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Synthesis, structure and properties of new Mg(II)-metal-organic framework and its prowess as catalyst in the production of 4H-pyrans Kranthi Kumar Gangu, Suresh Maddila, Saratchandra Babu Mukkamala, and Sreekantha Babu Jonnalagadda Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04795 • Publication Date (Web): 03 Mar 2017 Downloaded from http://pubs.acs.org on March 8, 2017

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Industrial & Engineering Chemistry Research

Synthesis, structure and properties of new Mg(II)-metal-organic framework and its prowess as catalyst in the production of 4H-pyrans Kranthi Kumar Gangu a, Suresh Maddila a, Saratchandra Babu Mukkamala b, Sreekantha B Jonnalagadda a,* a,

* School of Chemistry & Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban 4000, South Africa

b

Department of Chemistry, GITAM Institute of Science, GITAM University, Visakhapatnam – 530045, Andhra Pradesh, India.

*Corresponding Author: Sreekantha B. Jonnalagadda School of Chemistry & Physics, University of KwaZulu-Natal, Durban 4000, South Africa Tel.: +27 31 2607325, Fax: +27 31 2603091 E-mail address: [email protected]

Abstract: A new alkaline metal-organic framework, [Mg3(NDC)3(DMF)4].H2O (1) is synthesized solvothermally by using 2,6-naphthalenedicarboxylic acid (NDC) as ligand and dimethylformamide (DMF) and water as mixed solvent. Single crystal X-ray studies shows that 1 crystallizes in the space group C2/c with parameters a = 13.4191(2), b = 18.0669(2), c = 20.9746(3) Å, β = 99.66(0)o. The central metal atom Mg(II) adopts a six coordinated octahedral geometry with carboxylate oxygen atoms and DMF molecules. Due to the involvement of oxygen atoms in bridging and chelation binding, a trinuclear secondary building unit is built up, which further connects to other six NDC ligands and finally leading to a three dimensional network. The thermal and luminescent analysis revealed that the compound is thermally stable with violet emission. The creation of coordinatively unsaturated Mg(II) centers, acting as Lewis-acidic sites upon activation, are explored to use 1

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as heterogeneous catalyst in value-added organic conversions. MOF showed a superb catalytic performance in the synthesis of eight 4H-pyran derivatives via one-pot threecomponent reaction between aromatic aldehydes, malononitrile, and cyanoacetamide at room temperature. All the reactions worked exceptionally well with excellent yields (91-96%), in short reaction times (< 40 min). Green solvent (ethanol) and easy separation, reusability and robust

structure

of

catalyst

are

the

attractions

of

the

protocol

and

making

[Mg3(NDC)3(DMF)4].H2O an ideal catalyst for wide-ranging organic transformations.

Keywords: Metal-organic frameworks; Solvothermal; heterogeneous catalysts; Unsaturated metal centers; One-pot MCRs; 4H-pyrans.

1. INTRODUCTION Metal-organic frameworks (MOFs) possessing crystalline and porous nature have emerged as important organic-inorganic hybrid materials in the fields of advanced materials and synthetic chemistry.1-4 The MOFs built from metal node or clusters and organic linkers and their different bonding connections allow for the vibrant structural architectures from onedimensional to three-dimensional.5-8 The striking features such as tunable pore dimensions, permanent porosities, high surface areas and topology of MOFs attract the researchers towards their potential applications in the disciplines of gas storage, catalysis, photonics, drug delivery and magnetism.9-12 The geometry, size and functionality of MOFs basically rely on the selection of constituents as well as their preparation conditions. The aromatic carboxylates in general and naphthalenedicarboxylates in particular are superb building blocks of MOFs and their bonds with metal nodes depend on the availability of deprotonated carboxylic acid groups attached to them.13,14 The richness in coordination modes, remarkable stability, structural rigidity, easily adjustable length and good connectivity nature instill the


