOP1 affirming the isostructural nature of Fe-IPOP1/2.

Fig. 2 XPS of Fe-IPOP2: (a) Fe 2p, (b) Cl 2p, (c) N 1s, and (d) Br 3d spectra.

Gas adsorption studies

N₂ adsorption of Fe-IPOP1/2 was measured to determine the porosity of the ionic polymers. The estimated BET surface area of Fe-IPOP1 (26.5 m² g⁻¹) was found to be in close agreement with the value reported for isostructural Zn-IPOP1 (16 m² g⁻¹) (Fig. S12†), whereas Fe-IPOP2 showed a relatively higher BET surface area of 77.5 m² g⁻¹ (Fig. S13†). Furthermore, pore size distribution analysis of Fe-IPOP1/2 revealed pore sizes of 6.1/8.3 Å, respectively. The relatively larger pore size in Fe-IPOP2 has been ascribed to the presence of the longer linker of 4,4′-bis(bromomethyl)biphenyl (7.2 Å) rather than 1,4-bis(bromomethyl)benzene (5.3 Å) used in Fe-IPOP1 (Fig. S14†). Furthermore, to test the CO₂-philicity of Fe-IPOP1/2, gas sorption studies were carried out. As can be seen from Fig. 3, both Fe-IPOP1/2 showed type-I isotherms with uptake of 40.6/28.6 and 64.4/43.9 cc g⁻¹ at 273 and 298 K, respectively (Fig. 3a and b). The relatively higher CO₂ uptake of Fe-IPOP2 as compared to that of Fe-IPOP1 can be correlated to its higher surface area/porosity. Furthermore, the accurate prediction of CO₂ uptake was carried out by adopting the Freundlich–Langmuir equation⁵⁵ (Fig. S15 and S18†) and the adsorption energy (Q_st) was determined from the Clausius–Clayperon equation.⁵⁶ Interestingly, the Q_st for CO₂ with Fe-IPOP1/2 was calculated and found to be 32.2/39.6 kJ mol⁻¹ signifying the stronger interaction of carbon dioxide with the frameworks (Fig. S19 and S20†). Additionally, selective gas sorption measurements (Fig. 3c) revealed negligible uptake of N₂, and CH₄ with relatively high Henry gas selectivity constants of 71 and 69 for K_CO2/N2 and K_CO2/CH4, respectively (Fig. S21†). Notably, Fe-IPOP1 showed recyclable CO₂ adsorption properties (Fig. 3d). Furthermore, the basic and acidic strengths of Fe-IPOP1 quantified by CO₂ and NH₃ TPD (temperature-programmed desorption) analysis were found to be 0.46 and 0.53 mmol g⁻¹, respectively (Fig. S22†). Thus, the TPD analysis revealed the bifunctional nature of Fe-IPOP1 having moderate basic and acidic sites, which is an essential requirement for effective transformation of CO₂ under mild conditions.

Fig. 3 CO₂ adsorption isotherms for (a) Fe-IPOP1 and (b) Fe-IPOP2. (c) Selective CO₂ adsorption isotherm, and (d) recyclable CO₂ adsorption for Fe-IPOP1.

