Highly Stable Chiral ZirconiumâMetallosalen Frameworks for CO2

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Energy, Environmental, and Catalysis Applications

Highly Stable Chiral Zirconium-Metallosalen Frameworks for CO2 Conversion and Asymmetric C-H Azidation Jiawei Li, Yanwei Ren, Chenglong Yue, Yamei Fan, Chaorong Qi, and Huanfeng Jiang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b14118 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on September 27, 2018

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ACS Applied Materials & Interfaces

Highly Stable Chiral Zirconium-Metallosalen Frameworks for CO2 Conversion and Asymmetric C-H Azidation Jiawei Li, Yanwei Ren*, Chenglong Yue, Yamei Fan, Chaorong Qi and Huanfeng Jiang* Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 510641, P. R. China.

ABSTRACT: The engineering of highly stable metal-organic frameworks (MOFs) will unveil the intrinsic potential of these materials for practical applications, especially for heterogeneous catalyses. However, it is fairly challenging to rationally design robust MOFs serving as highly effective and reusable heterogeneous catalysts. Here, for the first time, we report the construction of four robust UiO-type chiral zirconium-metallosalen frameworks, denoted as ZSF-1~4. Single crystal X-ray-diffraction reveals that the frameworks consist of twelve-connected Zr6O8 clusters with privileged chiral metallosalen ligands anchored at ideal positions, generating confined chiral cages that enable synergistic activation. Unlike UiO-68 that is highly sensitive to aqueous solutions, ZSF-1~4 exhibit excellent chemical stability in aqueous solutions with a wide range of pH owing to the abundant hydrophobic groups within metallosalen ligands. These features render ZSF-1 and ZSF-2 to be an excellent recycled heterogeneous catalyst for the conversion of imitated industrial CO2 with epoxides into cyclic carbonates with the highest reported turnover numbers in Zr-MOFs. With regard to asymmetric catalysis, ZSF-3 and ZSF-4 can effectively catalyze C-H azidation reaction in water-medium with ee value up to 94%. Moreover, these robust ZSFs can be further extended to other analogues with various metal centers through demetallization-remetallization strategy, which renders them to be excellent platform for broader field. Keywords: zirconium-based metal-organic framework, chiral metallosalen, chemical stability, hydrophobic character, CO2 conversion, asymmetric C-H azidation

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

INTRODUCTION Chiral metallosalen complexes have won profound reputation as outstanding homogeneous catalysts for various asymmetric catalyses such as epoxidation of olefins1, hydrolytic kinetic resolution2, olefin aziridination3, cyclopropanation4, cyanosilylation5, aminolysis of epoxides6 and so on. However, because of the separation difficult from reaction mixture and the existence of intermolecular deactivation pathways, these privileged catalysts have limitations in recycling. Accordingly, researchers in recent years have devoted much effort to construct the recyclable salen-based catalysts via heterogenization into crystalline porous materials such as metal-organic frameworks (MOFs)7-16 and covalent organic frameworks (COFs).17, 18 Among them, the modular nature of MOFs derived from the rational combination of various chiral metallosalen ligands and metal nodes endows adjustable porosity, tunable catalytic performances and designable topology. In addition, the collaborative microenvironment and/or framework confinement effect of MOFs can not only effectively enhance the catalytic performances, but also improve the lifetime through eliminating intermolecular deactivation pathway. Besides, MOFs tend to take the highly ordered crystal structures that can be easily characterized by single crystal X-ray crystallography (SCXRD), which is benefit for their structure-property relationship elucidation. Although MOFs have shown superior talent in heterogeneous catalysis, the chemical (more specifically, hydrolytic) and thermal stabilities are important for industrial uses in many catalytic processes for which varying pH, the presence of water vapor and high temperatures are common. As a result, there is a strong need to develop highly stable MOFs for efficient asymmetric catalysis, which is challenging in synthetic chemistry and material science. To date, several strategies for circumventing the vulnerability of MOFs have been created to develop robust MOFs such as MIL19, UiO20 and ZIF21 series, which are composed of either carboxylate ligands with high-oxidation metal clusters22-28 or azolate-containing linkers with divalent metals29. Among them, UiO-type MOFs, especially UiO-66 compounds, which consisted of twelve-connected Zr6O8 nodes and various terephthalic acid derivatives, were found to be highly stable in water and acidic solutions owing to the strong zirconium-oxygen bonds (Zr-O bond energy: 776 kJ mol-1) and higher linker-node connectivity. This superiority results in various utilities of UiO-66 analogues in water-involved applications. However, UiO-type MOFs become 2


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vulnerable to water and alkaline solutions when elongated carboxylate linkers were used. This phenomenon roots in the intrinsic stronger interaction between zirconium and oxygen from water or base than from carboxylate linkers, as revealed by the natural bond orbital (NBO) theory.30 Further, bulky linkers point to framework with larger openings, which permits the attack of clustering water molecules to Zr-O bonds, leading to more fragile frameworks, as in the cases of UiO-67 and UiO-68. As a consequence, reports on the utilization of extended isoreticular UiO derivatives are far more limited, though their larger openings are preferable in many applications. Herein, we disclose the construction of a new series of chiral UiO-type zirconium-metallosalen frameworks (ZSFs, Scheme 1) based on twelve-connected Zr6O4(OH)4 nodes and tunable metallosalen-derived dicarboxylic ligands. The design strategy is based on the following considerations: (1) the intrinsic robust Zr-O bond can render the framework high thermal stability; (2) incorporation of various hydrophobic groups on the metallosalen linker can enhance the moisture resistance of the corresponding ZSFs; (3) the rich coordination chemistry of the salen core enables the chelating of different metal center for various organic transformations; and (4) the metallosalen can be facilely incorporated with different chiral groups which can contribute to enantioselective catalyses. Assembled from chiral ditopic metallosalen ligands and ZrCl4, ZSFs feature fcu topology and exhibit high water endurance due to the hydrophobicity of tert-butyl, cyclohexane and phenyl groups from metallosalen ligands, which make them be promising heterogeneous catalysts in various water-involved organic transformations. Additionally, through a demetallization-remetallization strategy, the metal center of metallosalen of ZSFs can be facilely tuned and extended to Cu2+, Fe3+ and Ti4+, which endows these robust ZSFs outstanding catalytic platform for more abundant organic transformations.

Ph

Cy-salen-Ni N

N Ni

HOOC

O t

COOH

HOOC

But

O t

But

Ph

Ph

O Bu

COOH

+

N

N Mn

O Cl

t

Zr6O4(OH)4

Ph-salen-Mn

N Mn

HOOC

O

Bu

Cy-salen-Mn N

Ph-salen-Ni

N Ni

O

Bu

Ph

N

≡

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


COOH

HOOC

O

O

COOH

≡

Cl But

t

Bu

ZSF-1~4

But

Scheme 1. Synthesis of ZSFs from metallosalen ligands.