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researchers as choice of interest.15-17 Although many studies have been done on transition metals, the coordination chemistry of alkaline earth metals still remains less known. Not many studies describing the coordination polymers of magnesium are available.18 Carboxylates of Mg form coordination polymers due to high affinity of Mg2+ towards donor oxygen atom of polar solvents. Moreover, octahedral geometry is common in magnesium complexes. Coordination chemistry of magnesium is less flexible compared to other metals.19 Although, broad variety of MOFs are reported every year with boundless combinations and compositions of metals and linker precursors, the target application absolutely dictates the design of MOF. The one of the remarkable advantage of MOFs is their scope as heterogeneous catalyst materials.20-22 To tide over the problems associated with homogeneous catalysts, the development of new heterogeneous catalysts is an emergent platform. The deliberate or incidental formation of active sites such as coordinatively unsaturated metal sites (CUMs), functional organic sites (FOS), metal nanoparticles (MNPs) incorporated in the pores as well as metalloligands prompt the MOFs as relevant solid heterogeneous catalysts.23,24 The active sites on the pore surface of MOFs particularly possess charge, chirality, redox potential, polarity, etc. endow the micro catalytic environment to the MOFs, which facilitate the transport of reactants to products.25,26 The wide scope of MOFs preparation using variety of chemical entities, more thermal stabilities (400-500 oC) and the persistence of porosity after de-solvation make superior than the coveted zeolites.27 A variety of organic transformations such as aldol condensation, Knoevenagel condensation, oxidation reactions, Biginelli reaction, Friedel–Crafts reactions, and polymerization have been reported earlier by employing appropriate MOFs as catalysts, which proved MOFs to be as most sought after materials in catalysis.28-30 The removal of coordinated or guest molecules from metal ions up on activation creates Lewis acidic character, which is enormously useful in application as



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catalysts for the multi-component reactions leading to novel organic transformations.31,32 Multi-component reactions (MCRs) are elite synthetic approach, where organic products are synthesized in one step. The use of heterogeneous catalysts in MCRs has increased due to the scope for rapid assembly of molecules and straightforward organic reactions with utmost atom efficiency. 33- 35 The organic molecules with 4H-pyran scaffolds have attracted sizeable attention because of their biological activities as anticancer, anti-HIV, cytotoxic, antimalarial, anti-inflammatory, antimicrobial, antihyperglycemic, and antidyslipidemic etc. Furthermore, the 4H-pyran entities are also used as photoactive materials, as well as intermediates compounds in synthesis of dihydrofurans.36-38 Consequently, the synthesis of various substituted pyran derivatives has been a point of interest and various protocols have been reported using a variety of catalysts, including H6P2W12O62.H2O

39

, PPA-SiO240, Bmim[BF4] 41, L-proline

42

,

hexadecyltrimethyl ammonium bromide (HDTMAB)43 and tetrabutylammonium fluoride (TBAF)44, to mention a few. Many of such reported studies have some limitations accrued in terms of low yields, reaction temperatures, long work up and reaction times. In earlier communications, we reported a series of articles addressing the synthesis of varied heterocyclic moieties by employing different novel catalysts, viz. Cu/ZrO2, metal-doped fluorapatites, nanocomposites, Sm/ZrO2, Mn/ZrO2 and Ce–V/SiO2 with excellent yields and shorter reaction times.45-47 We have also reported the synthesis of number of MOFs by using variety of metal and organic linker precursors. In continuation of our endeavor to explore congenial green protocols for facile synthesis of heterocyclic compounds, herein we report a novel Mg(II) based MOF, its characterization and viability as catalyst in the preparation of 4H-pyran derivatives under environmentally benign reaction conditions.


