Porphyrin based porous organic polymer as bi-functional catalyst for selective oxidation and Knoevenagel condensation reactions

Applied Catalysis A: General 459 (2013) 41–51

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Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata

Porphyrin based porous organic polymer as bi-functional catalyst for selective oxidation and Knoevenagel condensation reactions Arindam Modak, John Mondal, Asim Bhaumik ∗ Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India

a r t i c l e

i n f o

Article history: Received 3 October 2012 Received in revised form 6 March 2013 Accepted 26 March 2013 Available online 15 April 2013 Keywords: Fe-porphyrin Base catalysis Bi-functional catalysis Knoevenagel condensation Porous organic polymer Liquid phase selective oxidation

a b s t r a c t Porphyrin based microporous organic polymer Fe-POP-1 has been synthesized through a facile solvothermal method involving extended aromatic substitution of pyrrole and terephthaldehyde in the presence of Fe(III). This material has very high BET surface area and exhibits two types of catalytic sites: iron-free porphyrin moieties for base catalysis as well as Fe(III)-bound sites for slective oxidation reactions. Due to the presence of basic porphyrin macrocyclic site in Fe-POP-1, it catalyzes Knoevenagel condensation of aromatic aldehydes with malononitrile at room temperature, whereas the Fe(III)-bound site catalyzes selective oxidation of alcohols to the respective aldehyde/ketones in the presence of tert-butyl hydroperoxide (TBHP) as oxidant. Good reusability and excellent selectivity makes this Fe-POP-1 as a promising and efficient bi-functional heterogeneous catalyst for the production of organic fine chemicals through the environmentally benign liquid phase catalytic reactions. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Over the past few decades porous materials have attracted widespread application in many frontline areas of science and technology, and generated immense scientific interests [1,2]. Unlike mesoporous materials with wide pore dimensions [3–6], metal organic framework (MOF) or purely organic frameworks based on micropores with restricted pore dimensions (<2 nm) have attracted much interests in the context of gas adsorption and storage [7,8]. But their potential as catalysts and catalytic supports are much less explored due to instability of their porous structure under humid atmosphere in the liquid and gas phase catalytic reaction conditions [9]. Porous organic polymers with amorphous structures are devoid of such disadvantage as they are much easier to synthesize. Thus, based on this unique structural feature several opportunity lies in microporous polymers and several reactive functional groups can be attached at the surface of this intriguing class of material. Microporous organic polymers that have attracted immense interest in recent times include conjugated microporous polymers (CMPs) [10], polymers of intrinsic microporosity (PIMs) [11], crystalline triazine-based frameworks (CTFs) [12], porous aromatic frameworks (PAFs) [13], and so on. But despite their complicated and tedious synthetic routes, and sometimes very

∗ Corresponding author. Fax: +91 33 2473 2805. E-mail address: [email protected] (A. Bhaumik). 0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2013.03.036

expensive catalysts needed for their synthesis, none of these materials have been explored in bi-functional catalytic reactions [14–17]. Selective oxidation of alcohols to carbonyl compounds is one of the most important fundamental reactions in organic chemistry, since the carbonyl group that produced is an invaluable building block for the synthesis of a variety of organic fine chemicals [18,19]. Conventional methods like Swern or Jones oxidation using stoichiometric amount of inorganic oxidizing agent (i.e., KMnO4 , MnO2 , CrO3 , Br2 , etc.) suffers from huge drawbacks like production of heavy metal wastes, eco-toxicity and poor reusability [20,21]. Heterogeneous catalyst based on Au nanoparticles [22], Pd [23], Au/Pd, Au/Pt [24], Fe [25] nanoparticles or they are dispersed over high surface area carbon or oxide supports [26], Ru and Cu [27] containing catalysts, etc. have been employed to overcome this problem. But the use of heavy toxic metals, high reaction temperatures, leaching of the metallic species from the catalyst surface to the solution, are the major drawbacks of these catalytic systems. Thus, for the development of a green and sustainable catalytic process a robust heterogeneous catalyst, which is highly reactive for the liquid phase selective oxidation reactions under mild reaction conditions in the presence of the peroxide as oxidant is very desirable [28,29]. Similarly, base catalysis is also another fascinating area of research and in this context Knoevenagel condensation has received particular attention. This reaction introduces conjugated double bonds in the aromatic compounds and solid bases like alkali or alkaline-earth-metal oxides [30] are conventionally used as catalyst for this reaction. A number of modifications in the catalyst design have been reported for this

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Scheme 1. Schematic diagram for the formation of microporous Fe-POP-1, where the curved lines are for the extension of polymerization reaction. Because of the presence of two types of catalytic sites, this polymer showed bi-functional catalytic property in the base catalyzed Knoevenagel condensation and selective oxidation of alcohol to aldehyde and ketone.