3



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RESULTS AND DISCUSSION Synthesis and Characterizations One main obstacle in the preparation of zirconium-based MOFs (Zr-MOFs) is the fast precipitation between the oxophile zirconium cation and the carboxylate oxygen anion. This conundrum makes the synthesis of Zr-MOFs highly irreproducible and uncontrollable. The modulation approach, initially developed by Kitagawa’s group,31,

32

has been employed

tremendously to tune the crystallinity, particle size, morphology, porosity, defects and stability of the resulting MOFs. Generally, modulators are conceived to compete with the linkers for metal cation, thus kinetically regulating the nucleation rate, which in turn controls the crystal growth process. In 2011, with benzoic acid as the modulator, Behrens et al. successfully prepared the first UiO-type MOF that can be determined by SCXRD.33 Since then, researchers have focused on achieving single crystals of Zr-MOFs suitable for X-ray determination through the precise screening of the modulators. Notwithstanding, the synthesis of X-ray-quality single crystals of Zr-MOFs is a trial and error enterprise and most of these compounds are still resolved by powder X-ray-diffractions (PXRD), which is unfavorable for their structure-property relationship elucidation and function adjustments. The synthesis of the X-ray-quality single crystals of ZSF-1 is a long-term trial, in which various modulators have been examined. Initial tests were conducted by dissolving the mixture of ZrCl4, Cy-salen-Ni and modulators (benzoic acid, acetic acid or formic acid) in DMF and stored at 120 o

C for 3 days. Unfortunately, all these three modulators (benzoic acid up to 240 eq., acetic acid up

to 162 eq. and formic acid up to 144 eq. relative to ligand) cannot tune the synthesis sufficiently, resulting in some unknown amorphous samples as indicated by PXRD. Considering the competitive relation between modulator and ligand, we envisaged that modulators with higher acidity might further reduce the number of nucleation sites, thus slowing down the reaction and facilitating the crystals growth. Therefore, we adopted trifluoroacetic acid (TFA) because the pKa value (0.3) of TFA is obviously lower than acetic acid (4.76), benzoic acid (4.21) and formic acid (3.74). On the other hand, recent study[34] reported that additional TFA modulator can help to increase crystal quality of mesoporous Zr based MOFs by eliminating a secondary phase forming in earlier crystallization step. The attempts were conducted by mixing ZrCl4, Cy-salen-Ni and TFA 4


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in DMF at 120 oC for 3 days. With the addition of up to 20 eq. TFA, the amorphous sample is still formed as judged by PXRD (Figure S1). Meanwhile, the corresponding scanning electron microscopy (SEM) images show irregular spherical particles (Figure 1). Further increasing the amount of TFA to 30 eq. lead to two broadened reflections on the background as seen in the PXRD patterns (Figure S1), which indicates the presence of the crystalline phases among the amorphous samples. With the addition of 50 eq. TFA, a full set of peaks of the crystalline phase can be discerned in the PXRD (Figure S1), indicating the complete detection of the pure crystalline materials. As shown in Figure 1, octahedral-shaped particles are appeared with clear edge, although in agglomeration form. When the amount of TFA is increased from 50 to 70 eq. and further to 110 eq., the degree of agglomeration decreases apparently and individual crystals are formed with a size of 10 µm, accompanying with the decrease of yield from 81% to 54% and 32%, respectively. Moreover, single crystals suitable for X-ray analysis can be found on the wall of the vial under this reaction condition. Replacing Cy-salen-Ni with other three linkers under the identical reaction condition will lead to the same octahedral-shaped crystals of ZSF-2~4. Although the X-ray-quality single crystals of ZSF-2~4 are not detected in these cases, their crystallinity and morphology are definitely confirmed through PXRD and SEM (Figures 3 and S2). These endeavors in the preparation of ZSF-1~4 suggest the acidity and amount of modulator as the determined role in regulating the crystallinity, morphology and particle size of Zr-MOFs.

Figure 1. Crystal growth of ZMF-1 modulated by TFA.

SCXRD analysis reveals that ZSF-1 crystallizes in chiral space group F432, and features fcu topology as UiO-68, in which Zr6O8 clusters are connected by twelve metallosalen linkers, 5



forming the basic secondary building unit (SBU) Zr6O4(OH)4(metallosalen)6 (Figure 2). The infinite extension between Zr6O8 clusters and metallosalen generates the ultimate 3D network. Due to the partial disorder of the metallosalen linker, the tert-butyl groups are crystallographic hard to be determined, and this makes the accurate estimation of the pore sizes of the network very difficult. This phenomenon is not uncommon in the refinement of many Zr-MOFs crystal structures. Figure 2 display one of the disordered structures with the occupancy of 50%. The structure involves two kinds of cages: a tetrahedral cage with a free aperture of ca. 12.4 Å and an octahedral cage with a free aperture of ca. 17.6 Å, both of which are accessible by the triangular windows with side lengths of ca. 13.6 Å. PLATON calculation reveals a large solvent-accessible volume of 19543 Å 3 (61.06% of cell), which is very beneficial to guest accommodation. The incorporation of metallosalen ligand endows these cages with chiral source that have the potential for chiral recognition and enantioselective catalysis. Intriguingly, the faces of six metallosalen ligands are well oriented to the tetrahedral cages with an average distance of 8 Å between the active metal centers, which facilitates the synergistic activation of guest molecules (Figure S3). This compelling structural feature makes ZSFs very attractive to heterogeneous catalysis.

Figure 2. Top left: view of the 3D network of ZSF-1; Top right: Zr6O4(OH)4(COO)12 SBU; Bottom left: tetrahedral cage; Bottom right: octahedral cage.

Thermogravimetry analyses (TGA) were conducted to evaluate the thermal stabilities of ZSF-1~4, and the TG curves implied that ZSF-1~4 could maintain their framework until 430 oC 6


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(Figure S4). The X-ray photoelectron spectroscopy (XPS) was then conducted to confirm the oxidation states of the metal centers in ZSF-1~4 (Figure S5). The peaks of Ni 2p3/2 at 854.28 eV, Ni 2p1/2 at 871.58 eV of ZSF-1 and Ni 2p3/2 at 854.24 eV, Ni 2p1/2 at 871.47 eV of ZSF-2 indicate that the oxidation state of the nickel species remains +2.35 While the Mn 2p2/3 peaks for ZSF-3 and ZSF-4 are at 641.78 and 641.68 eV, together with the Mn 2p1/2 peaks at 653.18 and 652.99 eV, respectively, suggesting that the oxidation state of Mn ions are +3.35 Moreover, the ratio between Zr and transition metal in the ligands of ZSF-1~4 are determined by Inductively coupled plasma optical emission spectrometry (ICP-OES), which indicate the ratios of 1: 0.98, 1.02, 1.03 and 0.97, respectively. The solid-state circular dichroism (CD) spectra indicate that ZSF-1~4 made from R and S enantiomers of the salen linkers are mirror images of each other, demonstrating their enantiomeric nature (Figure S7). The Ar adsorption measurements were conducted at 87 K to confirm the permanent porosity of ZSF-1~4. As shown in Figure S8, the isotherms of ZSF-1~4 all present

type

I

behavior,

indicative

of

microporous

materials.

The

apparent

Brunauer-Emmett-Teller (BET) surface areas calculated are 419/422 m2/g for ZSF-1/ZSF-3, and 355/359 m2/g for ZSF-2/ZSF-4, respectively, which are obviously lower than that of UiO-68 due to the introduction of abundant bulky groups and metal cations on the linkers. Besides, the reduced BET surface areas of ZSF-2 (ZSF-4) compared to ZSF-1 (ZSF-3) can be ascribed to the more bulky diphenyl groups than cyclohexane groups. This phenomenon can also be ascertained from the DFT pore size distributions. For ZSF-1 (ZSF-3) with cyclohexane groups, the diameter of the octahedral pore changes from 17.7 to 15.2 Å, while ZSF-2 (ZSF-4) with diphenyl groups leads to dramatic decrease of the diameter of the octahedral pore to 11.9 Å (Figure S8). Unsaturated coordinative metal sites are highly responsible for the interaction of frameworks with CO2. In view of the different metal sites in metallosalen, we evaluated the CO2 adsorption isotherms of ZSF-1~4 at 273 K and 298 K (Figure S8). For ZSF-1 and ZSF-2 with Ni sites, the CO2 adsorption capacities at 298 K and 1 atm are 23.78 and 22.97 cm3/g respectively, which then increased to 40.87 and 37.79 cm3/g at 273 K. As for ZSF-3 and ZSF-4, the CO2 adsorption capacities at 298 K and 1 atm are 24.17 and 23.67 cm3/g, which increased to 43.74 and 41.17 cm3/g at 273 K, respectively. These values are comparable to those of previous reported metallosalen-based MOFs.7 The isosteric heats of adsorption (Qst) are calculated using Clausius-Clapeyron equation to gain more insights into the intrinsic CO2 adsorption capacity of 7



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ZSF-1~4 (Figure S9). The Qst values at low coverage are calculated to be 40.54, 39.19, 42.25 and 39.77 kJ/mol, respectively. These high Qst values suggest strong interactions of CO2 with ZSF-1~4, highlighting their potential usages in CO2 involved applications. (a)

(b) As-synthezied ZMF-4 pH = 10

As-synthezied ZMF-3 pH = 9

As-synthezied ZMF-2 pH = 0

As-synthezied ZMF-1

o

100 C H2O

Simulated pattern of ZMF-1 from CIF

H2O Pristine

UiO-68 5

10

15

20

25

5

30

2 theta/degree

(c)

10

15

20

25

30

2 theta/degree

(d) pH = 11

Acetone pH = 10

Toluene pH = 0

Methanol o

100 C H2O

ethyl acetate dichloromethane

H2O

tetrahydrofuran Pristine

5

10

15

20

25

Pristine

30

5

2 theta/degree

10

15

20

25

30

2 theta/degree

Figure 3. PXRD patterns of ZSF-1~4 (a); ZSF-1 in aqueous solutions (b); ZSF-2 in aqueous solutions (c); and ZSF-1 in various organic solvents (d).

