Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Balancing between Heterogeneity and Reactivity in Porphyrin Chromium-Cobaltate Catalyzed Ring Expansion Carbonylation of Epoxide into β‑Lactone Senkuttuvan Rajendiran, Vinothkumar Ganesan, and Sungho Yoon* Department of Applied Chemistry, Kookmin University, 861-1, Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Republic of Korea
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S Supporting Information *
ABSTRACT: The synthesis of a unique heterogeneous catalyst that combines the functionality of a homogeneous catalyst and the advantages of a heterogeneous catalytic process is a continuing goal in various industrially applicable reactions. Here, we report heterogenization of homogeneous catalyst for lactone production from epoxide carbonylation through a facile polymerization using Friedel−Crafts reaction. A correlation between reactivity and degree of heterogeneity has been deduced by synthesizing different sized polymeric catalysts. The partially polymerized catalyst showed a remarkable initial turnover frequency of 400 h−1, and the fully polymerized catalyst displayed excellent selectivity during recycling with a total turnover number of 4100.
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INTRODUCTION The efficient transformation of epoxide into β-lactone has attracted considerable attention owing to its synthetic significance in the production of acrylic acid,1 β-hydroxyacids,2 β-hydroxyester,3−8 succinic anhydride,9,10 and biodegradable poly(β-hydroxybutyrate).11−14 Realizing the industrial importance of β-lactones, a number of homogeneous catalysts have been reported for the conversion of epoxide into a lactone.15−17 Among them, Coates et al. established that the well-defined homogeneous bimetallic complex tetraphenylporphyrin chromium tetracarbonyl cobaltate [TPPCr][Co(CO)4] exhibited excellent conversion of epoxides to lactones, which is the best catalyst to date for epoxide carbonylation. Moreover, these bimetallic complexes demonstrated the necessity of active ion pair for efficient carbonylation and gave important mechanistic insights (Scheme 1).18,19 In addition, these studies have received a great interest in commercial grounds. In an industrial point of view, however, heterogeneous catalytic systems are much desirable due to easy product
separation and catalyst recyclability. To this end, the search for developing methods to heterogenize the highly active catalysts is continuing. In this context, incorporation of active homogeneous centers onto supporting materials inevitably limits the amount of the active ion pair because of the steric restriction of the supports, which results in reduced epoxide carbonylation.20,21 Although, a recently developed Cr-MIL-101 supported heterogeneous catalyst possesses an active ion pair, it shows moderate activity compared to any homogeneous catalyst reported thus far.22 Therefore, to attain higher reactivity, heterogenization of active homogeneous catalysts such as [TPPCr][Co(CO)4] is expected to maintain their active ion-pair centers in them. In designing such an efficient heterogenization method, we focused our attention to systematically heterogenize the active homogeneous complex with the active centers intact using a well-known Friedel−Crafts polymerization method. Herein, the synthesis of chromium-cobaltate porphyrin organic polymer with remarkable catalytic activity and high selectivity toward epoxide carbonylation, which are comparable to the performance of homogeneous catalyst, is reported. In addition, one of the polymerized catalysts in the early period exhibits high dispersibility in solution, which could enable it to be used as a potential alternative for the homogeneous catalyst. The synthesized recyclable heterogeneous catalyst maintained 95% lactone selectivity in repeated cycles, demonstrating the excellent stability of the catalyst.