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2. EXPERIMENTAL 2.1. Materials and instrumentation Reagent grade chemicals and solvents were used as supplied with no further purification. Magnesium chloride hexahydrate, MgCl2.6H2O (Acros Organics); N,N' dimethylformamide, Ethanol (Merck, Germany); 2,6-naphthalenedicarboxylic acid, malononitrile, cyanoacetamide and aromatic aldehydes were procured from Sigma Aldrich. De-ionised water only was employed in all experiments. To obtain IR spectrum, Perkin Elmer “Spectrum Two” FTIR spectrophotometer was used. “Mettler Toledo TGA/DSC-1” apparatus under N2 in the temperature range 25-800oC, with a heating rate of 10oC min-1 was used for thermogravimetric analysis. Thermo Scientific FLASH-2000 elemental analyzer was employed for the C, H, and N microanalyses. Perkin Elmer LS-55 Fluorescence Spectrometer at room temperature was used to record the luminescence spectra of the ligand and MOF. Bruker advance 400 spectrometer at ambient temperature conditions was employed to obtain the 1H, 13C and 15N NMR spectra of the pyran derivatives.

2.2. Preparation of [Mg3(2,6-NDC)3(DMF)4].H2O A typical synthesis involves a mixture of MgCl2.6H2O (0.2 mmol, 0.0406 g) and 2,6naphthalenedicarboxylic acid (0.4 mmol, 0.0864g) dissolved in 10.0 mL of dimethylforamide and 2.0 mL of water and stirred few minutes to get homogeneous solution. The resultant solution was then placed in Teflon lined 23 mL stainless steel autoclave and was heated at 120oC over three days and then cooled to room temperature at a rate of 6oC. A white color crystalline material was collected by filtration and DMF/water mixture was used for further washings. Elemental analysis found: C 56.23%, H 4.47% and N 5.38%. Calculated for C48 H46 Mg3 N4 O17: C 56.31%, H 4.52% and N 5.47%



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2.3. Single crystal X-ray structure determination A CCD Agilent Technologies (Oxford Diffraction) SUPER NOVA diffractometer was employed to generate the single-crystal X-ray diffraction data for both the MOFs. Graphitemonochromoated Mo Kα radiation (λ = 0.71073 Å) at 150(2) K was used for collection of data. The crystal data was analyzed using the CrysAlisPro CCD software and standard phiomega scan techniques for scaling and reducing were done by CrysAlisPro RED software. While SHELXS-9748 by direct methods was used for solving the structures, SHELXL-97 software with full matrix least-squares49 was employed for further refining the structures. All the hydrogen atom locations were identified based on differences in electron density map and were forced to ride on the respective non-hydrogens. Anisotropically, all non-hydrogen atoms were refined. The X-ray diffraction principally relies on the electron density of entities. The atoms possessing more electrons generally have stronger effect of X-rays, while the lighter atoms like hydrogen have difficulty for their localization.50 Hence, in this crystal structure we have included the two undetected hydrogen atoms to uncoordinated oxygen atom to account for water molecule.

3. RESULTS AND DISCUSSION 3.1. Structural interpretation of 1 The asymmetric unit of complex comprises of one and a half unit of Mg(II) ions, three half units of linker NDC, two molecules of dimethylformamide (DMF) and one uncoordinated water molecule. The crystal data and refinement details are summarized in Table 1. Figure 1 illustrates the structure of the compound contains two crystallographically independent Mg2+ cations and are surrounded by organic linker (NDC) and DMF molecules. The organic linker in this MOF exhibits two distinct coordination modes i.e. monodentate and bidentate as


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shown in the scheme 1. The central metal atom Mg1 and Mg2 adopts six coordinated octahedral geometry (Figure 2).

Figure 1. Coordination environment of metal cations in ortep view with 50% probability hydrogen atoms omitted for clarity

Scheme 1. Bonding modes of linker (NDC) in 1



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Table 1. Crystal data, Data collection and Refinement details of 1 Compound Empirical formula Formula weight Wavelength (Å) Space group T(K) a(Å) b(Å) c(Å) α(o) β(o) γ(o) V(Å3) Z ρcal (g/cm3) F(000) µ(MoKα) (mm-1) θ range, deg Index range