Chemical Stability As expected, due to the existence of hydrophobic groups, ZSF-1~4 show apparently improved stability in aqueous solution compared to UiO-68, although the metallosalen ligands possess similar lengths with TPDC (TPDC = terphenyl-4,4’’-dicarboxylicacid) used for UiO-68. The samples of ZSF-1~4 can maintain their cystallinity in aqueous solution for 24 h, while UiO-68 is highly sensitive to water (Figures 3 and S10). Moreover, boiling water also does not disturb the structure integrity of ZSF-1~4 as confirmed by PXRD patterns and Ar adsorption/desorption isotherms (Figures 3, S8 and S10). Macroscopical photos showed that the samples of ZSF-1~4 are readily floated on water (Figure S12), unambiguously suggesting their hydrophobic features. When it comes to the base-resistance of these compounds, the situation differs for ZSF-1/ZSF-3 and ZSF-2/ZSF-4. The compounds with diphenyl groups can sustain their structural integrity from 8


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pH = 0 to 10 for 24 h, while the others with cyclohexane groups lose their crystallinity at pH = 10 (Figure S9). The water contact angle experiments of ZSF-1~4 provide reasoned insight for this phenomenon. As can be seen from Figure 4, the contact angles for ZSF-1 (108o) and ZSF-3 (107o) are obviously lower than ZSF-2 (134o) and ZSF-4 (133o), indicating the increased hydrophobicity of the corresponding MOFs. This difference stems from the stronger hydrophobic capacity of diphenyl than cyclohexane groups, which sufficiently lower the “effective concentration” of OHentering into the cavities, thus rendering more robust frameworks towards base. Likewise, the Ar adsorption/desorption isotherms of the acid-/base-treated samples remained almost unaltered with the pristine samples, suggesting the porosity of ZSF-1~4 are well maintained (Figure S8). All these results above demonstrated that the hydrophobic metallosalen ligands exert a crucial role on the water-resistance of the corresponding Zr-MOFs. Apart from the water stability, the stablity of MOFs in organic solvent is also of great importance to their usages in various fields. As shown in Figures 2d and S11, ZSF-1~4 maintain their PXRD patterns after exposure to a variety of common organic solvents such as tetrahydrofuran, dichloromethane, ethyl acetate, methanol, toluene and acetone. Therefore, the strategy here by integrating the Zr6O8 clusters with higher linker-node connectivity and chiral metallosalen ligands with hydrophobic groups offers a facile route to develop highly stable MOFs that may have potential utilities in various fields involving common organic solvents or aqueous solutions with a wide pH range.

108o

134o

107o

133o

Figure 4. Macroscopical photos and contact angles of ZSF-1~4.

Cycloaddition of CO2 with Epoxides CO2 chemical fixation serves as a promising method to transform the worldwide excess CO2 to 9



value-added products. The cycloaddition of CO2 with epoxides is not only a 100% atom-economical route for cyclic carbonates which are widely used as precursors for polymeric materials, electrolytes for lithium-batteries and intermediates for fine chemicals, but also develops an environmentally favored process with CO2 as a nonflammable, nontoxic and sustainable C1 feedstock. The highly porous character of MOFs, together with their open metal sites, provides a unique platform to realize the CO2 capture and chemical fixation in a one-pot process. So far, a variety of MOFs have shown their excellent activity in catalyzing the cycloaddition of CO2 with epoxides.9, 36-43 Note that most of these cases involve the use of high-pure CO2 which are obtained through separation and purification from the flue mixed gases, causing extra time and energy costs. In fact, the raw flue gases usually contain water vapor and other acidic gases which could be detrimental to the framework integrity and catalytic activity of these MOFs. Therefore, finding a robust and recyclable material that can maintain its high-efficiency for the direct industrial CO2 chemical fixation is highly desirable and profitable for practical applications. We and others have reported various Ni2+-based MOFs as highly efficient and recyclable heterogeneous catalysts for the synthesis of cyclic carbonates from CO2 and epoxides, and proved that Ni2+ ion is effective Lewis acidic site for this reaction.11, 44-47 As aforementioned, ZSF-1 possesses tetrahedral cages composed of salen-Ni moieties, which enables the substrate and CO2 to be entrapped and synergistic Lewis acidic activated, generating an ideal nanoreactor. More importantly, ZSF-1 is proved to be stable towards aqueous solutions with a wide pH range. This character makes ZSF-1 very promising candidate for the direct industrial CO2 chemical fixation. As a result, we seek to explore the catalytic performances of ZSF-1 in this reaction. The catalyst was fully activated before the attempt. Initially, styrene oxide was selected as the model substrate to investigate the effects of different variables. The optimal reaction conditions involve 4 mmol epoxide, 1 atm CO2, 0.025 mol% ZSF-1, 0.25 mol% tetrabutylammonium bromide (TBAB), 100 o

C and 20 h. Similar to previous report,40 TBAB is proposed to be responsible for the ring-opening

process of epoxides and is indispensable for this reaction (Table 1, entry 2). The combination of TBAB and ZSF-1 showed the best catalytic result, giving 94% yield of the resulting cyclic carbonate at a low catalyst loading (Table 1, entry 5). For comparison, replacing ZSF-1 with the ligand Cy-salen-Ni species with ten times of catalyst loading only gives a yield of 61% (Table 1, entry 6). This discrepancy between ZSF-1 and Cy-salen-Ni is partly because of the low solubility 10


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of the molecular catalyst under the solvent-free conditions, limiting the fully utilization of its active site. On the other hand, the porous structure of ZSF-1 offers facile accessibility of the substrate to its inner active sites and the well-defined catalytic environment enables synergistic activation of the substrate by a couple of Ni2+ centers at one time. Consequently, the catalyst loading of ZSF-1 for this reaction can be as low as 0.025 mol%, resulting in very high turnover numbers (TON) which are the highest value of reported Zr-MOFs. The flue gases generally contain 76-77% N2, 12.5-12.8% CO2, 6.2% H2O, 4.4% N2 and certain amounts of acidic gases (SO2, NOx).48 Considering most MOFs stay structurally intact to N2 and O2, water vapor and acidic gases may be the most possible adverse factors to the framework integrity. Thus, H2O and acidic SO2 were introduced to the system to evaluate the catalytic performance and general reusability of ZSF-1. In a typical trial, 0.1 mL H2O was firstly added to the reaction. As H2O can immediately turn into water vapor in this system (100 oC), this operation serves as an imitation of the mixed gas of CO2 and H2O. Impressively, the catalytic performance of ZSF-1 was not affected by the addition of H2O (Table 1, entry 7), and its structural integrity was also well preserved (Figure S19). Furthermore, a mixed gas of SO2 (1 atm), CO2 (1 atm) and H2O was introduced to the catalytic system. Likewise, the mixed gases showed negligible influence to this reaction with a 91% yield of the resulting cyclic carbonate (Table 1, entry 8). The PXRD pattern of ZSF-1 under this reaction conditions also remained unchanged, suggesting the maintenance of cystallinity. The general reusability of catalyst is a key standard to evaluate whether it can be applied to practical applications. Therefore, we turn to investigate the recyclability of ZSF-1 under this reaction condition. The results implied that ZSF-1 could be reused for five times without apparent lose of activity under a mixed gases of SO2, CO2 and H2O (Table 1, entries 9-12). Again, the PXRD pattern of ZSF-1 after fifth-cycle experiment is identical to the as-synthesized one, evidently validating the framework robustness of ZSF-1. Atomic absorption spectrometer (AAS) analysis of the supernatant revealed negligible metal ion leaching (2.13 ppm for Ni2+ and 2.02 ppm for Zr4+) of ZSF-1 during catalytic reaction, unambiguously confirming the heterogeneous nature of this reaction. These results ascertained that ZSF-1 not only enables the direct use of imitated flue gases for CO2 chemical fixation, but also can be reused for several times without losing its catalytic activity. It is not surprising to witness the superior catalytic performance of ZSF-1 in this reaction considering its high thermal and chemical stability as well as collaborative catalytic sites. Note 11