Scheme 1. Proposed Mechanism of Epoxide Carbonylation to Lactone
Received: December 3, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Scheme 2. A Schematic Representation of Polymerized Tetraphenylporphyrin Chromium-Cobaltate Complex
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RESULTS AND DISCUSSION The porous porphyrin was synthesized through the knitting strategy in which dimethoxymethane (DMM) was employed as a cross-linker to combine the phenyl ring of porphyrins with a methylene (−CH2−) bridge through the FeCl3 catalyzed Friedel−Crafts alkylation at 80 °C (Scheme 2).23 The progress of the reaction was monitored visually as well as by UV−visible spectroscopy (Figure 1). After the addition of a linker, over the reaction time, a typical sharp absorption band of metalloporphyrin undergoes a Soret shift from 448 to 454 nm (solid
red line). Notably, the presence of a typical and well-known porphyrin methyl cations peak in the near-IR region (Figure 1, inset, red solid line) possibly demonstrates the generation of intermediate carbocation during the Friedel−Crafts alkylation in Scheme 2. The observation of this absorption band over the reaction time affirms the continuous generation of a cationic intermediate for the multiconnection of the [TPPCr]Cl methyl linker to form a heterogeneous material. This result is in agreement with the mechanistic explanation of Li et al. and Tan et al., and also consistent with near-IR studies of other carbocation results.24−27 As the reaction proceeds to the completion, the observed peaks slowly diminish (solid black line) due to the formation of methylene bridges between the phenyl rings of the porphyrin polymers. It is worth to mention here that the visually observed gradual color changes of solution from reddish-orange to brown, which finally turned to almost colorless with the black precipitate formation, reveals the completion of heterogenization process. To further deepen the understanding of the heterogenization process, the catalyst was synthesized by varying the reaction time (3, 6, 12, and 24 h) (Scheme 2). The resultant precipitates were washed with water, THF, and diethyl ether to obtain a porous organic polymer porphyrin chromium chloride and are represented as POP-[TPPCr]Cl-3h (1), POP[TPPCr]Cl-6h (2), POP-[TPPCr]Cl-12h (3), and POP[TPPCr]Cl-24h (4), respectively. The morphology of the resulting precipitates was analyzed by scanning electron microscopy (SEM), and the results show irregularly shaped particles for 1, 2, and 3 and partially spherical particles for 4 (Figure 2). Particle size increased from 1 [>0.5 (10) μm] through to 3 [>1.2 (10) μm]. These morphological changes indicate the continuous linkage of the porphyrin unit to generate the connected oligomeric to
Figure 1. UV−visible spectra at different time intervals during the reaction of TPPCrCl with DMM and FeCl3 in 1,2-dichloroethane (DCE). (For clear representation, in the inset, we displayed the intermediate cation peak in higher concentration.) B
DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
dispersive X-ray (EDX) analysis demonstrates the presence of Co ions throughout the samples. FTIR spectra showed a CO stretching peak at 1875 cm−1 that further confirms the exchanged Co(CO)4 ion in 5, 6, 7, and 8 (Figure S2). Although this anion exchange reduces the surface area of the catalyst to 45, 66, 186, and 306 m2 g−1, respectively (Figure S7), the existence of porous channels is beneficial for mass transfer of substrates to the active sites (Figure S8 and Table S2). Further, the anion exchanged polymers show shifted Cr binding energies in XPS measurements and the corresponding cobalt ion peaks at 797.3 and 781.6 eV (Figure S9) are precisely matched with the homogeneous [TPPCr][Co(CO)4] complex. The Cr/Co contents in 5, 6, 7, and 8 were measured using ICP-OES and were found to be 3.46/3.61, 4.01/3.89, 3.36/3.51, and 3.16/3.11 wt %, respectively. All the data acquired from the structural characterization of 5, 6, 7, and 8 lead to performing carbonylation using propylene oxide (PO) (less toxic than ethylene oxide) in ether solvent (DME, which has been reported to be the best solvent for carbonylation of an epoxide into lactone) at 60 °C under 6.0 MPa of CO; the results are summarized in Table 1. To
Figure 2. Scanning electron microscopic images of 1, 2, 3, and 4.