Catalytic epoxidation reaction of olefins to epoxides

The presence of oxophilic/Lewis acidic Fe^III and nucleophilic (Br⁻) sites in Fe-IPOP1/2 motivated us to test their catalytic performance for one-pot, halogen-free fixation of readily available olefins with CO₂ to produce valuable feedstocks, that is cyclic carbonates. It is worth noting that the majority of reports on cyclic carbonates describe utilizing epoxides, which are prepared by the epoxidation of olefins catalyzed by Lewis acidic metal ions.^57–61 Hence, to establish the formation of an epoxide as an intermediate en route to the formation of cyclic carbonates, the catalytic activity of Fe-IPOP1/2 was tested for the generation of epoxides from olefins using PhIO as an oxidizing agent at RT. The catalytic conditions were optimized using styrene as a model substrate by varying the reaction parameters (Table S1†). Notably, both Fe-IPOP1/2 catalyzed the epoxidation of styrene to yield styrene oxide (SO) with more than 99% yield within 18 h at RT with 100% selectivity (Table 1 and Fig. S23, S24†). Furthermore, to check the role of Fe^III ions in catalyzing the epoxidation reaction, a control experiment was carried out using analogous Zn-centered porphyrin POP (Zn-IPOP1) as a catalyst. To our delight, negligible conversion (<5%) of styrene to SO was observed under the optimized conditions (Fig. S25†). This study highlights the importance of oxophilic Fe^III ions for the oxidization of olefins to epoxides. Furthermore, the catalytic study was extended to the oxidation of various olefins including both substituted styrenes and linear alkenes (Table 1). Interestingly, most of the olefins were found to undergo conversion to their respective oxides with high yield and selectivity (Table 1).

Table 1 The catalytic activity of Fe-IPOP1/2 for epoxidation of olefins^a

S. no.	Substrate	Product	Catalyst	Conversion (%)^b	TON^c
a Reaction conditions: olefin (1 mmol), catalyst (10 mg), PhIO (1.5 mmol), temperature (25 °C), and time (18 h). b The catalytic conversion was determined by ^1H NMR analysis. c TON = number of mmol of product formed/number of mmol catalyst used.
1			Zn-IPOP1	—	—
2			Fe-IPOP1	>99	143
3			Fe-IPOP2	>99	140
4			Fe-IPOP1	95	136
5			Fe-IPOP1	89	127
6			Fe-IPOP1	83	119
7			Fe-IPOP1	78	111
8			Fe-IPOP1	76	109
9			Fe-IPOP1	71	101
10			Fe-IPOP1	66	94

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One-step cyclic carbonate synthesis from olefins and CO₂

The high catalytic activity of Fe-IPOP1/2 towards epoxidation of both aromatic and aliphatic olefins motivated us to test their catalytic performance for one-pot cyclic carbonate synthesis using readily accessible olefins and CO₂ (Fig. 4a). To start with, the catalysis was performed using styrene as a model substrate and the reaction conditions were optimized by varying the temperature and time of reaction (Fig. 4 and Table S2†). Under the optimized reaction conditions, Fe-IPOP1 catalyzed the one-step oxidative carboxylation of styrene to styrene carbonate (SC) with >99% conversion within 24 h under halogen-free mild conditions of 1 atm of CO₂ (Fig. 4 and S26, S27, Table S2†). Furthermore, controlled experiments performed using polymer precursors i.e. Fe-TPyP, 1,4-bis(bromomethyl)benzene, 4,4′-bis(bromomethyl)biphenyl and FeCl₃ did not show styrene carbonate formation (Table S2†), highlighting the essential requirement of Fe-IPOP1 for generating cyclic carbonates from olefins and CO₂. Thus, the control experiments revealed that for one-pot, halogen-free transformation of CO₂ to cyclic carbonates both oxophilic metal and nucleophilic halogen sites are essential. In the case of Fe-TPyP and FeCl₃ catalyzed reactions, although the presence of an oxophilic metal site is fulfilled, the nucleophilic Br⁻ sites are absent, which are necessary for promoting ring-opening of the epoxides and therefore results in no formation of cyclic carbonates. Furthermore, the catalytic activity carried out with Fe-IPOP2 as the catalyst showed almost similar results to that of Fe-IPOP1 with >99% conversion of styrene to SC (Fig. S28†). The efficient halogen-free catalytic activity of Fe-IPOP1 was further extended for one-step cyclic carboxylation of various olefins including substituted styrenes and linear alkenes to their respective cyclic carbonates. Interestingly, Fe-IPOP1 catalyzed the transformation of a series of olefins to cyclic carbonates under halogen-free optimized conditions and the catalytic conversions are summarized in Table 2 (Fig. S29–S32†). The relatively lower conversion of long-chain linear alkenes, say 1-hexene (73%), 1-octene (69%), and 1-decene (64%), has been ascribed to their bulkiness and lower π-electron density.⁶² Notably, a comparison of the catalytic activity of Fe-IPOP1 with reported systems revealed its superior performance for one-step cyclic carbonate synthesis from readily accessible olefin and CO₂ (Table 3).

