Efficient single-component nickel catalysts with tetradentate aminopyridine ligands for cycloaddition reactions of CO₂ and epoxides under mild conditions

Abstract

A series of single-component nickel catalysts (L1-NiBr₂/L2-NiBr₂/L3-NiBr₂) with tetradentate aminopyridine ligands are presented, which exhibit excellent capabilities and selectivity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. A green crystal of L1-NiBr₂ was obtained in CH₃CN, and the ligand adopted a cis-α conformation in the complex. The conversion of styrene oxide could reach 98%, providing 100% selectivity at 90 °C, 1 MPa CO₂ pressure and 5 mol% of L1-NiBr₂ under solvent-free conditions, while the yield and selectivity values were still as high as 92% and 99%, respectively, under 1 atm CO₂ and 0.5 mol% of the catalyst at the same temperature. The catalysts also exerted efficient catalytic coupling reactions of terminal epoxides (90–98% yields of cyclic carbonates), except those bearing a long aliphatic chain under mild conditions. The catalyst exhibited excellent recyclability and stability, which were further proved through ICP to test the catalyst leaching, TGA and IR spectra. Moreover, the catalytic cycloaddition reaction mechanism was investigated using density functional theory (DFT) calculations.

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Sustainability spotlight

The rapid increase in CO₂ emission has had an adverse impact on the environment; therefore, developing sustainable chemical processes to transform CO₂ into value-added chemicals is crucial. This study focuses on the production of efficient single-component nickel catalysts with tetradentate aminopyridine ligands and their application for transforming CO₂ into cyclic carbonates. The investigation demonstrated that the developed nickel catalysts presented excellent bifunctional catalytic performance, stability and substrate scope under mild conditions, even in low catalyst amounts and atmospheric pressure of CO₂ in the absence of solvent, which is industrially attractive for future applications. Our technologies align with the United Nations Sustainable Development Goals, particularly Goals 9, 12 and 13.

1. Introduction

As a potent greenhouse gas, carbon dioxide (CO₂) emissions have increased worldwide on a massive scale due to the generation of energy by the combustion of fossil fuels, adversely impacting the environment.¹ Thus, reducing the level of atmospheric CO₂ is of utmost importance in the coming decade. In contrast, CO₂ is a very significant C1 feedstock in organic synthesis due to its non-flammable, non-toxic, sustainable and inexpensive characteristics.² Therefore, the transformation of CO₂ into industrially attractive chemicals by chemical strategies has attracted increasing attention.³ Among them, the production of cyclic carbonates from epoxides and CO₂, as an atom-economical reaction, is regarded a considerate method.⁴ Moreover, cyclic carbonates have a vibrant area of application in academic and industrial arenas, such as polar aprotic solvents, electrolytes in lithium-ion batteries, and intermediates of biodegradable polymers.⁵

A crucial challenge in the reaction between epoxides and CO₂ is the development of suitable catalysts due to the high thermodynamic stability of CO₂.⁶ To date, numerous catalytic systems, which usually contain both a Lewis acidic center to activate the C–O bond of the epoxide and a Lewis basic site that can be used as a nucleophilic reagent to open the epoxide ring, have been successfully synthesized, including organo-catalysts,⁷ metal complexes catalysts,⁸ organic frameworks⁹ and others, to catalyze the cycloaddition reaction.¹⁰ Among these active catalytic systems, metal-containing catalysts have attracted increasing attention due to their higher intrinsic Lewis acidity, lower catalyst loadings and lower reaction temperatures.¹¹ However, most of them are binary catalytic systems, and Lewis bases are usually added as co-catalysts, such as DMAP (4-dimethylaminopyridine) or onium salts.^8c,12 Consequently, considerable efforts to develop efficient one-component bifunctional metal catalyst systems have been proposed to promote cyclic carbonate synthesis without co-catalysts.

As a part of the metal complex, ligands play a pivotal role in developing bifunctional metal catalysts with high catalytic reactivity, and tetradentate nitrogen ligands have been proven efficient for various oxidation reactions, as well as the conversion of CO₂.¹³ In view of this, a series of tetradentate aminopyridine-containing metal catalysts have been designed for the transformation of CO₂.¹⁴ For example, various kinds of bifunctional zinc coordination compounds with tetradentate aminopyridine (N4) ligands have been proven efficient catalysts for the coupling reaction between CO₂ and epoxides with a broad substrate scope under solvent-free conditions by Sun et al.^14a Despite of this, the development of novel N4 bifunctional catalysts under milder conditions is still needed.