polymeric structures, which is consistent with the UV−visible kinetic studies. The dispersion of different sized materials 1, 2, 3, and 4 was examined by absorption analysis (Figure S1). These particles remained dispersed in the solution which settles down at a different time interval (30, 26, 22, and 16 min), indicating the facile separation of the catalyst (Figure S1). The structural integrity of the polymeric materials was initially assessed by Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra of 1, 2, 3, and 4 reveal a weak signal of the methylene linker at around 2910−2980 cm−1 indicative of successful polymerization (Figure S2).23 Furthermore, a sharp peak at 1000 cm−1 confirms the presence of Cr-porphyrin in the polymeric materials.28 X-ray photoelectron spectroscopic (XPS) analysis of 1, 2, 3, and 4 shows peaks at binding energies of 586.8 and 577 eV, which correspond to Cr 2p1/2 and 2p3/2 in a porphyrin (Figure S3). To understand the porosity of heterogenized porphyrins 1, 2, 3, and 4, nitrogen sorption experiments were measured at 77 K, and the result shows the surface area of 88, 129, 268, and 421 m2 g−1, respectively (Figure S4). The observed gradual increase in surface area of the samples indicates that the formed shorter polymeric chains rearranged themselves into a dense packing arrangement, which reduces the pore volume, resulting in the low surface area. In contrast, the growth of the polymeric chain increased dramatically with the reaction time, which hindered the arrangement of polymeric chains from close packing. This resulted in increased pore volume and thereby increasing the surface area for 4. In addition, the Barrett−Joyner−Halenda (BJH) plot shows the presence of mesopores in 1 and both micropores and mesopores in 2, 3, and 4 samples (Figure S5 and Table S1). Given the sufficient pore size in 1, 2, 3, and 4, endogenous anion (Cl−) exchange was performed with freshly prepared KCo(CO)4 at room temperature to form porous organic polymer porphyrin chromium cobalt tetracarbonyl complexes as a dark black solid and represented as POP-[TPPCr][Co(CO)4]-3h (5), POP-[TPPCr][Co(CO)4]-6h (6), POP[TPPCr][Co(CO) 4 ]-12h (7), and POP-[TPPCr][Co(CO)4]-24h (8), respectively (Scheme 2). The SEM images of the obtained black precipitates show no apparent changes in morphology (Figure S6), and the corresponding energy-
Table 1. Carbonylation of PO Using Catalysts 5, 6, 7, and 8a entry
catalyst
PO (equiv)
conversionb (%)
TOFc (h−1)
1 2 3 4 5
TPPCrCo(CO)4 5 6 7 8
2400 2400 2400 2400 2400
>99 92 75 56 43
530 400 300 180 120
a
Reaction performed in 2.5 mL of DME in a tube reactor pressurized with 6.0 MPa of CO at room temperature and heated to 60 °C for 24 h. bDetermined by 1H NMR spectroscopy with naphthalene as an internal standard. cTOF for first 1 h.
demonstrate the validity of our heterogeneous reaction system, epoxide carbonylation has been performed with previously reported [TPPCr][Co(CO)4] catalyst in DME, at 60 °C under 6.0 MPa of CO, resulting in 99% conversion to βbutyrolactone with a turnover number (TON) of 2400 (entry 1). This result encouraged us to evaluate the activity of 5 with the same condition of entry 1, showing 92% conversion of β-butyrolactone with the initial turnover frequency (TOF) of 400 h−1 (entry 2). Even though the catalyst 5 is in the beginning stage of heterogenization, it is soluble in reaction condition which enables great interaction of epoxide with Cr/Co centers, resulting in homogeneous catalyst like activity. In similar condition, the other catalysts were explored for PO carbonylation and found that 6, 7, and 8 showed conversion of 75, 56, and 42% with initial TOF of 300, 180, and 120 h−1 respectively (entries 3, 4, and 5). Although decreased activity was observed, it is the highest TOF reported to date than any other immobilized heterogeneous catalyst.20−22 This reducing activity trend is explainable because through the heterogenization process the catalyst behavior would deviate from the homogeneous catalyst and shows limited solubility with the substrate. The observed excellent selectivity of the lactone indicates that the process of heterogenization occurred by maintaining the bimetallic ion pair as like homogeneous catalyst [TPPCr][Co(CO)4]. Further, the stability of 8 was examined by hot-filtration C
DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry tests, and ICP-OES analysis of the filtrate shows no metal content was leached. At least five cycles of PO carbonylation were performed to investigate the stability of the catalysts 5, 6, 7, and 8. After the initial run, catalysts were easily separated from the reaction mixture by simple filtration and washed with DME for further use. ICP-OES analysis of the separated precipitate demonstrates that the ratio of Cr/Co was almost maintained for 7 and 8 (3.24/3.41 and 3.13/3.01 wt %), whereas those for 5 (3.12/ 2.35) and 6 (3.89/3.03) showed a reduced Cr/Co content. Since 5 demonstrates homogeneous catalyst characteristics, the shortly formed polymers are dispersible in reaction condition which undergoes dissociation easily. The recovered catalyst was subjected to further four runs; the overall activity of 7 and 8 was almost maintained (based on cobalt wt %), whereas 5 and 6 showed reduced activity (Figure 3 and Table S3). This decreased activity is due to the partial
The rate of PO carbonylation of catalysts 5, 6, 7, and 8 was studied through kinetic experiments, and the products were monitored by 1H NMR spectroscopy (Figure 4 and Table S4).
Figure 4. Kinetic study of β-butyrolactone formation with [TPPCr][Co(CO)4], 5, 6, 7, and 8.