Fig. 4 (a) Catalytic one-pot synthesis of cyclic carbonates. Optimization of the catalytic reaction by varying the temperature (b) and time (c).

Table 2 Catalytic one-step synthesis of cyclic carbonates from olefin and CO₂^a

S. no.	Substrate	Product	Catalyst	Conversion^c (%)	Selectivity for CC^d	TON^e
a Reaction conditions: olefin (1 mmol), catalyst (10 mg), PhIO (1.5 mmol), CO2 (1 bar), DCM (2 mL), temperature (80 °C), and time (24 h). b Catalyst (non-ionic polymer), Fe-POP (10 mg). c Catalytic conversion was determined by ^1H NMR analysis. d The selectivity is calculated based on cyclic carbonate and the rest of the product corresponds to epoxide. e TON = number of mmol of product formed/number of mmol of catalyst used.
1			Zn-IPOP1	—	—	—
2			Fe-IPOP1	>99	96	137
3			Fe-IPOP2	>99	97	139
4			Fe-IPOP1	96	93	133
5			Fe-IPOP1	91	89	127
6			Fe-IPOP1	86	82	117
7			Fe-IPOP1	78	74	106
8			Fe-IPOP1	73	72	103
9			Fe-IPOP1	69	67	96
10			Fe-IPOP1	64	62	89
11^b			Fe-POP	>99	97	138

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Table 3 Comparison of catalytic activity of Fe-IPOP1 for one-step synthesis of styrene carbonates with that of literature-reported catalysts

S. no.	Catalyst	Co-catalyst	Pressure	Temperature (°C)	Conversion (%)	Ref.
1	ZnW PYIs14	TBABr	05	50	92	63
2	MOF-590	TBABr	01	80	93	64
3	MNP@SiO2–8Mn	PPNCl	10	80	99	65
4	Ti-MMM-E	TBABr	08	70	92	66
5	Fe^III@MOF1	TBABr	08	80	98.6	67
6	MOF-892	TBABr	01	80	51	68
7	ImBr-MOF-545(Mn)	—	05	70	99	59
8	Fe-IPOP1	Halogen free	01	80	99	This work

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Mechanistic investigation for one-step cyclic carboxylation of olefins

As discussed in the aforementioned section, the one-step cyclic carbonate synthesis from olefins and CO₂ proceeds through the formation of an epoxide intermediate. To establish the in situ formation of epoxide, the progress of the catalysis was monitored by a time-dependent ¹H NMR study. As shown in Fig. 5, ¹H NMR spectra of the aliquot taken at 6 h showed peaks corresponding to styrene oxide along with the product, styrene carbonate, and reactant, styrene (Fig. 5). Furthermore, as the reaction time increased to 18 h, the intensity of the peaks due to styrene oxide decreases and that of styrene carbonate increases, and at 24 h only peaks due to the SC are observed. This study unambiguously confirms the in situ generation of styrene oxide during the one-step cyclic carboxylation of olefins. Once the styrene oxide (epoxide) is formed, its coordination to a Lewis acidic (Fe^III) site leads to the polarization of the epoxide into which insertion of a CO₂ molecule takes place. Furthermore, to confirm the interaction of epoxide with the Fe^III site, a control experiment was carried out in which Fe-POP1 catalyst was treated with epoxide (styrene oxide) for 2 h and then the catalyst was recovered and washed thoroughly with methanol followed by drying at 80 °C under vacuum. The FT-IR spectra of the recovered sample showed peaks due to styrene oxide, supporting the polarization of styrene oxide at Fe^III sites (Fig. S33†). This step is followed by ring-opening of SO by nucleophilic Br⁻ ions of the polymer. To support this step, an analogous polymer, Fe-POP, which lacks free Br⁻ ions, was synthesized (Scheme S2†) and its catalytic performance tested in the one-step cyclic carbonate synthesis under identical conditions.⁴⁸ To our delight, only styrene oxide (>99) formation was observed as opposed to styrene carbonate formation as in the case of Fe-POP1 (Table 2). However, the addition of a cocatalyst (2.5 mol% TBABr) to the reaction led to the formation of styrene carbonate. These studies brought out the essential requirement of a bifunctional catalyst composed of acidic and nucleophilic sites to achieve a one-step synthesis of cyclic carbonates under halogen-free conditions.