reaction, which contains both phase transfer catalyst (PTC) [31], pyridine-functionalized porous polymers [32], DABCO based ionic liquid [33], porous coordination polymer [34], cation-exchanged zeolites [35], primary amine functionalized MCM-41 [36] and so on. We have synthesized very high surface area microporous organic polymer Fe-POP-1 containg both Fe-free porphyrin and metalloporphyrin building blocks through hydrothermal treatment of pyrrole with terephthaldehyde in the presence of very small amount of FeCl3 [37]. Here the porphyrin moieties are repeatedly bridged by phenyl linkers leaving behind entrapped Fe(III) sites within the porous skeleton (Scheme 1). Thus, both basic and Fe(III)containing sites are present in the material and these can be utilized in bifunctional catalytic reactions [38]. Mimicking the biological pathways with metalloporphyrin based systems for the development of catalytic process have witnessed an exceptional growth over last few decades [39]. Metalloporphyrins, which are supposed to be used as models for cytochrome P-450 enzyme, catalyzes several oxidation, alkene epoxidation, alkane hydroxylation and so on [40]. Unlike homogeneous metalloporphyrin based systems, which possess inherent difficulty in seperating the catalyst from the reaction mixture together with the cost of the catalyst, supported metalloporphyrin matrices serves advantages like prevention of catalyst from intermolecular self-oxidation, dimerisation of sterically unhindered porphyrins and easy separation from reaction mixture [41,42]. Thus, it is ecologically viable to use the high surface area Fe-POP-1 for selective liquid phase oxidation of alcohols using TBHP as oxidant. In addition remaining basic N-sites of the built-in porphyrin moieties have been employed for the first time as solid phase heterogeneous base catalyst for the Knoevenagel condensation between aromatic aldehyde and malononitrile at room temperature. 2. Experimental Terephthaldehyde was purchased from Sigma–Aldrich. Pyrrole was purchased from SRL, India and distilled prior to use. Glacial acetic acid, TBHP and all other organic solvents were procured from Merck, India and were used after purification. Carbon, hydrogen and nitrogen contents of Fe-POP-1 were determined using a Perkin Elmer 2400 Series II CHN analyser. Loading of Fe in Fe-POP-1 was estimated through chemical analysis by using a

Shimadzu AA-6300 double beam atomic absorption spectrometer (AAS). Fourier Transform Infra Red (FTIR) spectra of the samples were recorded using a Nicolet MAGNA-FT IR 750 Spectrometer Series II. Mass spectrometric data were acquired by the electron spray ionization (ESI) technique at 25–70 eV in a Micromass Qtof-Micro Quadruple mass spectrophotometer. Nitrogen sorption experiments and micropore analysis were conducted at −195.8 ◦ C using Beckman Coulter, SA 3100 instrument. Prior to adsorption measurement the sample was degassed in vacuum at 180 ◦ C for about 3 h. NLDFT pore-size distribution of Fe-POP-1 was obtained using the carbon/slit-cylindrical pore model as reference. The 13 C cross-polarization magic angle spinning (CP-MAS) NMR spectrum was recorded on a Bruker Avance III600WB 600 MHz spectrometer at 150.9 MHz and a MAS frequency of 12 kHz. Thermogravimetry (TGA) and differential thermal analyses (DTA) of the samples were carried out in a TGA Instruments thermal analyser TA-SDT Q-600 under nitrogen atmosphere with heating rate 10◦ /min. EPR measurements were performed on a Bruker EMX EPR spectrometer at X-band frequency (9.46 GHz) at liquid nitrogen temperature (77 K). Transmission electron microscopic (TEM) images of the microporous polymer were recorded by using a JEOL JEM 2010 transmission electron microscope operated at 200 kV. The samples were prepared by dropping a colloidal suspension of the sample obtained after sonicating the sample for 2 min with methanol onto the carbon-coated copper grids. UV–visible diffuse reflectance spectra were recorded on a Shimadzu UV 2401PC spectrophotometer fitted with an integrating sphere attachment and using BaSO4 as background standard. Products of the catalytic reactions were analyzed through the isolated yield and 1 H and 13 C NMR analysis. 1 H and 13 C NMR experiments (liquid state) were carried out on a Bruker DPX-300 NMR spectrometer. 2.1. Synthesis of Fe-POP-1 In a typical experiment in a flame dried round bottom flask freshly distilled pyrrole (0.025 g, 0.37 mmol) was mixed with terephthaldehyde (0.05 g, 0.37 mmol). Then 15 ml glacial acetic acid was added into the mixture with constant stirring along with ferric chloride (0.44 mmol) under inert nitrogen atmosphere. The whole solution was stirred in a magnetic stirrer and after 3 h the mixture was transferred to a Teflon lined autoclave and kept under hydrothermal treatment for 72 h at 180 ◦ C. After 3 days the autoclave was slowly cooled down to room temperature and a dark brownish product was separated out from the reaction mixture. The precipitated solid was filtered and thoroughly washed with distilled water, methanol, acetone, THF and dichloromethane, respectively, and then vacuum dried in an oven at 80 ◦ C for another 48 h. The material was further rigorously washed through Soxhlet extraction for 24 h with water, methanol and tetrahydrofuran (THF), respectively, to give 0.095 g yield of Fe-POP-1. Elemental analysis (%) observed through combustion: C, 77.0; H, 4.3; N, 7.8. Found by EDX analysis (wt%) C, 88.4; N, 2.3. Calcd. Theoretical formula for an infinite unit of Fe-POP-1 is {C44 H26 N4 }n with C, 86.5; H, 4.2; N, 9.2 and n = 1 − ∞. 2.2. Oxidation reaction For the selective oxidation reaction flame dried round bottom flask was charged with substrate alcohol (1 mmol), Fe-POP-1 (20 mg, 0.00004 mmol Fe(III)), 1.5 mmol TBHP (70 wt% in water) in 5 ml CH3 CN and the resulting mixture was stirred in a magnetic stirrer at 70◦ C under nitrogen atmosphere. The progress of the reaction was monitored by TLC using ethyl acetate:hexane (6:4) as eluent. After completion of the reaction, the catalyst was simply filtered and washed thoroughly by diethyl ether and then extracted with a mixture of hexane and diethyl ether. The organic fraction was