Initially, [TPPCr][Co(CO)4] shows complete conversion in 12 h with initial TOF of 530 h−1. Similarly, catalyst 5 attained its full conversion in 16 h with an initial TOF of 400 h−1, and the conversion rate almost maintained with the homogeneous catalyst. However, in the case of 6, 7, and 8, the rate of conversion of PO to lactone is gradually reduced compared to [TPPCr][Co(CO)4], because the formed lactone is dispersed and bound with an available catalytic center that reduces the PO approach to the metal center which prolongs the reaction to complete. These results indicate that the highly soluble form of catalyst 5 exhibits a faster reaction rate than the fully heterogenized catalyst 8. After endured the complete activity and stability studies of 8 in batch-type reactions, this heterogeneous catalyst was subjected to a three-phase continuous process. A fixed bed reactor was packed with 8 in silicon carbide and pressurized with 2.0 MPa of CO at the flow rate of 30 mL/min, and subjected to a flow of 0.5 M PO in diethyl ether at 1.6 mL/h; β-butyrolactone was obtained with the initial TOF of 17 h−1 and TON of 100 in 12 h (Figure S10). It is noteworthy that this observed catalytic activity is the highest for epoxide carbonylation in both batch type20,21 and three-phase continuous reaction than any other modified heterogeneous catalyst under similar condition.22
Figure 3. Recyclability of catalysts 5, 6, 7, and 8 under reaction conditions of 60 °C and 6.0 MPa of CO. The 6th cycle represents epoxide carbonylation performed with a regenerated catalyst. Dotted line indicates the acetone formation during the recycle experiments.
solubility of the Cr part and rapid loss of Co ions from the framework, which was confirmed by the ICP-OES analysis (Cr/Co content 2.76/1.18 and 3.07/1.58 wt %). Notably, upon recycling, the relative amounts of acetone were generated (Table S3). To explore the possibility of replenishing the cobalt content of the recycled catalysts, after the fifth run, catalyst was separated and treated with freshly prepared K[Co(CO)4] in THF for 24 h (see procedures in Supporting Information) and Cr/Co content was analyzed by ICP-OES. In the case of 5 and 6, the Cr/Co ratio was not retained as like a fresh catalyst because this catalytic system partially lost its cationic sites which limit the regeneration of the catalyst. However, this partial regeneration did not limit the activity of the catalyst. Moreover, it demonstrates that these catalysts are superior to the homogeneous part. Further, PO carbonylation was performed with the regenerated catalyst under the similar conditions, resulting in the generation of β-butyrolactone (98% and 99%) for 7 and 8 (Figure 3); however, for 5 and 6, the conversion reached only 75% and 85%, respectively. Among the developed catalysts, shortly polymerized 5 showed reduced recyclability, whereas 8 maintained its overall activity with the total TON of 4100 (five cycles) which is an attractive heterogeneous catalyst for the large-scale production of lactone.
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CONCLUSION We bridged homogeneous catalytic function with the benefits of heterogeneous support through a direct knitting strategy using the Friedel−Crafts alkylation method. The active bimetallic ion-pair sites of the homogeneous complex was maintained through the heterogenization. This study has demonstrated the catalytic activity differences between partially polymerized and fully heterogenized catalysts in comparison with the homogeneous complex that is used for epoxide carbonylation. The partially heterogenized catalysts were highly dispersed in solution and displayed a comparable rate of epoxide carbonylation as like a homogeneous catalyst. On the other hand, fully heterogenized catalyst showed high stability, activity, recyclability, and reusability. Moreover, these catalytic studies have proven that this catalyst would be a possible candidate for large-scale production. D
DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