that the chiral catalyst ZSF-1 did not give detectable ee values under this reaction conditions. Further lowering the temperature to 50 oC or 25 oC did not gain any improvements. We therefore proposed that ZSF-1 might not be appropriate for the enantioselective synthesis of cyclic carbonates from CO2 and epoxides. The syntheses of cyclic carbonates from CO2 with other epoxides were then conducted to test the general applicability of ZSF-1. Epichlorohydrin was found to be highly active, giving almost quantitive conversion to the resulting cyclic carbonate (Table 2, entry 3). The time-course curves implied this reaction could reach 90% yield in 4 h, and accomplished within 5 h, which is far more efficient than other substrates (Figures S14 and S15), and gives a very high turnover frequency (TOF) of 792. This high activity of epichlorohydrin results from the electron-withdrawing Cl group which promotes the nucleophilic attack of Br- during the ring-opening process. 1,2-epoxyhexane and 1,2-epoxydecane with varied chain lengths give the corresponding products with a yield of 91% and 73%, respectively (Table 2, entries 5 and 7). The discrepancy in the yields of these two substrates lies in the confinement effect of ZSF-1, which limits the free transport of bulky substances through the framework windows. For cyclohexane oxide, the steric hindrance imposed by the cyclohexane ring lead to lower yield (Table 2, entry 9). ZSF-2 was also employed in the same catalytic system and showed excellent activity. All the substrates catalyzed by ZSF-2 showed similar yields to ZSF-1 except for 1,2-epoxyhexane (Table 2, entry 6). We proposed this difference might be ascribed to the more narrow openings of ZSF-2, which restricts the diffusion rate of 1,2-epoxyhexane to the cavities. On the other hand, the same substrate can travel freely through the windows of ZSF-1, resulting in higher yield under the same time period. Again, this phenomenon emphasizes the structure-function correlation of MOFs. Although numerous MOFs catalysts have been employed for the synthesis of cyclic carbonates from CO2 and epoxides, exploring highly efficient and stable heterogeneous catalysts for the direct industrial CO2 chemical fixation remains a challenge. Thanks to their high stability, ZSF-1 and ZSF-2 showed outstanding catalytic performances upon the exposure to the mixed gases of SO2, CO2 and H2O at high temperatures. Meanwhile, the catalysts can be reused for several times without losing their activities. The superior features of these ZSFs enable them to be very potential materials for practical CO2 chemical fixation in industry.

12


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Table 1. Optimization of reaction parameters for cycloaddition of CO2 with styrene oxide catalyzed by ZSF-1.a Entry

Catalyst

Additive

Temperature(oC)

Atmosphere

1

-

TBAB

100

CO2

27

2

ZSF-1

-

100

CO2

6

3

ZSF-1

TBAB

25

CO2

11

4

ZSF-1

TBAB

50

CO2

37

5

ZSF-1

TBAB

100

CO2

94

6c

Conversion (%)b

Cy-salen-Ni

TBAB

100

CO2

61

7

d

ZSF-1

TBAB

100

CO2+H2O

93

8

e

ZSF-1

TBAB

100

CO2+ H2O+SO2

91

9

f

ZSF-1

TBAB

100

CO2+ H2O +SO2

92

10g

ZSF-1

TBAB

100

CO2+ H2O +SO2

90

11h

ZSF-1

TBAB

100

CO2+ H2O +SO2

89

i

ZSF-1

TBAB

100

CO2+ H2O +SO2

87

12 a

Reaction conditions: epoxide (4 mmol), ZSF-1 (0.025 mol%, ) and TBAB (0.25 mol%) under CO2 (1 atm), 100 oC,

reaction time 20 h. bConversions were determined by GC-MS. c0.25 mol% Cy-salen-Ni was used. d0.1 mL H2O was added to the reaction. e0.1 mL H2O was added to the reaction; P (CO2) : P (SO2) = 1:1. fsecond cycle. gthird cycle. hfourth cycle. ififth cycle. Table 2. The syntheses of cyclic carbonates catalyzed by ZSF-1 and ZSF-2.a Entry

Epoxide

1

O

2 3e

O

Catalyst

Conversion (%)b

TONc

TOFd

ZSF-1

94

3760

188

ZSF-2

93

3720

186

ZSF-1

99

3960

792

ZSF-2

99

3960

792

ZSF-1

91

3640

182

ZSF-2

72

2880

144

ZSF-1

73

2920

146

ZSF-2

71

2840

142

ZSF-1

18

720

36

ZSF-2

16

640

32

Cl

4e 5

O

6 7

O

8 9 O

10 a

Reaction conditions: epoxide (4 mmol), catalyst (0.025 mol%) and TBAB (0.25 mol%) under CO2 (1 atm), 100 oC,

reaction time 20 h. bConversions were determined by GC-MS. cTON: moles of cyclic carbonate per mole of catalyst used. dTOF: TON/time (h). ereaction time: 5 h. 13



Page 14 of 27

Enantioselective C-H Azidation Reaction Organic azides have been widely used in biological chemistry, pharmaceutical discovery and material

science

because

of

their

versatile

synthetic

functions

to

transform

into

nitrogen-containing groups such as amines, imines, amides, nitrile and triazoles. Additionally, the recent flourishing of click chemistry makes organic azides highly indispensable roles in surface modification, character decoration and preparation of many novel materials.49 These appealing properties have driven vigorous research of the synthetic routes for accessing organic azides. Among these, direct C-H activation offers a facile strategy to introduce azides groups in a single step, avoiding the tedious pre-functionalization process. We have developed a palladium-catalyzed regioselective azidation of allylic C-H bonds with NaN3 as the azide source under O2.50 This method provides a simple and efficient route to allylic azides through direct C-H activation with a wide substrate scope. Despite the significant progress in this field, the enantioselective C-H azidation reaction remains comparatively rare and is highly desirable because of the crucial role of organic azides in natural medicine filed.51 Groves et al. recently developed an elegant late-stage aliphatic C-H azidation catalyzed by predesigned Mn(III) compounds with NaN3 as the azide source.52 In this catalytic system, they reported a single example of a 70% ee for the azidation product of celestolide using chiral Mn(III)-salen Jacobsen catalyst. Herein, we envision that the integration of large porosity, well-established catalytic microenvironment, diverse chiral groups and high chemical stability towards moisture makes ZSFs very promising heterogeneous catalysts for the enantioselective C-H azidation reaction. The ZSF-3 and ZSF-4 with Mn3+ ion as the catalytic site were applied to the enantioselective C-H azidation reaction. Before the reaction, the catalysts were fully activated to remove the residue solvents in the cavities. By utilizing the reaction conditions illustrated in Grove’s work,52 ZSF-4 (1 mol %), phenylpropane (0.6 mmol), iodosobenzene (PhIO, 5 eq.), NaN3 (1.5 M, 1 mL), ethyl acetate (1 mL) were mixed and stirred at room temperature. The catalytic result implied a yield of only 40 % (Table S2, entry 1), which is obviously lower than that reported in Grove’s work (66 %). This reduced yield results from the lower selectivity (43%) towards azidation product than oxygenation side product. We propose the heterogeneous nature of ZSF-4 accounts for the low selectivity in this reaction. The introduction of heterogeneous MOF catalyst makes the 14


Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reaction a triphase catalytic system, which hinders the complete interaction between the active centers and substrate, thus rendering reduced azidation product selectivity. Considering this, we turn our effort to other solvents that are miscible with water. Various solvents such as EtOH, THF, DMF and acetone were screened and acetone was found to be the optimal selection, affording 98% conversion, 66% selectivity and 68% ee (Table S2, entry 5). This improvement is largely related to the free immigration of N3- from aqueous phase to organic phase to sufficiently react with the catalyst. The effects of the amount of oxidant on the conversion, selectivity and ee value were then investigated. Reducing the amount of oxidant to 4 eq. will lead to decreased conversion (82%), but with increased selectivity (76%) and ee values (93%) (Table S2, entry 6). This phenomenon might be attributed to the decreased mass transfer resistance through the reduction of PhIO, facilitating the substrate to be more easily entrapped into the cavities of ZSF-4 and then interact with the chiral groups in close proximity. Further decreasing the amount of PhIO to 3 eq. leads to remarkably decreased yield (Table S2, entry 7). The use of (S)-ZSF-4 gave the reversed enantiomer with 94% ee, which indicated the enantioselectivity of the product was controlled by the intrinsic chiral nature of the catalyst (Table S2, entry 8). The ZSF-3 was also applied in this reaction under identical reaction conditions. The result revealed similar yield but reduced ee value (75%) compared to ZSF-4, which implied that the chiral diphenyl groups offer better stereo control over cyclohexane groups for this reaction (Table 3, entry 1). A further comparison between ZSF-3/ZSF-4 and their corresponding homogeneous molecular metallosalen species with five times of catalysts loading was conducted. Impressively, the MOF catalysts are apparently overwhelmed the molecular catalysts in various aspects. The time-course curves of ZSF-3 and ZSF-4, and homogeneous metallosalen in this reaction provide much more insights into this phenomenon. As can be seen from Figures S16 and S17, the initial conversions of the reaction using molecular catalysts are higher than that using MOF catalyst, which may be attributed to the faster interaction between the substrate and the dissolvable molecular catalysts. However, with the proceeding of the reaction, the catalytic reaction showed obvious decreased selectivity, indicating the gradual deactivation of the molecular catalysts. In contrast, the reactions catalyzed by ZSF-3 and ZSF-4 always maintained their product selectivity, giving apparently enhanced catalytic activity. Apart from that, the enantioselectivity of ZSF-3 and ZSF-4 also outperformed that of the corresponding counterparts. These superior performances of ZSF-3 and ZSF-4 can be explained 15



Page 16 of 27

by their rigid framework and well decorated catalytic microenvironment. As mentioned above, the metallosalen linkers are well separated and anchored at the fixed position within the framework with the unsaturated sites directing to the inner chiral cages. This structural feature not only inhibits the deactivation pathways and makes each metallosalen center highly active, but also generates a confined chiral cage that facilitates the synergistic activation and chirality transfer of substrates. For comparison, the multimolecular deactivation pathways of molecular catalysts are inevitably occurred with the proceeding of the reaction, which results in the catalytically inactive dimmers and then the obviously decreased product selectivity. Indeed, in Grove’s work,52 extra fresh homogeneous catalyst has to be added to the reaction system at intervals to compromise the multimolecular deactivation. Here the MOF catalysts could effectively overcome this drawback and simplify the working procedure. It is noteworthy that the viscous solution of this reaction makes the recycle of the catalyst very difficult, which results in the gradual decrease of the conversion in the second and third cycle (Figure S18). Notwithstanding, the PXRD patterns of the recycled catalyst remained unaltered as the fresh one, indicating the maintenance of the cystallinity after the reaction (Figure S18). Meanwhile, AAS analysis of the supernatant suggested no obvious metal ion leaching in this reaction, which confirmed the heterogeneous nature of this reaction. The above results implied that the ZSFs give high catalytic activity and enantioselectivity in this water-mediated C-H azidation reaction without disturbing their framework integrity. This superior catalytic performance could be ascribed to the well defined active sites and enhanced water resistance of ZSF-3 and ZSF-4, which are usually absence in many MOFs, but are of vital importance for practical application of MOFs. The

reaction

was

then

extended

to

other

substrates

such

as

4-propyltoluene,

1-bromo-4-propylbenzene, 1,2-dihydrostilbene and celestolide. The results suggested that phenylpropane bearing either electron-withdrawing or electron-donor groups both gave good yields and excellent enantioselectivities (Table 3, entries 5-12). Impressively, 1,2-dihydrostilbene was also found to be highly effective in this reaction and give high yields and moderate to good enantioselectivities (Table 3, entries 13-16). In this case, the ZSF-3 bearing chiral cyclohexane group affords conspicuously enhanced stereo control over ZSF-4 with chiral diphenyl groups. For comparison, the difference in the enantioselectivity of 1,2-dihydrostilbene catalyzed by molecular catalyst is far less obvious than ZSF-3 and ZSF-4. This phenomenon implied that the 16


Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


enantioselectivity of the reaction was controlled by both the chiral groups and the confined porous structures of these chiral MOFs. We then seek to apply these catalysts to more complex bioactive molecule celestolide to evaluate their usages to late-stage functionalization (Table 3, entries 17-20). With only 2 eq. PhIO, the reaction could accomplish for both MOFs and molecular catalysts with similar yields and enantioselectivities. The reason for this catalytic result could be attributed to two aspects. Firstly, the high activity of celestolide makes the reaction proceed in shorter time period, during which the molecular catalysts are still active, thus giving similar yields to heterogeneous MOF catalysts. Secondly, the windows of ZSF-3 and ZSF-4 are supposed to inhibit the free passing of the bulky and rigid celestolide molecule, which makes the reaction of celestolide mainly on the surface of MOFs, thereby resulting in comparable enantioselectivities with molecular catalysts. These results highlight the significant role of MOF structures in determining the catalytic performances of specific reactions. Table 3. The syntheses of organic azides catalyzed by ZSF-3, ZSF-4 and corresponding molecular catalysts.a Entry

Catalyst

1

ZSF-3

2

ZSF-4

3

Substrate

Product

Conversion (%)

Selectivity (%)

ee (%)

82

72

75

82

76

93

Cy-salen-Mn

63

43

62

4

Ph-salen-Mn

65

45

80

5

ZSF-3

86

70

77

6

ZSF-4

80

68

82

7

Cy-salen-Mn

53

48

51

8

Ph-salen-Mn

48

45

53

9

ZSF-3

78

65

60

10

ZSF-4

81

67

70

11

Cy-salen-Mn

45

46

20

12

Ph-salen-Mn

50

35

36

13

ZSF-3

80

71

70

N3

N3

N3

Br Br

N3

14

ZSF-4

79

64

45

15

Cy-salen-Mn

56

62

21

17



Page 18 of 27

16

Ph-salen-Mn

47

57

14

17

ZSF-3

99

61

30

18

ZSF-4

99

64

15

19

Cy-salen-Mn

88

59

30

86

58

12

N3 O

20 a

O

Ph-salen-Mn

Reaction conditions: substrate (0.6 mmol), ZSF-3 or ZSF-4 (0.5 mol%), Cy-salen-Mn or Ph-salen-Mn (5 mol%),

NaN3 (1.5 M, 1 mL) and PhIO (2-4 eq. added in portions with 1 eq. each time), acetone (1 mL), rt.