In order to achieve the goal, a more active metal center is of utmost importance to obtain high catalytic activity.¹⁵ Nickel (Ni) is inexpensive and earth-abundant, and nickel complexes usually exhibit distinct properties in small molecule activation chemistry and redox chemistry, such as functionalization of alkene and CO₂.¹⁶ Moreover, nickel complexes have been rarely reported for direct coupling of CO₂ with epoxides.¹⁷

Encouraged by this, metal complexes composed of nickel and N4 were synthesized, and their catalytic activity for the coupling of epoxides and CO₂ to produce cyclic carbonates in the absence of co-catalysts have been evaluated (Scheme 1) and found to be efficient bifunctional catalysts without a co-catalyst. Moreover, a plausible mechanism for the coupling reaction was investigated by density functional theory (DFT).

Scheme 1 The cycloaddition reaction of CO₂ and epoxides catalyzed by the Ni complex.

2. Experimental

2.1 General information

Solvents and chemicals obtained from various companies, such as Aladdin and Macklin, were used without further purification unless stated otherwise. Analytical thin-layer chromatography (TLC) was carried out using 0.25 mm commercial silica gel plates. The purification of product was carried out by flash chromatography using silica gel (200–300 mesh). NMR spectra were performed at 298 K on a Bruker 400. Chemical shift values for ¹H and ¹³C are reported as δ values (ppm) relative to the deuterated solvent and coupling constants (J) in Hz. Single-crystal X-ray diffraction measurements were carried out on a Bruker Smart APEX II CCD diffractometer at 100 (2) K using Cu Kα radiation (λ = 1.54184 Å). High-resolution mass spectroscopy experiments were carried out with a Bruker Daltonics microTOF-QII mass spectrometer. The gas chromatography (GC) was recorded by a Shimadzu GC-2010, SE-54 column using diphenyl as the internal standard. Infrared spectra were recorded with a Thermo Scientific Nicolet IS50-IR spectrometer at room temperature.

2.2 Synthesis and characterization of nickel complexes

The ligands L1–L3 were prepared using previously reported methods.¹⁸

2.2.1 Synthesis of nickel complexes. An acetonitrile solution of ligand (1.1 mmol) was added dropwise to a stirred solution of NiBr₂ (1.0 mmol) or other metal salts in 5 mL anhydrous acetonitrile. The mixture was stirred at 50 °C for 24 h and then cooled to room temperature (Scheme 2). The anhydrous acetonitrile was removed by rotary evaporation, and the solid was washed three times with 15 mL anhydrous ether to obtain the nickel complexes.

Scheme 2 Synthesis of nickel complexes.

2.2.1.1 L1-NiBr₂ . Green solid (92%, yield), m. p. 112–114 °C, HRMS (ESI-MS) m/z: calcd for C₂₀H₂₈BrN₄Ni [M–Br]⁺: 461.0851, found: 461.0845.
2.2.1.2 L2-NiBr₂ . Green solid (90%, yield), m. p. 120–122 °C, HRMS (ESI-MS) m/z: calcd for C₃₂H₃₆BrN₄Ni [M–Br]⁺: 613.1477, found: 613.1473.
2.2.1.3 L3-NiBr₂ . Green solid (90%, yield), m. p. 130–132 °C, HRMS (ESI-MS) m/z: calcd for C₄₀H₄₀BrN₄Ni [M–Br]⁺: 713.1790, found: 713.1786.
2.2.1.4 L1-NiCl₂ . Green solid (93%, yield), m. p. 110–112 °C, HRMS (ESI-MS) m/z: calcd for C₂₀H₂₈ClN₄Ni [M–Cl]⁺: 417.1356, found: 417.1350.
2.2.1.5 L1-NiI₂ . Green solid (92%, yield), m. p. 110–112 °C, HRMS (ESI-MS) m/z: calcd for C₂₀H₂₈IN₄Ni [M–I]⁺: 509.0712, found: 509.0707.
2.2.1.6 L1-Ni(OTf)₂ . Blue solid (90%, yield), m. p. 60–62 °C, HRMS (ESI-MS) m/z: calcd for C₂₁H₂₈F₃O₃SN₄Ni [M-OTf]⁺: 531.1188, found: 531.1182.
2.2.1.7 L1-Ni(OAc)₂ . Blue solid (91%, yield), m. p. 60–62 °C, HRMS (ESI-MS) m/z: calcd for C₂₂H₃₁O₂N₄Ni [M–OAc]⁺: 441.1800, found: 441.1795.