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Fig. 1. TEM image of Fe-POP-1.

washed thoroughly by saturated brine solution and dried in presence of anhydrous Na2 SO4 . Removal of the organic solvent under reduced pressure resulted in the oxidized product selectively. The products were purified as before. 2.3. Base catalysis In a typical Knoevenagel condensation reaction, 1.0 mmol of aryl aldehyde, 1.2 mmol of malononitrile and 0.02 g Fe-POP-1 catalyst was mixed in a 50 ml round bottom flask along with absolute ethanol (20 ml). The whole solution was mixed well by a magnetic stirrer and then stirring continued at room temperature. The progress of the reaction was monitored by TLC. After the reaction has been completed, the mixture was filtered and ethanol was removed. The crude product was re-dissolved in ethyl acetate and then washed thoroughly with water and brine. The organic part thus collected was well dried by magnesium sulphate and then the solvent was removed under vacuum to yield organic product, which was further re-crystallized in ethanol. The final products were identified through several spectroscopic analyses and verified from their corresponding authentic data as mentioned in literature. 3. Results and discussion 3.1. Characterizations Detailed synthesis and characterization of Fe-POP-1 material have been described in our previous report [37]. Typical high resolution TEM image of Fe-POP-1 has been shown in Fig. 1. As seen from the image Fig. 1a that spherical particles having dimensions ranging from 100 to 150 nm are distributed throughout the matrices and

some particles are adhere with each other to form large particles. Such uniformly distributed porous nanomaterials are quite unique and particularly interesting for the adsorption and catalytic applications. Further, high resolution transmission electron microscopic image (Fig. 1b) reveals low electron density white spots (pores) of dimensions ca. 0.8–1.0 nm are distributed randomly within the spherical nanoparticles and these are attributed to the microporosity in Fe-POP-1. Fig. 1c and d shows the high magnification images at different portions of the grid. Samples marked by darker contrast showed the presence of white spots (pores) corresponding to the dimension of ca. 1.0 nm. N2 sorption results revealed that Fe-POP-1 has very high BET surface area (875 m2 g−1 ) and pore volume (0.3 cm3 g−1 ), which is comparable with other organic polymers namely conjugated microporous polymers [10], polymers of intrinsic microporosity [11], crystalline triazine-based frameworks [12], phloroglucinol based microporous organic polymer [1] and so on. Pore size distribution plot employing NLDFT model further supported the presence of large micropores in Fe-POP-1 (Fig. S1, supporting information). Large internal void space and surface area helps the easy diffusion of the substrate and product molecules through the active centers located at the internal surface of the porous material [43]. TG–DTA analysis results suggested considerably high thermal stability up to ca. 773 K. Further, heating beyond 773 K caused structural collapse with exothermic peaks in the DTA plot (Fig. S2). Presence of Fe(III)-porphyrin moieties in Fe-POP-1 has been evidenced due appearance of several bands corresponding to 318, 470, 595 and 635 nm (Fig. S3). It is pertinent to mention that presence of porphyrin unit in the Fe-POP-1 is responsible for the appearance of Soret bands (450–474 nm) and Q band (595, 635, 705 nm) [38]. Electron paramagnetic resonance spectra of both

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Scheme 2. Selective oxidation of alcohols to corresponding aldehyde and ketone over Fe-POP-1. Conventional oxidation reactions and oxidation over Pd [23], Au/Pt [24], Ru/Cu [27], Cu/Fe/TEMPO [41] catalytic systems are shown for example.

Fig. 2. Electron paramagnetic resonance spectrum of Fe-POP-1 (black) and the corresponding iron free POP (red). (For interpretation of the references to color in this figure caption, the reader is referred to the web version of the article.)

Fe-POP-1 (black line) and iron-free POP-1 (red line) at 77 K are shown in Fig. 2. Fe-POP-1 exhibits two signal corresponding to g = 4.202 and 1.998, but POP-1 (iron-free) shows only one signal with g = 1.998. Presence of high spin Fe(III) (S = 5/2) has been evidenced from g = 1.998 value without any splitting pattern in the low-field region, whereas the signal for the perpendicular component g⊥ of 4.202 remains un-resolved. This g⊥ value is the characteristic for isolated Fe(III) in axial symmetry, which represents high spin Fe(III) with rhombic distortion [44]. This EPR spectrum of Fe-POP-1 cannot reveal g|| and A|| parameters. Sharp signal appearing at g = 1.99 for iron-free POP-1 is quite unlikely and it seems because of the presence of stable porphyrin radical. Thus g⊥ value of 1.998 as observed in Fe-POP-1 could be attributed to the presence of the metal-free porphyrin moiety as well as high spin species corresponding to the ironporphyrin component. This result suggested Fe-POP-1 possess two types of moieties in the network: iron containing Fe(III)-porphyrin and iron-free porphyrin components. AAS analysis of the material revealed the presence of 0.000267 mmol Fe(III) per g in Fe-POP-1. However, this loading of Fe(III) is much lower than that of one Fe(III) atom per porphyrin unit, which clearly suggests that many of the porphyrin units of Fe-POP-1 are Fe(III)-free and these sites could involve in the base catalyzed reactions. The solid state 13 C CP-MAS NMR spectrum of Fe-POP-1 showed four resonances at chemical shifts of 119.0, 127.7, 131 and 135.0 ppm corresponding to different carbon atoms of the prophyrin rings (Fig. S4). Further, the FTIR analysis revealed the presence of sharp peak at 1001 cm−1 , which could originates due to strong coordination of N–Fe sites in the porous porphyrin network in Fe-POP-1 and this peak is absent in iron-free POP-1 (Fig. S5). 3.2. Catalysis Based on this perspective (high surface area, inbuilt free porphyrin and Fe(III)-porphyrin sites) we have carried out a series of catalytic reactions for the selective oxidation of alcohols. In Scheme 2 we have shown the selective oxidation of various benzyl alcohols over Fe-POP-1 and compared it with the other catalysts conventionally used for this selective oxidation reaction. Our results suggested acetonitrile is the best solvent affording the product benzaldehyde with a yield of 80% when TBHP (70% aqueous) was used as oxidant (Table 1, entry 1). All other organic solvents such as DMF, DMSO, THF, DMAC, NMP are also found to be more or less compatible with acetonitrile. However, selectivity of the reaction is disturbed in the presence of water alone used as a solvent.