Postsynthetic Demetallation and Remetallation The aforementioned results implied that the robust ZSF-1~4 with different metal centers gave excellent catalytic behaviors in specific reactions. Further engineering metallosalen-based Zr-MOFs catalytic platform with other metal active sites is thus of particular interest for their broader applications. The postsynthetic removal of the Mn ions from the salen struts of corresponding MOFs using aqueous H2O2 have been proved to be an effective strategy to tune the active sites and then the properties.12 Using this strategy, we demetallated the Mn3+ ion in ZSF-4 and then remetallated it with Cu2+, Fe3+ and Ti4+ ions. This process involved the dramatic changes in the colors of the samples with PXRD patterns unaltered (Figure S20). Besides, XPS analyses indicated the remetallation of Cu2+, Fe3+ and Ti4+ ions in the corresponding MOFs (Figure S21). Although it is well documented that the reactive hydroxyl groups on the Zr nodes can be used to deposit metal ions[53], the coordination between salen and metal ions is stronger than that of µ-OH groups from Zr6O4(OH)4 clusters because salen is a tetradentate chelating ligand and has higher crystal filed stabilization energy. Therefore, this modification here brings about new analogues of robust metallosalen-based Zr-MOFs and may thus give much more abundant properties.

Conclusions The chemical stability of MOFs catalysts is of vital importance for the practical applications as the frameworks intactness allows their catalytic performance to be fully exerted and their reuse. In this work, we report, for the first time, the construction of a novel class of chiral metallosalen-based

Zr-MOFs

through

modulated

synthetic

approach

and/or

demetallization-remetallization strategy. The higher linker-node connectivity of Zr6O4(OH)4 clusters with strong Zr-O bond and the hydrophobic groups on metallosalen ligand impart ZSFs 18


Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the high chemical stability over a wide of range of pH values in aqueous and organic solutions. The ease of introduction of different chiral groups and various catalytic metal centers into metallosalen linker and the porosity of UiO-type MOFs endow these robust ZMFs outstanding catalytic platform for abundant organic transformations. As recyclable heterogeneous catalysts, ZSF-1 and ZSF-2 exhibited excellent catalytic efficiency for the cycloaddition of CO2 and epoxides, while ZSF-3 and ZSF-4 demonstrated efficient asymmetric catalytic performance (ee value up to 94%) for C-H azidation reaction in water-involving medium. Moreover, these MOFs activities significantly outperformed the corresponding homogeneous molecular catalysts due to the collaborative activation and/or framework confined chiral cages. The present work not only broadens the application span of chiral metallosalen-based MOFs, especially in aqueous media, but also paves a new way for engineering robust chiral MOFs catalytic platform through rational design strategy. The exploration for more enriched asymmetric catalyses of ZSFs with other active sites is ongoing in our laboratory.

EXPERIMENTAL SECTION A detailed physicochemical characterization and experimental procedures for the metallosalen ligands are provided in the Supporting Information. Only experimental procedures for the MOFs synthesis, crystal structure determination and catalytic procedures are shown below. Syntheses of ZSFs ZSF-1 was synthesized through solvothermal reaction of ZrCl4 (0.02 mmol), Cy-salen-Ni (0.02 mmol) and TFA (0.2 mL) in a solvent of DMF (4 mL) at 120 oC for three days. Then the reaction was cooled to room temperature at a rate of 5 oC/h. The product was isolated by decanting the mother liquor and washing with DMF. ZSF-2~4 were obtained by using metallosalen ligands Ph-salen-Ni, Cy-salen-Mn and Ph-salen-Mn under the similar conditions, respectively. Sample activation Before the adsorption tests, the as-synthesized samples of ZSF-1~4 were washed with DMF for three times and then immersed in THF solution for 3 days for solvent exchange. During the exchange process, THF was refreshed every 24 h. After that, the exchanged samples of ZSF-1~4 were activated at 100 oC under high vacuum for 24 h, giving activated samples of ZSF-1~4 with

19



the formulas of [C180H208N12O44Ni6Zr6], [C228H220N12O44Ni6Zr6], [C180H208N12O44Cl6Mn6Zr6] and [C228H220N12O44Cl6Mn6Zr6], respectively. X-ray Crystallography Single crystal XRD analysis of ZSF-1 was performed on an Xcalibur Onyx Nova four-circle diffractometer using CuKα radiation (λ = 1.54184 Å) at 100 K. The empirical absorption correction was performed using the CrystalClear program. The structure was solved by direct methods and refined on F2 by full-matrix least-squares technique using the SHELX-2014 program package.54 The metal atoms in the asymmetric unit were located firstly from the difference Fourier map and refined anisotropically. The other atoms (O, C and N) in ligand were then located from the difference Fourier map and refined isotropically, as a result of the relatively weak diffraction. Restraints DFIX for bond lengths of salen framework were applied. SQUEEZE subroutine of the PLATON software suite55 was applied to remove the scattering from the highly disordered guest molecules. The resulting new HKL file was used to further refine the structure. Hydrogen atoms attached to carbon were placed in geometrically idealized positions and refined using a riding model. Crystallographic data are summarized in Table S1. CCDC 1852696 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre. Cycloaddition of CO2 with Epoxides Epoxides (4 mmol), ZSF-1 (0.025 mol%, 4 mg) or ZSF-2 (0.025 mol%, 4.7 mg), and n-tetrabutylammonium bromide (TBAB) (0.25 mol%, 3.2 mg) were mixed in a schlenk flask with a magnet bar. The mixture was outgassed completely and then purged with CO2. This operation was repeated for three times before the mixture was stirred at 100 oC for 20 h with a CO2 balloon. Upon completion, the mixture was filtered to remove the solid phrase and the filtrate was analyzed with GC-MS to give the conversion. Enantioselective C-H Azidation Reaction. Substrates (0.6 mmol), ZSF-3 (1 mol%, 26 mg) or ZSF-4 (1 mol%, 29.5 mg), iodosylbenzene (132 mg, 1 equiv.) and 1 mL acetone were mixed in a 10 mL dried vial, followed by the addition of 1 mL 1.5 M sodium azide aqueous solution. The vial was capped and stirred at room temperature. Another portion of 1.5 M sodium azide solution (0.1 mL) and iodosylbenzene (132 mg) were added to the mixture and stirred at room temperature after the consumption of the solid 20


Page 20 of 27

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iodosylbenzene. The reaction progress was monitored by GC-MS and LC. After the completion of the reaction, the mixture were extracted with 10 mL brine and 10 mL of ethylacetate for three times. The combined organic layer was dried with anhydrous sodium sulfate and then evaporated to remove the solvent. The product was isolated from the reaction crude by flash chromatography. The ee values of the product were then determined by HPLC CHIRALCEL IA, IB or IC chiral columns.

ASSOCIATED CONTENT Supporting Information Detailed procedures for PXRD, TGA, NMR, UV-vis and the synthesis of the metallosalen ligands; crystallographic data of ZSF-1; additional structural figure; SEM images; Ar and CO2 gas adsorption isotherms; CD spectra; XPS spectra; and HPLC spectra, including Tables S1 and S2, and Figures S1-S20. X-ray crystallographic data in CIF format for ZSF-1.

AUTHOR INFORMATION Corresponding Authors *Fax: +86-20-87112906. E-mail: [email protected] (Y. W. Ren). *Fax: +86-20-87112906. E-mail: [email protected] (H. F. Jiang).

ACKNOWLEDGMENTS This work was supported by the National Key Research and Development Program of China (2016YFA0602900) and the National Natural Science Foundation of China (21372087).

REFERENCES 1.

Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. Enantioselective Epoxidation of

Unfunctionalized Olefins Catalyzed by (Salen)Manganese Complexes. J. Am. Chem. Soc. 1990, 112, 2801-2803. 2.

Schaus, S. E.; Brandes, B. D.; Larrow, J. F.; Tokunaga, M.; Hansen, K. B.; Gould, A. E.;

Furrow, M. E.; Jacobsen, E. N. Highly Selective Hydrolytic Kinetic Resolution of Terminal Epoxides Catalyzed by Chiral (salen)Co-III Complexes. Practical Synthesis of Enantioenriched Terminal Epoxides and 1,2-Diols. J. Am. Chem. Soc. 2002, 124, 1307-1315. 21



3.