2.3 General procedure for the synthesis of cyclic carbonates

Epoxides (1 mmol) and a specified amount of nickel complexes are added to a 25 mL high-pressure vessel along with magnetic particles in the presence of CH₃CN (2 mL) or solvent-free. The internal gas is then replaced with CO₂ three times. The reaction mixture is stirred at the desired temperature for the required time, and the remaining CO₂ is slowly released after cooling the high-pressure vessel to room temperature. The conversion rate of epoxides and the yield of cyclic carbonates are determined by analyzing the crude product with gas chromatography when biphenyl is used as the internal standard. The calculation formula of conversion, yield, selectivity, and TON are given in the ESI.†

3. Results and discussion

The L1-NiBr₂ powder was dissolved in CH₃CN solution and recrystallized at room temperature for a few days, and then a green crystal was obtained. Its structure was characterized by X-ray diffraction analysis, and the Oak Ridge thermal ellipsoid plot (ORTEP) diagram described in Fig. 1 shows that the ligand coordinated with nickel bromide using four N atoms in a cis-α topology. The data collection and structure refinement are shown in Table S1,† and selected bond lengths and bond angles are summarized in Table S2.†

Fig. 1 ORTEP diagram of the nickel complex L1-NiBr₂ (CCDC: 2307070). The hydrogen atoms are omitted for clarity in the metal complex.

3.1 Optimization of the reaction conditions

Originally, L1-NiBr₂ was used to investigate the bifunctional catalytic performance for the coupling reaction of CO₂ and styrene oxide (1a) in the presence of 2 mL CH₃CN under the conditions of 2.5 MPa CO₂ and 80 °C for 8 h. It could be seen that the conversion of 1a and the yield of styrene carbonate (2a) were 95% and 94% with the selectivity of 99% when 5 mol% of L1-NiBr₂ was added alone and no co-catalyst was used, which indicated that L1-NiBr₂ was an efficient bifunctional catalyst (Table 1, entry 1). Under the same conditions, the effects of common solvents such as CH₃CN, DCE (dichloroethane), toluene, CH₃OH, DMC (dimethyl carbonate), DMF (N,N-dimethylformamide), THF (tetrahydrofuran) and solvent-free for the catalytic performance were investigated (Tables S3† and 1, entry 2). The result showed that the catalytic system performed the highest conversion and yield with 100% selectivity in the absence of solvent (Table 1, entry 2). Consequently, the catalytic performance of the cycloaddition between CO₂ and 1a could be optimized without any co-catalyst under solvent-free conditions in the next test.

Table 1 Optimization of the reaction conditions for the catalytic cycloaddition reaction between 1a and CO₂^a

Entry	Cat.	t (h)	P (MPa)	Conv.^b (%)	Yield^b (%)	Sel.^b (%)
a Reaction conditions: 1 mmol styrene oxide (1a), catalyzed by 5 mol% of catalyst at 80 °C with solvent-free. b Determined by gas chromatography using biphenyl as the internal standard. c In CH3CN (2 mL). d 1 mol% of L1-NiBr2. e 3 mol% of L1-NiBr2. f 7 mol% of L1-NiBr2.
1^c	L1-NiBr2	8	2.5	95	94	99
2	L1-NiBr2	8	2.5	98	98	100
3	L1-NiBr2	4	2.5	99	98	99
4	L1-NiBr2	2	2.5	99	98	99
5	L1-NiBr2	1	2.5	98	98	100
6	L1-NiBr2	0.5	2.5	86	78	91
7	L1-NiBr2	1	1.5	98	98	100
8	L1-NiBr2	1	1.0	98	98	100
9	L1-NiBr2	1	0.5	92	88	96
10	L1-NiBr2	1	0.1	59	57	97
11^d	L1-NiBr2	1	1.0	51	50	99
12^e	L1-NiBr2	1	1.0	96	94	98
13^f	L1-NiBr2	1	1.0	98	97	99
14	L1-NiCl2	1	1.0	85	79	93
15	L1-NiI2	1	1.0	98	96	98
16	L1-Ni(OAc)2	1	1.0	31	—	—
17	L1-Ni(OTf)2	1	1.0	30	—	—
18	L2-NiBr2	1	1.0	95	95	100
19	L3-NiBr2	1	1.0	97	96	99
20	L1	1	1.0	8	—	—
21	NiBr2	1	1.0	22	—	—