Here in addition to aldehydes, some over oxidation product is also formed. Amount of the catalyst has little influence on the yield of the product and 0.02 g catalyst (0.00004 mmol Fe(III)) affords maximum yield with very high TOF. So the net standardized condition is as: for 1 mmol substrate, 0.02 g catalyst, TBHP (1.5 mmol, 70% aqueous) as oxidant, acetonitrile as solvent at 70 ◦ C. With this optimization in hand selective oxidation of a variety of benzyl alcohols has been tested over Fe-POP-1. As shown in Table 1, both electron donating and electron withdrawing benzyl alcohols, ␣-hydroxy ketones, secondary alcohols are efficiently oxidized to respective aldehyde and ketones [45]. Moreover, after prolonging the reaction time (Table 1, entries 1–3) no over oxidation product has been detected, which suggested high selectivity of our catalyst system. Hetero atom substituted substrates like pyrrole-2–methanol, which is highly susceptible to over-oxidation under the present reaction condition gives very good selectivity for the corresponding aldehyde (Table 1, entry 12). Allylic alcohols such as cinamyl alcohol produces cinamaldehye selectively without any epoxide formation and the same has been found true for other secondary alcohols (Table 1, entries 8 and 10), which only requires little longer reaction time for the completion. The highest TOF value of 1022 h−1 and 1095 h−1 for this catalyst has been achieved for oxidation of 4-hydroxy benzyl alcohol and pyrrole-2-methanol. Homogeneous catalysts like OsHCl(CO)(Pi Pr3 )2 and ruthenium complex [46], trichloro isocyanuric acid [47], Cu(II)/Fe(III)-TEMPO [48], Fe(III)/thymine [49], soluble metalloporphyrin [50], etc. showed good catalytic activity for the oxidation of benzyl alcohols. However, the reaction conditions for these oxidation reactions are either very drastic or often uses very expensive metal or difficulty in the separation of the products from the homogeneous metal catalyst. Such homogeneous catalysts are however suffered from repeated reusability and selectivity. We have carried out control experiments in absence of catalyst and TBHP. Our results suggested that the oxidation reactions cannot proceeds either in absence of Fe-POP-1 catalyst or only using TBHP alone instead of the catalyst. Moreover, the catalytic potential of Fe-POP-1 has also been compared with soluble Fe(III) salt using TBHP as oxidant. But poor selectivity, low TOF value, minimum reusability establishes the superiority of our catalytic system over this homogeneous Fe(III) salt. For recycling studies (Fig. S6, supporting information) we have chosen 4-nitro-benzyl alcohol as a representative substrate in the liquid phase oxidation reaction. After completion of the reaction (as confirmed by TLC) the catalyst has been filtered, washed thoroughly and used for three successive cycles. After third cycle, product yield has been decreased marginally from 85% in the first cycle to 79.5%, suggesting good reusability of the Fe-POP-1 catalyst. Further, due to strong covalent binding of Fe(III) center with porphyrin network, no evidence of leaching

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Table 1 Selective oxidation of several alcohols over Fe-POP-1 catalyst.a

OH

OH R R2

R1 OH

R2

Fe-POP-1 (0.02 g) TBHP

R1

R1

R2

O

CH3CN 700C

O

O

CHO

R1

R2 O

Time (h)

Yieldb (%)

TOF (h−1 )

1

14

80

841

2

12

85

689

3

12

85

840

4

13

82

519

5

10

85

1022

6

14

82

714

7

12.5

75

714

8

20

80

297

9

15

82

630

Entry

Substrate

Product

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Table 1 (Continued) Time (h)

Yieldb (%)

TOF (h−1 )

10

14.5

80

472

11

15

82

621

12

12

75

1095

13

18

60

608

14

20

78

318

15

24

75

208.9

16

20

80

333.8

Entry

a b

Substrate

Product

Reaction was carried out using 1 mmol aldehyde, 0.02 g catalyst, TBHP (1.5 mmol, 70% aqueous) in acetonitrile at 70 ◦ C. Yields refer to pure products based on 1 H, 13 C NMR analysis.