Fig. 5 Time-dependent ¹H NMR (400 MHz, CDCl₃, 20 °C) spectra for one-pot styrene carbonate synthesis.

Based on the above discussion, the mechanism for the one-step cascade reaction of CO₂ with styrene catalyzed by a bifunctional Fe-POP1 catalyst is shown in Scheme 2. The direct carboxylation of styrene proceeds with the in situ generation of styrene oxide by the oxidation of styrene. Then polarization of styrene oxide at the Fe^III sites, followed by its ring-opening upon nucleophilic attack of a Br⁻ anion, results in a bromo-alkoxide intermediate. Then the subsequent addition of CO₂ produces metal carbonate species and its ring-closure reaction leads to styrene carbonate and its elimination regenerates the catalyst.

Scheme 2 Plausible mechanism for catalytic one-pot reaction of CO₂ with an olefin to generate cyclic carbonates.

Recyclability and catalyst leaching test

Chemical stability and reusability are essential requirements for a heterogeneous catalyst. The reusability of Fe-IPOP1 was investigated by isolating it from the reaction mixture followed by activation at 100 °C for 12 h. It is important to note that Fe-IPOP1 was reusable for eight cycles with no significant loss of activity (Fig. 6a and S34†). Additionally, PXRD, FTIR, and XPS analyses of the regenerated polymer confirm its structural stability (Fig. S5, S35 and S36†). Furthermore, the BET surface area (22.3 m² g⁻¹) of the recycled sample was found to be almost close to that of the as-synthesized sample (26.5 m² g⁻¹), supporting retention of the original network structure even after eight catalytic cycles. To exclude any leaching of active metal (Fe^III) into the homogeneous system, the reaction was halted after 8 h and the catalyst was separated by filtration, and the reaction was continued for some more time. Surprisingly, no discernible rise in conversion was detected, indicating the absence of leaching of active species into solution (Fig. 6b). Furthermore, MP-AES analysis of the reaction filtrate showed no detectable Fe^III ions in the solution, which rule out any leaching during catalysis (Fig. S37†).

Fig. 6 (a) Catalyst reusability and (b) leaching test.

Conclusion

In summary, a strategic design of bifunctional Fe-porphyrin-based ionic POP by integrating oxophilic Fe sites and nucleophilic Br⁻ anions essential for the one-pot synthesis of cyclic carbonates under eco-friendly and halogen-free conditions is presented. The role of oxophilic and nucleophilic sites in catalytic activity was established. Importantly, Fe-IPOP1 showed excellent reusability with retention of catalytic performance and structural integrity. This work constitutes the first demonstration of an ionic Fe-porphyrin polymer-catalyzed one-pot synthesis of cyclic carbonates from readily accessible olefins and carbon dioxide.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

CMN thanks the Science & Engineering Research Board (SERB), Department of Science and Technology, Govt. of India, for financial support (CRG/2018/001176). R. D. and S. K. thank IIT Ropar for their fellowships.

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Footnote

† Electronic supplementary information (ESI) available: Synthesis procedures, FTIR plots, UV-Vis spectra, and ¹H NMR spectra of the catalytic reactions. See DOI: https://doi.org/10.1039/d2qi02599j

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