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When the reaction temperature decreased from 80 °C to 60 °C, the conversion of 1a and the yield of 2a reduced to 59% and 56%, respectively (Table S4,† entries 1–3). At the same time, the selectivity of the coupling reaction decreased from 100% and 95%, respectively. Increasing the reaction temperature from 80 °C to 90 °C, the conversion and the yield would not decrease, presenting the stability of this catalytic system at higher temperatures (Table S4,† entries 3 and 4). The impact of reaction time on the catalytic performance was next studied with 5 mol% of L1-NiBr₂ as the catalyst at 80 °C under 2.5 MPa CO₂ pressure (Table 1, entries 3–6). Gradually decreasing the reaction time from 8 to 1 h, all of the reactions gave complete conversion from 1a to 2a. The conversion and selectivity would be turned to 86% and 91%, respectively, when the reaction time is reduced to 0.5 h. Therefore, 1 h is a more appropriate reaction time for the coupling reaction.

To further investigate more economical reaction conditions, the effect of CO₂ pressure was examined, and good activity could be observed (98% conversion of 1a and 98% yield of 2a) under 1 MPa CO₂ (Table 1, entries 7 and 8). However, the conversions of 1a were 59% and 92%, accompanied by 57% and 88% yields of 2a, when the CO₂ pressures were 0.1 and 0.5 MPa, respectively (Table 1, entries 9 and 10). Despite the lower conversions of 1a to 2a, both presented a satisfactory selectivity (97% at a CO₂ pressure of 0.1 MPa and 96% at a CO₂ pressure of 0.5 MPa) (Table 1, entries 9 and 10). As described in Table 1 (entries 8 and 11–13), the amounts of catalyst were investigated under the conditions of 1 MPa CO₂ and 80 °C for 1 h with L1-NiBr₂ as the catalyst. It could be found that 5 mol% of L1-NiBr₂ was enough to catalyze the coupling reactions of CO₂ with epoxides (Table 1, entry 8).

Then, the activities of several nickel complexes were assessed. Compared to L1-NiBr₂, L1-NiCl₂ was a little sluggish, and 2a was isolated in 79% yield, owing to a lower nucleophilicity of Cl⁻ (Table 1, entry 14). Although the nucleophilicity of I⁻ is stronger than Br⁻, L1-NiBr₂ showed similar transformation and yield, which may be attributed to the steric hindrance effect of I⁻ (Table 1, entry 15).¹⁹ However, 2a was not tested, providing 31% or 30% conversion of 1a by employing L1-Ni(OAc)₂ or L1-Ni(OTf)₂ as the catalyst, due to the bulky steric hindrance and weak nucleophilicity of OAc⁻ and OTf⁻ (Table 1, entries 16 and 17).²⁰ Besides, 5 mol% of L2-NiBr₂ or L3-NiBr₂ was added into this coupling reaction system to evaluate the effect of the ligand on the catalytic performance under the conditions of 1 MPa CO₂ and 80 °C for 1 h, which also presented satisfactory catalytic ability due to their analogous scaffold (Table 1, entries 18 and 19). The activity of L-NiBr₂ would not be affected by the steric hindrance and electronic property of the ligands. That is to say, anion, as a nucleophilic reagent to open the epoxide ring, played an important role in the reaction. Considering L1 as a much cheaper ligand than the others, L1-NiBr₂ was the optimized catalyst for the cycloaddition reaction between epoxides and CO₂. When ligand L1 (5 mol%) or NiBr₂ (5 mol%) was added separately for the cyclization reaction, the conversion of 1a was just 8% or 22% with no 2a tested in the same conditions (Table 1, entries 20 and 21). The results indicated that there were synergistic catalytic effects between L1 and NiBr₂. After all, one of the optimized conditions is 1 MPa CO₂ pressure and 80 °C for 1 h catalyzed by 5 mol% L1-NiBr₂ under solvent-free.