of iron in the solution is observed as confirmed through the AAS chemical analysis (no Fe detected) of the filtrate after the completion of the reaction. This result suggested true heterogeneous nature of Fe-POP-1 in liquid phase partial oxidation reaction in the presence of TBHP. Here, in the presence of TBHP, ironhydroxo species [51] could generate at the Fe(III)-sites present at the surface of Fe-POP-1, which could effectively catalyze the oxidation of alcohols to the respective aldehyde/ketones. Detailed mechanistic pathways for Fe-POP-1 catalyzed oxidation have been given in Fig. 3. As shown here, Fe-POP-1 at first reduces TBHP to tert-butylhydroperoxo radical and itself oxidized to Fe(IV)-POP. Alcohol oxidation now takes place with Fe(IV) sites of porphyrin macrocycles with the regeneration of Fe(III)-POP catalyst. In this

oxidation step while alcohol is being oxidized to aldehyde or ketone, oxidation by products like water and hydrogen radical has been produced. This hydrogen radical further recombines with tert-butylhydroperoxo radical and forms tertiary butanol and completes the catalytic cycles [52,53]. Further, the oxidation of 4-nitrobenzylalcohol showed drastic retardation in the presence of radical scavenger ascorbic acid (Table 2, entries 2 and 3). This result suggested that in the presence of TBHP over Fe-POP-1, the selective partial oxidation reaction follows a radical pathway (Fig. 3). Moreover, it is pertinent to mention that many of the MOFs [54] cannot be used in repeated catalytic cycles for liquid phase oxidation reactions due to easy leaching of the coordinated metal

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Fig. 3. Mechanism for Fe-POP-1 catalyzed selective oxidation reactions.

cations from the ligand sites during the reaction, hence collapsing of its porous framework. Our catalytic system is highly robust and reusable in this context, as evidenced from the retention of microporosity and high surface area after three repetitive cycles (Fig. S7: N2 adsorption/desorption isotherm of the reused catalyst). Base catalyzed Knoevenagel condensation reaction has also been carried out over Fe-POP-1, which bears N-sites of the porphyrin rings as active centers. ␣,␤-Unsaturated aromatic dicyanides are very important for designing suitable targeted drug molecules. Several attempts for the modification of the reaction by using different solid phase catalysts have been reported in this context. High temperature treatment of ammonia vapors to calcined silica nanomaterials (SBA-15, MCM-48) produces silicon oxynitride materials (N-SBA-15, N-MCM-48) which have huge potential for carrying out such condensation reactions [55]. Later Ogura et al. have shown how introduction of methyl group to silicon oxynitride largely influence on its basic property [56]. Knoevenagel condensation in neutral atmosphere catalyses by cationic Pd cage complexes by Fujita et al. is also interesting [57]. Again the use of montmorillonite KSF [58] as water stable inorganic solid catalyst for coumarin-3-carboxylic acid synthesis has attracted much attention in this context. All these methods for the synthesis of solid phase catalyst are complicated and summarized in Scheme 3 visá-vis our porous polymer catalyst Fe-POP-1. The catalytic results

are summarized in Table 3 [59]. Our effort by means of simple onepot synthesis of porphyrin embedded solid phase catalyst is quite simple and basic N-sites of the pyrrole moiety in the macrocyclic ring promotes the abstraction of proton from active methylene group of malononitrile to generate carbanion, which subsequently attacks the electrophilic aldehydes to yield the condensation products (Fig. 4). To the best of our knowledge Knoevenagel reaction catalyzed by microporous porphyrin based organic polymer containing secondary amine sites has not yet been explored till date. The initial reaction was carried out using 0.02 g catalyst with respect to the substrate benzaldehyde. Taking into account the green and environmentally benign conditions, room temperature

Scheme 3. Knoevnagel condensation of aromatic aldehydes with malononitrile over Fe-POP-1. This microporous polymeric catalyst is compared with N-MCM-48 [45], Me-N-SBA-15 [46], Pd-cage complex [47] KSF [48] for the same reaction.

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Table 2 Effect of radical scavenger for oxidation of alcohols.a Entry

Alcohol

Time (h)

OH

1

12

2c

CHO

12–24

NO2

3c

12

NO2

CHO

OH

12–24

NO2

c

85

NO2 OH

a

Yieldb (%)

CHO

NO2

b

Product

14

NO2

Reaction was carried out using 1 mmol aldehyde, 0.02 g catalyst, TBHP (1.5 mmol, 70% aqueous) in acetonitrile at 70 ◦ C. Yields refer to pure products based on 1 H, 13 C NMR analysis. In presence of radical scavengers.

and water-ethanol mixed solvent has been chosen for these purposes. It is very difficult for carrying out the condensation reactions in presence of less reactive secondary amine sites. But this difficulty can easily be eliminated over our porphyrin functionalized Fe-POP1 as catalyst. Except 4-carboxy-bezaldehyde (Table 3, entry 4) all the aldehydes show very high yield for the corresponding condensation product. Presence of porphyrin scaffolds in the network of the catalyst could be responsible for its high proton affinity and

thus provide necessary catalytically active basic sites responsible for these condensation reactions. The catalyst has been recycled for six consecutive cycles for the condensation of benzaldehyde and malononitrile. The yield of the condensation product marginally decreased to 95.4% from its first cycle of 99.0% (Fig. S8), suggesting very high catalytic efficacy of Fe-POP-1 in the Knoevenagel condensation reaction at room temperature. High yield of pure products at room temperature, easy separation from reaction mixture by

Fig. 4. Mechanism for free porphyrin sites of Fe-POP-1 catalyzed Knoevenagel condensation.

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Table 3 Knoevenagel condensation of different aromatic aldehydes over Fe-POP-1.a

CN CHO

Fe-POP-1 (0.01g) CN

+ R

Entry

CN

CN

Water/EtOH (1:1) 6-12 h r.t, stirring Aldehyde

Time (h)

Product

Yield (%)

1

6

99

2

4

98

3

10

99

4

12

62

5

6

99

6

6

96

7

12

82

8

8

86

a Reaction performs with 1.0 mmol aldehyde, 1.2 mmol malononitrile in absolute ethanol under room temperature stirring and yield refers to the pure products obtained from 1 H, 13 C NMR analysis.