Nishikori, H.; Katsuki, T. Catalytic and Highly Enantioselective Aziridination of Styrene

Derivatives. Tetrahedron Lett. 1996, 37, 9245-9248. 4.

Katsuki, T. Chiral Metallosalen Complexes: Structures and Catalyst Tuning for Asymmetric

Epoxidation and Cyclopropanation. Adv. Synth. Catal. 2002, 344, 131-147. 5.

Zeng, X.-P.; Cao, Z.-Y.; Wang, X.; Chen, L.; Zhou, F.; Zhu, F.; Wang, C.-H.; Zhou, J.

Activation of Chiral (Salen)AlCl Complex by Phosphorane for Highly Enantioselective Cyanosilylation of Ketones and Enones. J. Am. Chem. Soc. 2015, 138, 416-425. 6.

Bartoli, G.; Bosco, M.; Carlone, A.; Locatelli, M.; Massaccesi, M.; Melchiorre, P.; Sambri, L.

Asymmetric Aminolysis of Aromatic Epoxides: A Facile Catalytic Enantioselective Synthesis of Anti-Beta-Amino Alcohols. Org. Lett. 2004, 6, 2173-2176. 7.

Bhunia, A.; Dey, S.; Moreno, J. M.; Diaz, U.; Concepcion, P.; Van Hecke, K.; Janiak, C.; Van

Der Voort, P. A Homochiral Vanadium-Salen Based Cadmium bpdc MOF with Permanent Porosity as An Asymmetric Catalyst in Solvent-Free Cyanosilylation. Chem. Commun. 2016, 52, 1401-1404. 8.

Chen, D.; Luo, R.; Li, M.; Wen, M.; Li, Y.; Chen, C.; Zhang, N. Salen(Co(III)) Imprisoned

within Pores of A Metal-Organic Framework by Post-Synthetic Modification and Its Asymmetric Catalysis for CO2 Fixation at Room Temperature. Chem. Commun. 2017, 53, 10930-10933. 9.

Li, J.; Fan, Y.; Ren, Y.; Liao, J.; Qi, C.; Jiang, H. Development of Isostructural

Porphyrin-Salen Chiral Metal-Organic Frameworks Through Postsynthetic Metalation Based on Single-Crystal to Single-Crystal Transformation. Inorg. Chem. 2018, 57, 1203-1212. 10. Li, J.; Ren, Y.; Qi, C.; Jiang, H. The First Porphyrin-Salen Based Chiral Metal-Organic Framework for Asymmetric Cyanosilylation of Aldehydes. Chem. Commun. 2017, 53, 8223-8226. 11. Li, J.; Ren, Y.; Qi, C.; Jiang, H. A Chiral Salen-Based MOF Catalytic Material with High Thermal, Aqueous and Chemical Stabilities. Dalton Trans. 2017, 46, 7821-7832. 12. Shultz, A. M.; Sarjeant, A. A.; Farha, O. K.; Hupp, J. T.; Nguyen, S. T. Post-Synthesis Modification of A Metal-Organic Framework to Form Metallosalen-Containing MOF Materials. J. Am. Chem. Soc. 2011, 133, 13252-13255. 13. Song, F. J.; Wang, C.; Falkowski, J. M.; Ma, L. Q.; Lin, W. B. Isoreticular Chiral Metal-Organic Frameworks for Asymmetric Alkene Epoxidation: Tuning Catalytic Activity by Controlling Framework Catenation and Varying Open Channel Sizes. J. Am. Chem. Soc. 2010, 132, 22


Page 22 of 27

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15390-15398. 14. Zhu, C.; Yuan, G.; Chen, X.; Yang, Z.; Cui, Y. Chiral Nanoporous Metal-Metallosalen Frameworks for Hydrolytic Kinetic Resolution of Epoxides. J. Am. Chem. Soc. 2012, 134, 8058-8061. 15. Xia, Q. C.; Li, Z. J.; Tan, C. X.; Liu, Y.; Gong, W.; Cui. Y. Multivariate Metal-Organic Frameworks as Multifunctional Heterogeneous Asymmetric Catalysts for Sequential Reactions. J. Am. Chem. Soc. 2017, 139, 8259-8266. 16. Yuan, G. Z.; Jiang, H.; Zhang, L. Y.; Liu, Y.; Cui, Y. Metallosalen-Based Crystalline Porous Materials: Synthesis and Property. Coord. Chem. Rev. 2017, DOI: 10.1016/j.ccr.2017.10.032. 17. Han, X.; Xia, Q.; Huang, J.; Liu, Y.; Tan, C.; Cui, Y. Chiral Covalent Organic Frameworks with High Chemical Stability for Heterogeneous Asymmetric Catalysis. J. Am. Chem. Soc. 2017, 139, 8693-8697. 18. Li, L.-H.; Feng, X.-L.; Cui, X.-H.; Ma, Y.-X.; Ding, S.-Y.; Wang, W. Salen-Based Covalent Organic Framework. J. Am. Chem. Soc. 2017, 139, 6042-6045. 19. Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surble, S.; Margiolaki, I. A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area. Science 2005, 309, 2040-2042. 20. Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A New Zirconium Inorganic Building Brick Forming Metal Organic Frameworks with Exceptional Stability. J. Am. Chem. Soc. 2008, 130, 13850-13851. 21. Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R. D.; Uribe-Romo, F. J.; Chae, H. K.; O'Keeffe, M.; Yaghi, O. M. Exceptional Chemical and Thermal Stability of Zeolitic Imidazolate Frameworks. P. Natl. Acad. Sci. 2006, 103, 10186-10191. 22. Fateeva, A.; Chater, P. A.; Ireland, C. P.; Tahir, A. A.; Khimyak, Y. Z.; Wiper, P. V.; Darwent, J. R.; Rosseinsky, M. J. A Water-Stable Porphyrin-Based Metal-Organic Framework Active For Visible-Light Photocatalysis. Angew. Chem. Int. Ed. 2012, 51, 7440-7444. 23. Feng, D.; Chung, W.-C.; Wei, Z.; Gu, Z.-Y.; Jiang, H.-L.; Chen, Y.-P.; Darensbourg, D. J.; Zhou, H.-C. Construction of Ultrastable Porphyrin Zr Metal-Organic Frameworks Through Linker Elimination. J. Am. Chem. Soc. 2013, 135, 17105-17110. 24. Feng, D.; Gu, Z.-Y.; Chen, Y.-P.; Park, J.; Wei, Z.; Sun, Y.; Bosch, M.; Yuan, S.; Zhou, H.-C. 23



Page 24 of 27

A Highly Stable Porphyrinic Zirconium Metal-Organic Framework with shp-a Topology. J. Am. Chem. Soc. 2014, 136, 17714-17717. 25. Feng, D.; Gu, Z.-Y.; Li, J.-R.; Jiang, H.-L.; Wei, Z.; Zhou, H.-C. Zirconium-Metalloporphyrin PCN-222: Mesoporous Metal-Organic Frameworks with Ultrahigh Stability as Biomimetic Catalysts. Angew. Chem. Int. Ed. 2012, 51, 10307-10310. 26. Jiang, H.-L.; Feng, D.; Wang, K.; Gu, Z.-Y.; Wei, Z.; Chen, Y.-P.; Zhou, H.-C. An Exceptionally Stable, Porphyrinic Zr Metal-Organic Framework Exhibiting pH-Dependent Fluorescence. J. Am. Chem. Soc. 2013, 135, 13934-13938. 27. Wang, K.; Feng, D.; Liu, T.-F.; Su, J.; Yuan, S.; Chen, Y.-P.; Bosch, M.; Zou, X.; Zhou, H.-C. A Series of Highly Stable Mesoporous Metalloporphyrin Fe-MOFs. J. Am. Chem. Soc. 2014, 136, 13983-13986. 28. Zhang, Y.; Guo, J,; Shi, L,; Zhu, Y.-F.; Hou, K.; Zheng, Y.-L.; Tang, Z.-Y. Tunable Chiral Metal Organic Frameworks Toward Visible Light-Driven Asymmetric Catalysis. Sci. Adv. 2017, 3:e1701162. 29. Wang, K.; Lv, X.-L.; Feng, D.; Li, J.; Chen, S.; Sun, J.; Song, L.; Xie, Y.; Li, J.-R.; Zhou, H.-C.