In order to investigate milder and more commercial reaction conditions, the pressure of CO₂ and the amount of catalyst have been explored. Based on the above-investigated conditions (Table 1, entry 8), the conversion of 1a was 95%, and the selectivity was about 100% after stirring at 80 °C for 8 h under 1 atm CO₂ (Table 2, entry 1). Consequently, 92% conversion and 92% yield were still obtained when the amount of catalyst decreased to 1 mol% (Table 2, entry 2). With the extension of reaction time, there was no obvious assistance to improve the yield of 2a (Table 2, entry 3). In contrast, the conversion of 1a/yield of 2a could be increased from 65%/64% to 92%/91% accompanied by prolonging the reaction time from 8 h to 14 h when the amount of catalyst was 0.5 mol% (Table 2, entries 4 and 5). However, the conversion of 1a and the yield of 2a were still less than 80%, even at 80 °C for 24 h at 1 atm CO₂ pressure, when the amount of catalyst reduced to 0.2 mol% (Table 2, entries 6 and 7). In conclusion, the investigated milder reaction conditions were 1 atm CO₂ and 80 °C for 14 h with 0.5 mol% L1-NiBr₂ as the catalyst under solvent-free conditions. It was worth noting that the catalytic system also exhibited great catalytic activity, providing 88% conversion and 85% yield by extending the amount of styrene oxide (1a) to 10 mmol (1.20 g) under the optimized conditions (Table 2, entry 8).

Table 2 Investigation of milder conditions for the coupling reaction between 1a and CO₂ under 1 atm CO₂^a

Entry	Amount of catalyst (mol%)	t (h)	Conv.^b (%)	Yield^b (%)	Sel.^b (%)	TON
a Reaction conditions: 1a (1 mmol), 80 °C, 1 atm CO2, solvent-free. b Gas chromatography is used to determine the conversion rate and yield of cyclic carbonates, with biphenyl as the internal standard. c 10 mmol styrene oxide (1a).
1	5	8	95	95	100	19
2	1	8	92	92	100	92
3	1	12	96	94	98	94
4	0.5	8	65	64	99	128
5	0.5	14	92	91	99	182
6	0.2	12	46	46	100	230
7	0.2	24	76	74	98	370
8^c	0.5	14	88	85	97	170

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The stability of catalyst L1-NiBr₂ was investigated by recycling experiments using 1a (1 mmol) as the model substrate under 1 atm CO₂ pressure at 80 °C for 14 h with no solvent added. After the first 14 h period, the yield of 2a was determined by gas spectroscopy, and the reaction mixture was then washed with anhydrous diethyl ether (5.0 mL) to remove 2a and 1a and dried. Subsequently, the system was directly added to another 1 mmol 1a to complete the next circulation. As listed in Fig. 2, this procedure could be repeated five times with almost no loss of its catalytic activity (the yields of 2a were 92%, 92%, 90%, 91%, and 91%, respectively). The ICP test recorded a 0.76% catalyst leaching in every recycling. The recycling experiments further proved that the catalytic system of L1-NiBr₂ is stable and efficient for the coupling of CO₂ and epoxides under mild conditions. It is worth noting that the stability of L1-NiBr₂ could also be verified by the TGA (thermogravimetric analysis) and IR spectra, which exhibited almost no changes between before and after the cyclic experiment (Fig. S1 and S2†).

Fig. 2 Recyclability of catalyst L1-NiBr₂ for the coupling of CO₂ and 1a (1 mmol).

3.2 Extend the epoxide substrates

In addition, to investigate the potential and general applicability of the bifunctional catalyst L1-NiBr₂, the coupling reactions between CO₂ and a variety of epoxides were investigated under the above two optimal reaction conditions. It should be noted that L1-NiBr₂ exhibited a good catalytic performance with more than 90% of yield for the transformation of substituted epoxides 1a–1f bearing various aliphatic and aromatic groups, such as phenyl, methyl, chloromethyl, alkenyl and ether groups under both optimal conditions (Table 3, entries 1–6). However, when the substituted group was a long aliphatic chain, the yields of 2g decreased to 42% and 35% under the two optimal conditions due to its weak dissolvability for the catalyst (Table 3, entry 7). Fortunately, under the same conditions, increasing the reaction time from 1 h to 6 h, the yield of 2g would be increased from 42% to 95%. However, the internal epoxide 1h gave the lowest yield under different reaction conditions due to its steric hindrance (Table 3, entry 8).