[Mg3(NDC)3(DMF)4].H2O C48 H48 Mg3 N4 O17 1023.82 g/mol 1.54180 C2/c 150 13.4191(2) 18.0669(2) 20.9746(3) 90.000(0) 99.66(0) 90.000(0) 5013.03(9) 8 1.35646 2135.5 1.200 4.1-72.4 -12 ≤ h ≤ 16, -21 ≤ k ≤ 22, -25 ≤ l ≤ 23 4715/0/330 16419 0.099 0.346 0.33*0.26*0.20 1.717

Data/restraints/parameter Total reflections R1 [on F02, I > 2σ(I)] wR2 [on F02, I > 2σ(I)] Crystal size (mm) GOOF


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Figure 2. Coordination geometry of 1

Mg1 is bonded by carboxylate oxygen atoms of NDC (O1×2, O3×2, O8×2), whereas Mg2 is bonded by four carboxylate oxygen atoms (O2, O4, O7, O8) from two NDC linker and remaining two oxygen atoms from dimethylformamide (O5, O6). DMF molecules are not seen to be involved in bonding with Mg1. The bond distance of Mg and oxygen atoms of DMF varied slightly [Mg-O5: 1.969(5) Å, Mg-O6: 2.168(3) Å] due to bond orientation. The average Mg-O bond distance of 2.154 Å is validated by earlier reports. Among all these carboxylate oxygen atoms, O8 involved in the bridged bond connecting the adjacent Mg1 and Mg2 metal centers. The trinuclear secondary building unit (SBU) was developed through the chelation of two Mg2 and one Mg1 with oxygen atoms as shown in the Figure 3.



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Figure 3. Representation of the trinuclear SBU cluster in 1 Similar trinuclear moieties of Mg2+ with dicarboxylates have also been reported in the literature.51 Subsequently, Mg1 is connected to two adjacent Mg2 centers to form a linear unit with non-bonding distance of Mg1-Mg2: 3.6459(9) Å. These three Mg2+ ions form linear chains and connected to the six NDC ligands, which lead to the generation of 3D-dimensional architecture. As shown in the Figure 4, the DMF solvent molecules occupy the voids of the MOF, which on removal lead to permanent porosity. The lattice water participates in inter molecular hydrogen bonding [C17-H17C---O101, Symmetry codes: -1/2+x, ½+y, -z] (Figure 5) with DMF molecule, which further strengthens the integrity of the network. The list of bond lengths and bond angles are summarized in Table 2.


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Figure 4. Extended three dimensional structure of 1 viewed along a-axis (DMF molecules within the channels)

Figure 5. Hydrogen bond between oxygen (O101) atom of uncoordinated water and DMF



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Table 2. Selected bond lengths (Å) and angles (°) for 1 Mg1─O1 Mg1─O3 Mg1─O8 Mg2─O2 Mg2─O4 Mg2─O5 Mg2─O6 Mg2─O7 Mg2─O8

2.101(2) 2.098(2) 2.006(3) 2.119(2) 2.086(3) 1.969(5) 2.168(3) 2.122(2) 2.256(2)

O1─Mg1─O3 90.8(1) O1─Mg1─O8 93.84(9) O1─Mg1─O1 91.3(1) O3─Mg1─O8 86.58(9) O3─Mg1─O1 174.3(1) O3─Mg1─O3 87.7(1) O2─Mg2─O4 91.1(1) O2─Mg2─O6 174.7(1) O4─Mg2─O5 105.4(2) O4─Mg2─O8 94.9(9) O5─Mg2─O7 98.8(2) O7─Mg2─O8 59.9(3) Symmetry operators of 1: (i) x,y,z (ii) -x,y,1/2-z (iii) 1/2+x,1/2+y,z (iv)1/2-x,1/2+y,1/2-z (v)-x,-y,-z (vi) x,-y,1/2+z (vii) 1/2-x,1/2-y,-z viii) 1/2+x,1/2-y,1/2+z A FT-IR spectrum reveals that the absorption peak at 1605 cm-1 is due to C=C stretching vibrations of benzene ring. The vibrational frequency at 1667 cm-1 is of C=O stretching of amide group and characteristic peaks at 976 cm-1 and 668 cm-1 indicate the presence of DMF molecules. The appearance of absorption peak at 843 cm-1 shows the out of plane bending vibrations of C-H bond from β-substituted naphthalene. The stretching vibrational frequency at 443 cm-1 indicates the formation of metal to oxygen bond. Figure 6 represents the FT-IR spectrum of 1