Pyrazolate-Based

Porphyrinic

Metal-organic

Framework

with

Extraordinary

Base-Resistance. J. Am. Chem. Soc. 2016, 138, 914-919. 30. Wang, S.; Wang, J.; Cheng, W.; Yang, X.; Zhang, Z.; Xu, Y.; Liu, H.; Wu, Y.; Fang, M. A Zr Metal-Organic Framework Based on Tetrakis(4-carboxyphenyl) Silane and Factors Affecting the Hydrothermal Stability of Zr-MOFs. Dalton Trans. 2015, 44, 8049-8061. 31. Diring, S. p.; Furukawa, S.; Takashima, Y.; Tsuruoka, T.; Kitagawa, S. Controlled Multiscale Synthesis of Porous Coordination Polymer in Nano/Micro Regimes. Chem. Mater. 2010, 22, 4531-4538. 32. Tsuruoka, T.; Furukawa, S.; Takashima, Y.; Yoshida, K.; Isoda, S.; Kitagawa, S. Nanoporous Nanorods Fabricated by Coordination Modulation and Oriented Attachment Growth. Angew. Chem. Int. Ed. 2009, 48, 4739-4743.. 33. Schaate, A.; Roy, P.; Godt, A.; Lippke, J.; Waltz, F.; Wiebcke, M.; Behrens, P. Modulated Synthesis of Zr-Based Metal-Organic Frameworks: from Nano to Single Crystals. Chem. Eur. J. 2011, 17, 6643-6651. 34. Islamoglu, T.; Otake, K. I.; Li, P.; Buru, C. T.; Peters, A. W.; Akpinar, L.; Garibay, S. J.; Farha, 24


Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


O. K. Revisiting the Structural Homogeneity of NU-1000, a Zr-Based Metal-Organic Framework. CrystEngComm, 2018, DOI: 10.1039/C8CE00455B. 35. Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving Surface Chemical States in XPS Analysis of First Row Transition Metals, Oxides and Hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717-2730. 36. Han, Q.; Qi, B.; Ren, W.; He, C.; Niu, J.; Duan, C. Polyoxometalate-Based Homochiral Metal-Organic Frameworks for Tandem Asymmetric Transformation of Cyclic Carbonates from Olefins. Nat. Commun. 2015, 6, 10007. 37. He, T.; Ni, B.; Xu, X.; Li, H.; Lin, H.; Yuan, W.; Luo, J.; Hu, W.; Wang, X. Competitive Coordination Strategy to Finely Tune Pore Environment of Zirconium-Based Metal-Organic Frameworks. ACS Appl. Mater. Inter. 2017, 9, 22732-22738. 38. Li, J.; Ren, Y.; Qi, C.; Jiang, H. Fullymeta-Substituted 4,4′-Biphenyldicarboxylate-Based Metal-Organic Frameworks: Synthesis, Structures, and Catalytic activities. Eur. J. Inorg. Chem. 2017, 2017, 1478-1487. 39. Li, P.-Z.; Wang, X.-J.; Liu, J.; Lim, J. S.; Zou, R.; Zhao, Y. Triazole-Containing Metal-Organic Framework as A Highly Effective and Substrate Size-Dependent Catalyst for CO2 Conversion. J. Am. Chem. Soc. 2016, 138, 2142-2145. 40. Liang, J.; Huang, Y.-B.; Cao, R. Metal-Organic Frameworks and Porous Organic Polymers for Sustainable Fixation of Carbon Dioxide into Cyclic Carbonates. Coord. Chem. Rev. 2017, DOI: 10.1016/j.ccr.2017.11.013. 41. Zhang, G.; Wei, G.; Liu, Z.; Oliver, S. R. J.; Fei, H. A Robust Sulfonate-Based Metal-Organic Framework with Permanent Porosity for Efficient CO2 Capture and Conversion. Chem. Mater. 2016, 28, 6276-6281. 42. Zhang, G.; Yang, H.; Fei, H. Unusual Missing Linkers in An Organosulfonate-Based Primitive-Cubic (pcu)-Type Metal-Organic Framework for CO2 Capture and Conversion Under Ambient Conditions. ACS Catal. 2018, 8, 2519-2525. 43. Zhao, D.; Liu, X.-H.; Guo, J.-H.; Xu, H.-J.; Zhao, Y.; Lu, Y.; Sun, W.-Y. Porous Metal-Organic Frameworks with Chelating Multiamine Sites for Selective Adsorption and Chemical Conversion of Carbon Dioxide. Inorg. Chem. 2018, 57, 2695-2704. 44. Ren, Y.; Cheng, X.; Yang, S.; Qi, C.; Jiang, H.; Mao, Q. A Chiral Mixed Metal–Organic 25



Framework Based On A Ni(saldpen) Metalloligand: Synthesis, Characterization and Catalytic Performances. Dalton Trans. 2013, 42, 9930. 45. Ren, Y. W.; Shi, Y. C.; Chen, J. X.; Yang, S. R.; Qi, C. R.; Jiang, H. F. Ni(salphen)-Based Metal-Organic Framework for The Synthesis of Cyclic Carbonates by Cycloaddition of CO2 to Epoxides. RSC Adv. 2013, 3, 2167-2170. 46. Ugale, B.; Dhankhar, S. S.; Nagaraja, C. M. Construction of 3-Fold-Interpenetrated Three-Dimensional Metal-Organic Frameworks of Nickel(II) for Highly Efficient Capture and Conversion of Carbon Dioxide. Inorg. Chem. 2016, 55, 9757-9766. 47. Fan, Y. M.; Li, J. W.; Ren, Y. W.; Jiang, H. F. A Ni(salen)-Based Metal-Organic Framework: Synthesis, Structure, and Catalytic Performance for CO2 Cycloaddition with Epoxides. Eur. J. Inorg. Chem. 2017, 4982-4989. 48. Xu, X. C.; Song, C. S.; Wincek, R. T.; Andresen, J. A.; Miller, B. G.; Scaroni, A. W. Separation of CO2 From Power Plant Flue Gas Using A Novel CO2 "Molecular Basket" Adsorbent. Abstr. Pap. Am. Chem. S. 2003, 225, U854-U855. 49. Brase,S.;Banert,K. Organic Azides: Synthesis and Applications;Wiley-VCH: Weinheim, 2010 50. Chen, H.; Yang, W.; Wu, W.; Jiang, H. Palladium-Catalyzed Regioselective Azidation of Allylic C-H Bonds Under Atmospheric Pressure of Dioxygen. Org. Biomol. Chem. 2014, 12, 3340-3343. 51. Deng, Q.-H.; Bleith, T.; Wadepohl, H.; Gade, L. H. Enantioselective Iron-Catalyzed Azidation of β-Keto Esters and Oxindoles. J. Am. Chem. Soc. 2013, 135, 5356-5359. 52. Huang, X.; Bergsten, T. M.; Groves, J. T. Manganese-Catalyzed Late-Stage Aliphatic C-H Azidation. J. Am. Chem. Soc. 2015, 137, 5300-5303. 53. Manna, K.; Ji, P.-F.; Lin, Z.-K.; Greene, F. X.; Urban, A.; Thacker, N. C.; Lin, W.-B. Chemoselective Single-Site Earth-Abundant Metal Catalysts at Metal-Organic Framework Node. Nat. Commun. 2016, 7, 12610. 54. Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2015, 71, 3-8. 55. Spek, A. L. Single-Crystal Structure Validation With The Program PLATON. J Appl Crystallogr 2003, 36, 7-13.

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Highly Stable Chiral ZirconiumâMetallosalen Frameworks for CO2

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