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Synthesis of POP-[TPPCr]Cl-24h (4). To a solution of TPPCrCl (0.2400 g, 0.3428 mmol) in DCE (10 mL), anhydrous FeCl3 (0.2224 g, 1.3712 mmol) and DMM (0.1043 g, 1.3718 mmol) were added in room temperature. The greenish-brown solution was stirred at 80 °C for 24 h and cooled to room temperature. The resulting black precipitate was filtered and washed with water (2 × 100 mL), DMF (50 mL), THF (50 mL), methanol (50 mL), acetonitrile (50 mL), acetone (50 mL), dichloromethane (50 mL), and ether (50 mL). The precipitate was further purified by a Soxhlet method with THF/ methanol (50/50 mL) and dried under vacuum at 60 °C for 24 h and obtained as a black powder (Yield = 0.2219 g). Synthesis of 5. In a glovebox, 1 (0.079 g) and KCo(CO)4 (0.4 g) were dissolved in 10 mL of THF and stirred at room temperature for 24 h. The reaction mixture was filtered, and the precipitates are washed with THF/diethyl ether (2/8) (2 × 10 mL) and pentane (10 mL). The resulting black precipitates was dried under vacuum for 16 h (Yield = 0.082 g). Synthesis of 6. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10 mL of THF was added to 2 (0.2080 g) and stirred at room temperature for 24 h. The reaction mixture was filtered, and the precipitates are washed with THF/diethyl ether (2/8) (2 × 10 mL) and pentane (10 mL). The resulting black precipitates were dried under vacuum for 16 h (Yield = 0.214 g). Synthesis of 7. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10 mL of THF was added to 3 (0.1864 g) and stirred at room temperature for 24 h. The reaction mixture was filtered, and the precipitates are washed with THF (10 mL), methanol (10 mL), and pentane (10 mL). The resulting black precipitates were dried under vacuum for 16 h (Yield = 0.195 g). Synthesis of 8. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10 mL of THF was added to 4 (0.2219 g) and stirred at room temperature for 24 h. The reaction mixture was filtered, and the precipitates are washed with THF (10 mL), methanol (10 mL), and pentane (10 mL). The resulting black precipitates were dried under vacuum for 16 h (Yield = 0.236 g). General Procedure for Epoxide Ring-Opening Carbonylation into β-Lactone in Batch Type. A 100 mL SS tube reactor was dried at 80 °C overnight and vacuumed for 4 h. In a glovebox, it was equipped with a stir bar and charged with 5 (0.0091 g, 0.0056 mmol of cobalt) (PO: 0.7851 g, 13.5362 mmol), 6 (0.0085 g, 0.0056 mmol of cobalt) (PO: 0.7902 g, 13.6241 mmol), 7 (0.0121 g, 0.0072 mmol of cobalt) (PO: 1.0184 g, 17.5586 mmol), and 8 (0.0106 g, 0.0056 mmol of cobalt) (PO: 0.7821 g, 13.4844 mmol) in 2.5 mL of dry DME. The reactor was taken out from the glovebox and immediately cooled to 0 °C and purged with 0.5 MPa of CO. Then the reactor was pressurized to 6.0 MPa of CO and heated to 60 °C for 24 h. After the reaction time, the reactor was cooled to 0 °C, and CO gas was slowly released inside the hood. The crude sample was weighed and dissolved in CDCl3, filtered through Celite, and washed with CDCl3. The conversion was calculated using 1H NMR spectroscopy with naphthalene as an internal standard. General Procedure for Epoxide Ring-Opening Carbonylation into β-Lactone in Three-Phase Continuous Reaction. In a glovebox, the 0.038 g of 8 with ∼0.3218 g of silicon carbide powder was mixed and the solid mixture was packed between two quartz wool plugs in a SS tubing segment (OD - 9.55 mm, ID - 7.08 mm, wall thickness 1.23 mm). A thermocouple probe was mounted downstream in direct contact with the middle of the catalyst bed for accurate temperature maintenance. Remaining space was filled with glass beads. Substrate 0.5 M PO in diethyl ether was charged into a 50 mL conical flask and sealed with an SS valve in the glovebox. The packed tubing segment and liquid feed conical flask were transferred from the glovebox. The catalyst was connected to the main heated and liquid feeder connected to a precalibrated liquid delivery HPLC pump (HKS 100) under a nitrogen atmosphere. The reactor was pressurized with a mass flow controller (Brooks Instruments, 5850E series) to 20 bar of CO using a back-pressure regulator (Tescom) and allowed to stabilize to the flow rate of 30 mL/min of CO at the desired temperature (75 °C for preheater to vaporize the substrate and 60 °C for catalyst main heater). After pressurized the reactor
EXPERIMENTS
General Considerations and Physical Measurements. All manipulations of air- and water-sensitive compounds were carried out in the glovebox. All the chemicals purchased were of analytical grade from Tokyo Chemical Industry and Sigma-Aldrich and were used as received unless mentioned otherwise. Tetrahydrofuran was refluxed over sodium/benzoquinone and distilled under a N2 atmosphere. MeOH was refluxed over Mg/I and distilled under a N2 atmosphere. PO and acetonitrile were distilled over calcium hydride under a N2 atmosphere. KCo(CO)4 was prepared by following reported procedure.8 All new compounds were fully characterized by standard spectroscopic techniques. Deuterated solvents were purchased from Cambridge Isotope Laboratories, Inc., and used as received. NMR spectra were recorded on a Bruker Advance IV (400 MHz) at 298 K, and chemical shifts were referenced to the TMS peak. IR spectra were collected on a Nicolet iS 50 (Thermo Fisher Scientific) spectrometer using attenuated total reflection (ATR) techniques. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were measured on a JEOL LTD (JAPAN) JEM-7610F operated at an accelerating voltage of 15.0 kV. N2 adsorption/desorption was measured at 77 K using an automated gas sorption system (Belsorp II mini, BEL Japan, Inc.). Chromium and cobalt content in complexes 5, 6, 7, and 8 was determined using Inductively coupled plasma optical emission spectroscopy (ICP-OES) (iCAP-Q, Thermo Fisher Scientific) using a microwave assisted acid system (MARS6, CEM/ USA). X-ray photoelectron spectroscopy (XPS) analysis was performed on an ESCA 2000 (VG Microtech) at a pressure of ∼3 × 10−9 mbar using Al Kα as the excitation source (hγ = 1486.6 eV) with the concentric hemispherical analyzer. Research-grade carbon monoxide was purchased from Sinyang Gas Company, Korea, with 99.995% purity used as received. All batch type carbonylation reactions were performed in a 100 mL stainless steel (SS) tube reactor and fitted with a pressure gauge and pressure release valve. Threephase continuous carbonylation was performed with a SS reactor. All carbonylation reactions were set up and run in a well-ventilated fume hood equipped with a carbon monoxide detector (see MSDS for proper handling of CO). PO conversion, β-butyrolactone was quantified by 1H NMR using naphthalene as an internal standard in CDCl3. Caution! Toxic chemical dicobaltoctacarbonyl and high pressured carbon monoxide gas were used in the work. Synthesis of POP-[TPPCr]Cl-3h (1). To a solution of TPPCrCl (0.1321 g, 0.1897 mmol) in DCE (10 mL), anhydrous FeCl3 (0.1226 g, 0.7558 mmol) and DMM (0.0575g, 0.7567 mmol) were added in room temperature. The greenish-brown solution was stirred at 80 °C for 3 h and cooled to room temperature. The resulting reddish-brown crude was quenched and washed with water (2 × 100 mL), dichloromethane (2 × 50 mL), and diethyl ether (2 × 50 mL). The precipitates were dissolved in THF (200 mL), all solvents were removed, and the resultant was dried under vacuum at 60 °C for 24 h. The black precipitates were soluble in THF (Yield = 0.079 g). Synthesis of POP-[TPPCr]Cl-6h (2). To a solution of TPPCrCl (0.2419 g, 0.1897 mmol) in DCE (10 mL), anhydrous FeCl3 (0.2246 g, 1.3858 mmol) and DMM (0.1104 g, 1.4546 mmol) were added in room temperature. The greenish-brown solution was stirred at 80 °C for 6 h and cooled to room temperature. The resulting reddish-brown crude was quenched and washed with water (2 × 100 mL) and THF/ pentane (5/95) (50 mL), dichloromethane (2 × 50 mL), and diethyl ether (2 × 50 mL), and dried under vacuum at 60 °C for 24 h. The black precipitates were soluble in hot THF (Yield = 0.208 g). Synthesis of POP-[TPPCr]Cl-12h (3). To a solution of TPPCrCl (0.2065 g, 0.2954 mmol) in DCE (10 mL), anhydrous FeCl3 (0.1916 g, 1.1832 mmol) and DMM (0.090 g, 1.1816 mmol) were added in room temperature. The greenish-brown solution was stirred at 80 °C for 12 h and cooled to room temperature. The resulting crude was quenched and washed with water (2 × 100 mL), THF (100 mL), methanol (50 mL), diethyl ether (50 mL), and pentane (50 mL), and dried under vacuum at 60 °C for 24 h. The black precipitates were partly soluble in hot methanol (Yield = 0.1864 g). E
DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry setup, begin the substrate flow rate of 1.6 mL/h to the preheater section under CO atmosphere. Upon continuous flow of substrate and CO flow, every 1 h time interval β-butyrolactone was collected and weighed. The conversion was calculated using 1H NMR spectroscopy with using naphthalene as an internal standard in CDCl3.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03361.
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Experimental details, 1H NMR, XPS, BET, UV−visible, and FTIR analysis, SEM-images, and EDS mapping (PDF)
AUTHOR INFORMATION
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*E-mail:
[email protected]. ORCID
Senkuttuvan Rajendiran: 0000-0002-7335-2053 Sungho Yoon: 0000-0003-4521-2958 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We acknowledged financial support by the C1 Gas Refinery Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2018M3D3A1A01018006).
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REFERENCES
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DOI: 10.1021/acs.inorgchem.8b03361 Inorg. Chem. XXXX, XXX, XXX−XXX