Figure 6. FT-IR spectrum of 1 12 ACS Paragon Plus Environment

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3.2. Thermogravimetric analysis Thermogravimetric analysis reveals that MOF 1 is stable up to 350oC. As shown in Figure 7, the first decomposition step observed below 200oC with weight loss of 1.56% (Cald. 1.56%), which indicates the removal of uncoordinated lattice water present in the crystal structure. The second decomposition step appeared between 280 to 320oC which corresponds to removal of DMF molecules with a weight loss of 28.50% (Cald. 29.0%). Third decomposition step between 450 to 580oC indicates the decomposition of 2,6naphthalenedicarboxylate with weight loss of 90.80% (Cald. 89.80%). Finally, MgO only remained beyond 600oC.

Figure 7. TGA curve of 1

3.3. Photoluminescence property The photoluminescence property of alkaline-earth metals has been generally less investigated. Guo et al., and Duraisamy et al., have reported the fluorescent activities of magnesium based MOFs.52,53 In the present study photoluminescence property of 1 along 13 ACS Paragon Plus Environment


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with free ligand was examined in solid state at room temperature. Figure 8 demonstrates that a violet emission for the 1 at 398 nm on excitation at 365 nm, whereas free ligand emits blue emission at 442 nm on same excitation at the same wavelength. The observed blue shift with reduced intensity for the compound as compared to the free ligand may be attributed to the ligand-based electronic transition and enhanced energy gap on coordination.54 These observations suggest that the 1 may prove useful as a fluorescent probe.

Figure 8. PL spectra of (a) 1 (b) free ligand

3.4. Catalytic activity of [Mg3(NDC)3(DMF)4].H2O (1) To assess the activity of the MOF as heterogeneous catalyst, the synthesis of 4H-pyran heterocycle moieties was chosen as reaction of choice. A typical reaction involving 2,5dimethoxy benzaldehyde, malononitrile, and cyanoacetamide was opted for examining the catalytic efficacy of 1 (Scheme 2). Initially, all the reactants in equimolar ratios (1.0 mmol) were mixed in ethanol without any added catalyst. No product formation was observed even 14 ACS Paragon Plus Environment

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after 12 h, both at RT and under reflux conditions. Thereafter, 0.03 mmol of MOF was employed as catalyst for the reaction at RT. In 30 min time, the formation of product was noticed through continuous TLC (thin-layer chromatography) monitoring. After the removal of catalyst by filtration, evaporation of the solvent and washing with ethanol, pure organic product was obtained, with a yield of 96%. Spectral analysis (1H,

13

C and

15

N-NMR)

positively confirmed the product as 2,6-diamino-4-(2,5-dimethoxyphenyl)-4H-pyran-3,5dicarbonitrile. The 1H-NMR signals at δ 3.81, 3.82 were corresponding to the methoxy (OCH3) groups, while signal at δ 7.48 ppm assigned to the amino (-NH2) group. The

15

N

spectrum further confirmed the presence of amino groups in the organic compound (Fig S1S3).

Scheme 2. typical reaction 1

Spectral data of 2,6-Diamino-4-(2,5-dimethoxyphenyl)-4H-pyran-3,5-dicarbonitrile;- H NMR

(400 MHz, DMSO) δ 3.81 (s, 3H, OCH3), 3.82 (s, 3H, OCH3),4.90 (s, 1H, CH), 7.05 (s, 2H, ArH), 7.36 (d, J = 8.25, 1H, ArH), 7.48 ( s, 4H, NH2); 13C NMR (100 MHz, DMSO): 33.9, 56.7, 60.2, 71.5, 111.1, 119.2, 120.7, 121.0, 124.0, 146.2, 152.1, 155.0; 15N NMR (40.55 MHz, DMSO) δ 7.48 (s, 4H, NH2).