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simple filtration, high selectivity and reusability of Fe-POP-1 in the Knoevenagel reaction are the major highlights of this work. 4. Conclusion In summary, we have designed high surface area microporous organic polymer bearing porphyrin sites within the porous network through a simple one-pot bottom up approach involving extended aromatic substitution of pyrrole with terephthaldehyde. This material possess both free porphyrin and Fe(III)-porphyrin framework building blocks and thus exhibits bi-functional catalytic property: base catalyzed Knoevenagel condensation and liquid phase selective partial oxidation reactions under mild reaction conditions. Bi-functional catalytic application of Fe-POP-1 reported herein may contribute significantly in the synthesis of targeted organic fine chemicals through eco-friendly catalytic routes. Acknowledgments AM and JM thank CSIR, New Delhi, for their respective senior research fellowships. AB wishes to thank DST, New Delhi for the instrumental support through DST Unit on Nanoscience. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.apcata.2013.03.036. References [1] A.P. Katsoulidis, M.G. Kanatzidis, Chem. Mater. 23 (2011) 1818–1824. [2] Y.C. Zhao, Q.Y. Cheng, D. Zhou, T. Wang, B.H. Han, J. Mater. Chem. 22 (2012) 11509–11514. [3] T. Asefa, M.J. MacLachlan, N. Coombs, G.A. Ozin, Nature 402 (1999) 867–871. [4] M.P. Kapoor, Q. Yang, S. Inagaki, J. Am. Chem. Soc. 124 (2002) 15176–15177. [5] A. Modak, J. Mondal, V.K. Aswal, A. Bhaumik, J. Mater. Chem. 20 (2010) 8099–8106. [6] A. Modak, J. Mondal, M. Sasidharan, A. Bhaumik, Green Chem. 13 (2011) 1317–1331. [7] C. Zlotea, R. Campesi, F. Cuevas, E. Leroy, P. Dibandjo, C. Volkringer, T. Loiseau, G. Ferey, M. Latroche, J. Am. Chem. Soc. 132 (2010) 2991–2997. [8] Y.H. Jin, B.A. Voss, A. Jin, H. Long, R.D. Noble, W. Zhang, J. Am. Chem. Soc. 133 (2011) 6650–6658. [9] A.M. Shultz, O.K. Farha, J.T. Hupp, S.T. Nguyen, J. Am. Chem. Soc. 131 (2009) 4204–4205. [10] J.X. Jiang, F. Su, H. Niu, C.D. Wood, N.L. Campbell, Y.Z. Khimyak, A.I. Cooper, Chem. Commun. 48 (2008) 6–488. [11] M. Carta, K.J. Msayib, P.M. Budd, N.B. McKeown, Org. Lett. 10 (2008) 2641–2643. [12] X. Zhu, C. Tian, S.M. Mahurin, S.H. Chai, C. Wang, S. Brown, G.M. Veith, H. Luo, H. Liu, S. Dai, J. Am. Chem. Soc. 134 (2012) 10478–10484. [13] T. Ben, H. Ren, H.S. Ma, D. Cao, J. Lan, X. Jing, W. Wang, J. Xu, J.F. Deng, J.M. Simmons, S. Qiu, G. Zhu, Angew. Chem. Int. Ed. 48 (2009) 9457–9460. [14] R. Noyori, M. Yamakawa, S. Hashiguchi, J. Org. Chem. 66 (2001) 7931–7944. [15] T. Setoyama, Catal. Today 116 (2006) 250–262. [16] K. Lang, J. Park, S. Hong, J. Org. Chem. 75 (2010) 6424–6435. [17] N. Kondamudia, S.K. Mohapatra, M. Misra, App. Catal. A: Gen. 393 (2011) 36–43. [18] Z. Hu, F.M. Kerton, Appl. Catal. A: Gen. 413–414 (2012) 332–339. [19] A. Villa, M. Plebania, M. Schiavonia, C. Milone, E. Piperopoulos, S. Galvagno, L. Prati, Catal. Today 186 (2012) 76–82. [20] A.J. Mancuso, S.L. Huang, D. Swern, J. Org. Chem. 43 (1978) 2480–2482. [21] C. Wiles, P. Watts, S.J. Haswell, Tetrahedron Lett. 47 (2006) 5261–5264. [22] Y. Yuan, N. Yan, P.J. Dyson, Inorg. Chem. 50 (2011) 11069–11074. [23] X. Ye, M.D. Johnson, T. Diao, M.H. Yates, S.S. Stahl, Green Chem. 12 (2010) 1180–1186. [24] A.F. Lee, C.V. Ellis, K. Wilson, N.S. Hondow, Catal. Today 157 (2010) 243–249. [25] V. Mazumder, M.F. Chi, K.L. More, S.H. Sun, J. Am. Chem. Soc. 132 (2010) 7848–7849. [26] H.Y. Sun, Q. Hua, F.F. Guo, Z.Y. Wang, W.X. Huang, Adv. Synth. Catal. 354 (2012) 569–573. [27] S.G. Babu, P.A. Priyadarsini, R. Karvembu, Appl. Catal. A: Gen. 392 (2011) 218–224. [28] S. Verma, M. Nandi, A. Modak, S.L. Jain, A. Bhaumik, Adv. Synth. Catal. 353 (2011) 1897–1902. [29] S.J. Singh, R.V. Jayaram, Syn. Commun. 42 (2012) 299–308.