Table 3 Substrate scope for cyclic carbonate synthesis

Entry	Epoxide	Product	Yield^a^,^b (%)	Yield^a^,^c (%)
a Isolated yield. b Reaction conditions: 1 mmol epoxide, 1 MPa CO2, 80 °C, 1 h, 5 mol% (relative to the epoxide) L1-NiBr2, solvent-free. c Reaction conditions: 1 mmol epoxide, 1 atm CO2, 80 °C, 14 h, 0.5 mol% (relative to the epoxide) L1-NiBr2, solvent-free. d 6 h.
1			98	91
2			95	92
3			97	90
4			91	95
5			92	95
6			92	95
7			42(95^d)	35
8			10	6

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3.3 Unravelling the reaction mechanism with DFT calculations

The catalytic mechanism of the coupling reaction of epoxide and CO₂ was explored with DFT calculations. Initiation of the catalytic cycle involves a ligand substitution process in which one Br⁻ leaves the Ni coordination sphere in exchange for an epoxide. Then, the Br⁻ rebinds to form IM3 before a nucleophilic attack occurs on the epoxide ring, yielding IM4 (Fig. 3). A 4.9 kcal mol⁻¹ Gibbs free energy barrier was estimated for this ring-opening process. Next, the addition of CO₂ occurs, in which the C atom of CO₂ weakly binds the O atom originally from the epoxide and currently coordinating to Ni, giving IM5 (Fig. 4). The insertion of CO₂ into the Ni-coordinated bromoethanolate is computed to have a 4.4 kcal mol⁻¹ Gibbs free energy barrier. The final step is the ring closure of the bromoethyl carbonate ligand in IM6, which is calculated to be the rate-determining step with a Gibbs free energy barrier of 18.7 kcal mol⁻¹ (Fig. 4). Releasing the ethyl carbonate molecule closes the catalytic cycle with a net ΔH of −21.5 kcal mol⁻¹. A summary of the proposed reaction mechanism, as per previous reports, is shown in Scheme 3.²¹

Fig. 3 Energy profile for the binding of the L1-NiBr₂ catalyst with the ethylene oxide substrate, followed by the nucleophilic ring opening process. The relative Gibbs free energies and the relative electronic energies (in parentheses) in kcal mol⁻¹ are labelled.

Fig. 4 Energy profile for the conversion from the CoN₄BrOCH₂CH₂Br intermediate (IM4) to the final product, ethylene carbonate (EC). The original L1-NiBr₂ catalyst was selected to be the zero-energy scale to stay consistent with Fig. 3. The relative Gibbs free energies and the relative electronic energies (in parentheses) in kcal mol⁻¹ are labelled.

Scheme 3 A proposed mechanism for the cycloaddition reaction catalyzed by L1-NiBr₂.

4. Conclusion

In summary, novel bifunctional single-component nickel catalysts with tetradentate aminopyridine ligands have been developed for cycloaddition reactions of CO₂ and epoxides. The results indicated that L1-NiBr₂, a promising candidate for commercial applications, showed excellent catalytic activity and substrate compatibility under co-catalyst-free and solvent-free conditions. As compared to the disubstituted one, most of the cyclic carbonates achieved high yields (>90%) and selectivity even at 80 °C under 1 atm CO₂ and 0.5 mol% of the catalyst, except the long aliphatic chain substituted one, suggesting that the large epoxide substrates restricted diffusion into the confined spaces of the catalyst. Besides, the developed catalyst has good recyclability and stability, which were further proved through ICP to test the catalyst leaching, TGA and IR spectra. Furthermore, mechanistic investigations followed by DFT suggested that Ni acted as a Lewis acid and its anion Br⁻ acted as a nucleophile to facilitate the ring opening.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We acknowledge the financial support of this work from the National Natural Science Foundation of China (22272094 and 21972079), Natural Science Foundation of Shandong Province (ZR2020QB034, ZR2019MB002 and ZR2023QB285) and Incubation Program of Youth Innovation in Shandong Province. Computer time was provided by the TAMU High-Performance Research Computing Facility, and software was provided by the Laboratory for Molecular Simulation.