Further to select the appropriate solvent for the catalyzed reaction various non-polar and polar solvents were examined. While non-polar solvent like n-hexane, toluene did not carry the reaction, the polar protic solvents, (Me)2CHOH and MeOH produced good yields (Table S1). Ethanol with relative to other protic solvents gave exemplary yields. Afterwards, to



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assess the activity of other catalysts, basic catalysts such as NaOH, Et3N, Na2CO3 etc. were investigated. Reaction gave only trace amounts of product after 6 h. With acidic catalysts like Al2O3, SiO2, and Fe2O3, yields were relatively better than with basic catalysts, but were poor (Table S2).

Thus, MOF 1 assured the excellent yield under otherwise similar conditions. To identify the suitable catalyst loading, different amounts from 0.01 to 0.05 mmol were examined. The 0.03 mmol of catalyst showed a best performance with 96% yield in 30 min. While less than 0.03 mmol gave lesser yields, more than 0.03 mmol, i.e. 0.04 and 0.05 mmol of catalyst produced 92 and 89% yield in 30 and 40 min, respectively (Table S3). The overall optimization results revealed that 0.03 mmol of MOF 1 as catalyst in ethanol at room temperature proved excellent, in terms of both yield and reaction duration, thus proving well suited for the synthesis of 4H-pyran moieties. Further to assess the efficacy of 1, other substituted aldehydes including electron donating and withdrawing were investigated. All reactions were afforded good to excellent yields (Table 3), which establish the viability of 1 as excellent catalyst for synthesis of 4H-pyran derivatives in short reaction time. Development of unsaturated metal centers and void spaces in the framework are the focal points for the selective catalysis.55,56 Upon activation of 1 at temperature range 250-300oC, the solvent molecules were liberated from the crystal structure, as evidenced from the TG analysis and made the central metal atom as coordinatively unsaturated centers. Further, these Mg2+ unsaturated centers act as Lewis acidic sites and push forward the organic reaction to occur selectively. Two possibilities may be ascertained to MOF catalysis, (i) to make substrates more accessible in the pores of MOFs, entrapped solvent, DMF molecules in the pores are removed leaving the channels more free for chemical reactions and (ii) as per the previous studies, in the case of larger substrates, the catalysis occurs only on the external


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surface of the MOF. The unsaturated metal centres are capable to interact with the substrates to catalyze the reaction.24 In the proposed mechanism, initially, unsaturated centers of MOF stimulate and facilitate the Knoevenagel condensation between aldehyde (1) and malononitrile (2) to produce arylidinemalononitrile (3) intermediate. Secondly, the intermediate (3) reacts with cyanoacetamide followed by cyclization and tautomerization, finally to afford the target molecule (Scheme 3).

Table 3. List of synthesis of 4H-pyran moieties with different substituted aromatic aldehydes with [Mg3(NDC)3(DMF)4].H2O as catalyst*,a Entry

aldehyde

Product

Yield (%)

Time(min)

1 94

30

92

30

94

40

2

CHO 3 OMe OH



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4

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93

35

91

40

92

35

5

6

7 94

40

*Reaction conditions: substituted benzaldehyde (1.0 mmol), malononitrile (1.0 mmol), cyanoacetamide (1.0 mmol), 0.03 mmol of [Mg3(NDC)3(DMF)4].H2O as catalyst and ethanol (5.0 mL) at RT a isolated yields


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Scheme 3. Probable mechanism

3.5. Reusability The reusability is one of the prime criteria as far as heterogeneous catalyst is concerned. After the reaction, the MOF 1 was separated from the reaction product by simple filtration and dried. No acute weight difference was observed in the recovered catalyst, which was barely < 1.5 % in each cycle. The activity of filtered catalyst was tested the same typical reaction under otherwise reaction conditions for the successive reactions. The MOF 1 worked 19 ACS Paragon Plus Environment


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efficiently up to six cycles, but marginal decrease in the yield (Figure 9), which is attributed to the recovery efficiency. After sixth cycle, the yield significantly depleted, which showed that the 1 is efficient up to six cycles, suggesting that catalyst is adoptable for valued-organic transformations sustainably.