[30] S.I. Fujita, B.M. Bhanage, D. Aoki, Y. Ochiai, N. Iwasa, M. Arai, Appl. Catal. A: Gen. 313 (2006) 151–159. [31] J.A. Corona, R.D. Davis, S.B. Kedia, M.B. Mitchell, Org. Process Res. Dev. 14 (2010) 712–715. [32] Y.L. Zhang, S. Liu, S.Y. Liu, F.J. Liu, H.Y. Zhang, Y.Y. He, F.S. Xiao, Catal. Commun. 12 (2011) 1212–1217. [33] D.Z. Xu, Y. Liu, S. Shi, Y.M. Wang, Green Chem. 12 (2010) 514–517. [34] Y. Tan, Z. Fu, J. Zhang, Inorg. Chem. Commun. 14 (2011) 1966–1970. [35] S. Saravanamurugan, M. Palanichamy, M. Hartmann, V. Murugesan, Appl. Catal. A: Gen. 298 (2006) 8–15. [36] J. Mondal, A. Modak, A. Bhaumik, J. Mol. Catal. A: Chem. 335 (2011) 236–241. [37] A. Modak, M. Nandi, J. Mondal, A. Bhaumik, Chem. Commun. 48 (2012) 248–250. [38] L. Chen, Y. Yang, D. Jiang, J. Am. Chem. Soc. 132 (2010) 9138–9143. [39] T.C. Bruice, Acc. Chem. Res. 24 (1991) 243–249. [40] B. Meunier, Chem. Rev. 92 (1992) 1411–1456. [41] F.L. Benedito, S. Nakagaki, A.A. Saczk, P.G.P. Zamora, C.M.M. Costa, Appl. Catal. A: Gen. 250 (2003) 1–11. [42] J. Haber, L. Matachowski, K. Pamin, J. Połtowicz, Catal. Today 91–92 (2004) 195–198. [43] N. Pal, M. Paul, A. Bhaumik, Appl. Catal. A: Gen. 393 (2011) 153–160. [44] A.L. Faria, C. Airoldi, F.G. Doro, M.G. Fonseca, M.D. Assis, Appl. Catal. A: Gen. 268 (2004) 217–226. [45] Spectroscopic data (1 H and 13 C NMR) for oxidation of alcohols as given in Table 1. Entry 1: (Benzaldehyde) 1 H NMR (300 MHz, CDCl3 ) ı = 8.13 (d, 2H, ArH, J = 7.12 Hz), 7.64 (m, 1H, ArH), 7.50 (2H, d, ArH, J = 7.8 Hz), 10.2 (s, 1H, CHO) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 190, 143, 134, 130.9, 130.3 ppm. Entry 2: (4-nitro benzaldehyde) 1 H NMR (300 MHz, CDCl3 ) ı = 10.16 (s, 1H, CHO), 8.41 (2H, d, J = 8.6 Hz), 8.09 (2H, d, J = 8.7 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 190, 148, 130, 127, 124, 123.8 ppm Entry 3: (4-Fluoro benzaldehyde)1 H NMR (300 MHz, CDCl3 ) ı = 9.9 (s, 1H, CHO), 7.6 (2H, d, J = 8.5 Hz), 7.4 (2H, d, J = 8.6 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 191, 168, 134, 133, 114 ppm Entry 4: (4-bromo benzaldehyde) 1 H NMR (300 MHz, CDCl3 ) ı = 9.8 (s, 1H, -CHO), 7.4 (2H, d, J = 8 Hz), 7.5 (2H, d, J = 8Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 190, 128, 132, 134, 131 ppm. Entry 5: (4-hydroxy benzaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.85 (s, 1H, CHO), 7.82 (d, 2H, J = 8.5 Hz), 6.99 (d, 2H, J = 8.5 Hz), 6.6 (s, 1H, OH) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 191, 161, 132, 129, 116 ppm Entry 6: (3Fluoro benzaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.87 (s, 1H, CHO), 7.6 (s, 1H, ArH), 7.4 (m, 3H) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 190, 143,160, 132, 127 ppm Entry 7: (3-chloro benzaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.97 (s, 1H, CHO), 7.84 (s, 1H, ArH), 7.76 (d, 1H, J = 7.5 Hz), 7.49 (m, 2H, ArH) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 189, 140, 136, 130, 127 ppm. Entry 8: (Benzil) 1 H NMR (500 MHz, CDCl3 ) ı = 7.98 (d, 4H, J J = 8.5 Hz, ArH), 7.68 (t, 2H, 8 Hz), 7.53 (t, 2H, J = 7.5 Hz) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 130, 136, 134, 188, 132 ppm. Entry 9: (Cinamaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.69 (dd, J = 2.5 Hz, 8 Hz, 1H, CHO), 6.72 (ddd, J = 2, 8, 16 Hz, CH), 7.47 (m, 1H, CH), 7.55 (m, ArH, 2H), 7.38 (m, ArH, 3H) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 193.7, 152, 134, 131, 129, 128, 77 ppm. Entry 10: (Benzophenone) 1 H NMR (500 MHz, CDCl3 ) ı = 7.82 (d, J = 12 Hz, ArH), 7.50 (t, J = 12.79 Hz, ArH), 7.61 (t, 2H, J = 12.1 Hz) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 130, 137, 128, 132, 185 ppm. Entry 11: (Terephthaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 10.3 (s, 2H, CHO), 8.03 (s, 4H, ArH) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 192, 140, 130.3 ppm. Entry 12: (Pyrrole-2carbaxaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.5 (s, 1H, CHO), 6.35 (m, 1H), 7.00 (s, 1H), 7.16 (s, 1H) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 179.5, 126, 121, 111.5, 132 ppm. Entry 13: (Cyclohexanone) 1 H NMR (500 MHz, CDCl3 ) ı = 2.14 (d, 4H, J = 6.5 Hz), 1.66 (m, 6H) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 211, 41.5, 26.6, 24.6 ppm. Entry 14: (3,4,5-trimethoxybenzaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.84 (s, 1H, CHO), 7.106 (s, 1H, ArH), 3.95 (s, 9H, OCH3 ) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 191, 153.7, 143, 131, 106, 61, 56 ppm. Entry 15: (3methoxy-4-benzoxybenzaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 9.83 (s, 1H, CHO), 3.94 (s, 3H, OCH3 ), 5.24 (s, 2H, CH2 ), 7.33 (4H, m, ArH), 6.99 (d, 1H, J = 8.5 Hz), 7.44 (m, 2H, ArH), 7.31 (s, 1H, ArH) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 56.2, 71, 109.5, 112, 136, 130, 128, 127, 150, 153, 191 ppm. Entry 16: (napthalene-1-carboxaldehyde) 1 H NMR (500 MHz, CDCl3 ) ı = 10.4 (s, 1H, CHO), 9.26 (d, 1H, J = 8.5 Hz, ArH), 8.11 (d, 1H, J = 7.5 Hz, ArH), 8.00 (d, 1H, J = 7 Hz, ArH), 7.934 (d, 1H, J = 8.5 Hz, ArH), 7.63 (m, 3H, ArH) ppm. 13 C NMR (125 MHz, CDCl3 ) ı = 193, 136, 135, 133, 131, 130, 129, 128, 127, 125 ppm. [46] J. Tauchman, B. Therrien, G.S. Fink, P. Stepnicka, Organometallics 31 (2012) 3985–3994. [47] M.A. Zolfigol, F. Shirini, A.G. Choghamarani, Synthesis (2006) 2043–2046. [48] N. Wang, R. Liu, J. Chen, X. Liang, Chem. Commun. (2005) 5322–5324. [49] A.A. Hunaiti, T. Niemi, A. Sibaouih, P. Pihko, M. Leskela, T. Repo, Chem. Commun. 46 (2010) 9250–9252. [50] M. Hajimohammadi, N. Safari, H. Mofakham, F. Deyhimi, Green Chem. 13 (2011) 991–997. [51] M.J. Park, J. Lee, Y. Suh, J. Kim, W. Nam, J. Am. Chem. Soc. 128 (2006) 2630–2634. [52] K. Chen, L. Que, J. Am. Chem. Soc. 123 (2001) 6327–6337. [53] E.C. McLaughlin, H. Choi, K. Wang, G. Chiou, M.P. Doyle, J. Org. Chem. 74 (2009) 730–738. ˛ [54] J. Zakzeskia, A. Debczak, P.C.A. Bruijnincx, B.M. Weckhuysen, Appl. Catal. A: Gen. 394 (2011) 79–85. [55] Y. Xia, R. Mokaya, Angew. Chem. Int. Ed. 42 (2003) 2639–2644. [56] K. Sugino, N. Oya, N. Yoshie, M. Ogura, J. Am. Chem. Soc. 133 (2011) 20030–20032. [57] T. Murase, Y. Nishijima, M. Fujita, J. Am. Chem. Soc. 134 (2012) 162–164. [58] F. Bigi, L. Chesini, R. Maggi, G. Sartori, J. Org. Chem. 64 (1999) 1033–1035.