Notes and references

1. (a) J. Rogelj, D. Huppmann, V. Krey, K. Riahi, L. Clarke, M. Gidden, Z. Nicholls and M. Meinshausen, Nature, 2019, 573, 357–363; (b) A. Modak, P. Bhanja, S. Dutta, B. Chowdhury and A. Bhaumik, Green Chem., 2020, 22, 4002–4033; (c) M. Thangamuthu, Q. Ruan, P. O. Ohemeng, B. Luo, D. Jing, R. Godin and J. Tang, Chem. Rev., 2022, 122, 11778–11829.
2. (a) F. Han, F. F. Xie, M. Y. Yin, L. H. Jing and P. Han, Org. Biomol. Chem., 2024, 22, 5724–5728; (b) M. He, Y. Sun and B. Han, Angew. Chem., Int. Ed., 2022, 134, e202112835; (c) Z. Q. Wang, C. H. Deng, X. Liu and W. M. Wang, Dalton Trans., 2023, 52, 11163–11167.
3. (a) A. Goeppert, M. Czaun, J.-P. Jones, G. K. S. Prakash and G. A. Olah, Chem. Soc. Rev., 2014, 43, 7995–8048; (b) Z. C. Zhang, A. Q. Guan, J. Y. Yu, X. D. Jiang, S. Han, Z. Y. Wen, B. Y. Du and B. Y. Song, New J. Chem., 2024, 48, 13245–13250; (c) Q. Zou, G. Long, T. Zhao and X. Hu, Green Chem., 2020, 22, 1134–1138.
4. (a) Z. C. Yang, J. L Ni, C. Y. Duan, Y. Feng and J. F. Yao, J. Mater. Chem., 2024, 12, 21279–21287; (b) Y. Yao, H. Zhang, C. Lu, H. Shang and Y. Tian, Eur. J. Org Chem., 2023, 26, e202300111.
5. (a) B. Schäffner, F. Schäffner, S. P. Verevkin and A. Börner, Chem. Rev., 2010, 110, 4554–4581; (b) W. Yu, E. Maynard, V. Chiaradia, M. C. Arno and A. P. Dove, Chem. Rev., 2021, 121, 10865–10907; (c) A. Centeno-Pedrazo, J. Perez-Arce, Z. Freixa, P. Ortiz and E. J. Garcia-Suarez, Ind. Eng. Chem. Res., 2023, 62, 3428–3443.
6. P. P. Pescarmona and M. Taherimehr, Catal. Sci. Technol., 2012, 2, 2169–2187.
7. (a) Y. A. Alassmy, Z. A. Pour and P. P. Pescarmona, ACS Sustainable Chem. Eng., 2020, 8, 7993–8003; (b) R. Jin, H. Xu, J. Easa, A. Chapero-Planell and C. P. O'Brien, J. Phys. Chem., 2023, 127, 1441–1454.
8. (a) B.-H. Xu, J.-Q. Wang, J. Sun, Y. Huang, J.-P. Zhang, X.-P. Zhang and S.-J. Zhang, Green Chem., 2015, 17, 108–122; (b) N. H. Kim, E. Y. Seong, J. H. Kim, S. H. Lee, K.-H. Ahn and E. J. Kang, J. CO₂ Util., 2019, 34, 516–521; (c) T. Chuasaard, M. Sinchow, N. Chiangraeng, P. Nimmanpipug and A. Rujiwatra, J. CO₂ Util., 2024, 80, 102686; (d) A. Rehman, F. Saleem, F. Javed, A. Ikhlaq, S. W. Ahmad and A. Harvey, J. Environ. Chem. Eng., 2021, 9, 105113–105140; (e) M. Navarro, A. Garcés, L. F. Sánchez-Barba, D. González-Lizana and A. Lara-Sánchez, Dalton Trans., 2023, 52, 6105–6116.
9. (a) E. M. Maya, M. González-Lucas and M. Iglesias, ChemistrySelect, 2017, 2, 9516–9522; (b) Z. Gao, L. Liang, X. Zhang, P. Xu and J. Sun, ACS Appl. Mater. Interfaces, 2021, 13, 61334–61345.
10. (a) Y. Liu, S. Wang, Z. Dai and Y. Xiong, Ind. Eng. Chem. Res., 2021, 60, 18218–18229; (b) Y. L. Hu, X. B. Liu and Q. Rong, Green Chem. Lett. Rev., 2023, 16, 2163192; (c) K. Guo, N. Ji, F. han, Q. Yang, N. Wang and C. Miao, RSC Sustainability, 2024, 2, 1074–1080.