Figure 9. Recycling studies of 1 as catalyst

4. CONCLUSIONS Use of MOFs as catalysts, minimize the problems associated with separation and recovery of homogeneous catalysts. The Mg(II) based MOF, namely [Mg3(NDC)3(DMF)4].H2O was designed and structurally characterized. The carboxylate oxygen atoms of NDC and DMF molecules were involved in bonding to construct a 3D-dimensional framework architecture. The creation of unsaturated Mg2+ centers up on activation possesses Lewis acidic character, which is useful in the catalyzed organic reactions. The novel 2,6-diamino-4-(2,5-OMe)-4Hpyran-3,5-dicarbonitrile was synthesized by adopting the three-component MCR in the presence of 1 as catalyst. The 96% yield in 30 min reaction time of 2,6-Diamino-4-(2,5dimethoxyphenyl)-4H-pyran-3,5-dicarbonitrile proved the catalyst ability as well as 20 ACS Paragon Plus Environment

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necessary for its employment in the reaction. Further to examine the catalytic nature of 1, other eight substituted aldehydes were made to involve in the reaction and the results were ascribed the superiority of 1 as catalyst. The low cost preparation, reusability up to six cycles of 1 and environmentally benign synthesis of 4H-pyran derivatives in remarkable yields at RT in the presence of 1 makes this novel protocol ideal among the similar ones.

ACKNOWLEDGEMENTS The authors sincerely acknowledge the receipt of financial assistance and research facilities from the National Research Foundation, Pretoria, South Africa, and the University of KwaZulu-Natal, Durban, South Africa respectively.

Supporting Information The CCDC number 998831 contains the information regarding the supplementary crystallographic

data.

These

data

can

be

obtained

free

of

charge

via

www.ccdc.cam.ac.uk/conts/retrieving.html or [from the Cambridge Crystallographic Data Center (CCDC), 12 Union Road, Cambridge CB21 EZ, UK; Fax: +44(0)1223-336,003; Email:[email protected]]. Structure factor table is available from the authors. The catalyst optimization and spectral data of all organic products are incorporated in the supporting information file. This information is available free of charge via the Internet at http://pubs.acs.org/

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Figure Captions Scheme 1. Bonding modes of linker (NDC) in 1 Scheme 2. typical reaction Scheme 3. Probable mechanism



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Figure 1. Coordination environment of metal cations in ortep view with 50% probability hydrogen atoms omitted for clarity Figure 2. Coordination geometry of 1 Figure 3. Representation of the trinuclear SBU cluster in 1 Figure 4. Extended three dimensional structure of 1 viewed along a-axis (DMF molecules within the channels) Figure 5. Hydrogen bond between oxygen (O101) atom of uncoordinated water and DMF Figure 6. FT-IR spectrum of 1 Figure 7. TGA curve of 1 Figure 8. PL spectra of (a) 1 (b) free ligand Figure 9. Recycling studies of 1 as catalyst

Table 1. Crystal data, Data collection and Refinement details of 1 Table 2. Selected bond lengths (Å) and angles (°) for 1 Table 3. List of synthesis of 4H-pyran moieties with different substituted aromatic aldehydes with [Mg3(NDC)3(DMF)4].H2O as catalyst*,a


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Synthesis, structure and properties of new Mg(II)-metal-organic framework and its prowess as catalyst in the production of 4H-pyrans Kranthi Kumar Gangu a, Suresh Maddila a, Saratchandra Babu Mukkamala b, Sreekantha B Jonnalagadda a,* a,

b

* School of Chemistry & Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban 4000, South Africa

Department of Chemistry, GITAM Institute of Science, GITAM University, Visakhapatnam – 530045, Andhra Pradesh, India.

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