11. (a) M. Aresta, A. Dibenedetto and A. Angelini, Chem. Rev., 2014, 114, 1709–1742; (b) C. K. Karan and M. Bhattacharjee, Inorg. Chem., 2018, 57, 4649–4656; (c) J. H. Kim, S. H. Lee, N. H. Kim and E. J. Kang, J. CO₂ Util., 2021, 50, 101595–101601; (d) M. Dolai, S. Biswas, E. Moreno-Pineda, W. Wernsdorfer, M. Ali, R. A. Alshgari, S. M. Wabaidur and A. Ghosh, Cryst. Growth Des., 2023, 23, 801–810.
12. M. H. Chisholm and Z. P. Zhou, J. Am. Chem. Soc., 2004, 126, 11030–11039.
13. (a) H. M. Hüppe, L. I. Mühlhaus, J. Heck, M. Eilers, H. Gildenast, S. Schönfeld, A. Dürrmann, A. Hoffmann, B. Weber, U. P. Apfel and S. H. Pawlis, Inorg. Chem., 2023, 62, 4435–4455; (b) M. Kourgiantaki, G. G. Bagkavou, H. I. Stathakis and A. L. Zografos, Org. Chem. Front., 2023, 10, 2095–2114; (c) B. Wang, X. Cao, L. Wang, X. Meng, Y. Wang and W. Sun, Inorg. Chem., 2024, 63, 9156–9163.
14. (a) B. Wang, L. Wang, J. Lin, C. Xia and W. Sun, ACS Catal., 2023, 13, 10386–10393; (b) J. E. Dengler, M. W. Lehenmeier, S. Klaus, C. E. Anderson, E. Herdtweck and B. Rieger, Eur. J. Inorg. Chem., 2011, 3, 336–343.
15. (a) M. Q. Xing, N. Liu, C. N. Dai and B. H Chen, Catalysts, 2024, 14, 370; (b) W. Moschkowitsch, S. Gonen, K. Dhaka, N. Zion, H. Honig, Y. Tsur, M. C. Toroker and L. Elbaz, Nanoscale, 2021, 13, 4576–4584.
16. (a) I. Zilbermann, E. Maimon, H. Cohen and D. Meyerstein, Chem. Rev., 2005, 105, 2609–2625; (b) J. Diccianni, Q. Lin and T. N. Diao, Acc. Chem. Res., 2020, 53, 906–919; (c) S. K. Kariofillis and A. G. Doyle, Acc. Chem. Res., 2021, 54, 988–1000; (d) B. H. Teng, Z. P. Bao, Y. Y. Zhao and X. F. Wu, Org. Lett., 2024, 26, 4779–4783.
17. (a) K. Takaishi, B. D. Nath, Y. Yamada, H. Kosugi and T. Ema, Angew. Chem., Int. Ed., 2019, 58, 9984–9988; (b) T. Nouri and M. Khorasani, J. Phys. Chem., 2024, 128, 166–176.
18. (a) M. Wu, B. Wang, S. Wang, C. Xia and W. Sun, Org. Lett., 2009, 11, 3622–3625; (b) S. Yu, C. Miao, D. Wang, S. Wang, C. Xia and W. Sun, J. Mol. Catal. A: Chem., 2012, 353–354, 185–191.
19. Y. A. Rulev, V. A. Larionov, A. V. Lokutova, M. A. Moskalenko, O. L. Lependina, V. I. Maleev, M. North and Y. N. Belokon, ChemSusChem, 2016, 9, 216–222.
20. Z. Alaji, E. Safaei and A. Wojtczak, New J. Chem., 2017, 41, 10121–10131.
21. (a) F. Chen, Q. Zhang, D. Wei, Q. Bu, B. Dai and N. Liu, J. Org. Chem., 2019, 84, 11407–11416; (b) R. Das and C. M. Nagaraja, Inorg. Chem., 2020, 59, 9765–9773; (c) S. Saltarini, N. V. Escobar, J. Martinez, C. G. Daniliuc, R. A. Matute, L. H. Gade and R. S. Rojas, Inorg. Chem., 2021, 60, 1172–1182.

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Footnotes

† Electronic supplementary information (ESI) available: Crystal information of L1-NiBr2, part screening reaction conditions, NMR data and spectra of ligands and products and computational methods. CCDC 2307070. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4su00556b

‡ These authors contributed equally.

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