A. Modak et al. / Applied Catalysis A: General 459 (2013) 41–51 [59] Spectroscopic data (1 H and 13 C NMR chemical shifts) for different condensation products of ␣,␤-unsaturated di cyano compounds as given in Table 3: Entry 1: 1 H NMR (300 MHz, CDCl3 ) ı = 7.85 (2H, ArH, d, J = 7.47 Hz), 7.71 (1H, s, CH), 7.59 (1H, ArH, t, J = 7.296 Hz), 7.50 (2H, ArH, d, J = 7.77 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 160, 134.7, 131, 130.8, 129.7, 113.7, 83.03 ppm. Entry 2: 1 H NMR (300 MHz, CDCl3 ) ı = 8.73 (2H, ArH, d, J = 8.736 Hz), 8.08 (2H, ArH, d, J = 8.72 Hz), 7.88 (s, CH) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 156.9, 135.9, 131.4, 124.7, 112.7, 11.7, 87.7 ppm. Entry 3: 1 H NMR (500 MHz, CDCl3 ) ı = 8.44 (1H, s, CH), 8.36 (1H, d, ArH, J = 8 Hz), 7.89 (1H, d, ArH, J = 8 Hz), 7.82 (2H, t, ArH, J = 7.5 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 158.7, 135, 133.52,130.6, 129.2, 128.2, 126.8, 112.3 ppm. Entry 4: 1 H NMR (300 MHz, DMSO-d6 ) ı = 7.93 (2H, d, ArH, J = 8.37 Hz),

51

8.03 (2H, d, ArH, J = 8.4 Hz), 8.20 (1H, s, CH) ppm. 13 C NMR (75 MHz, DMSO-d6 ) ı = 170, 128, 130, 140, 129, 165, 82, 121 ppm. Entry 5: 1 H NMR (300 MHz, CDCl3 ) = 7.74 (1H, s, CH), 7.24 (2H, d, ArH, J = 8.51 Hz), 7.98 (2H, d, ArH, J = 8.77 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 162, 115, 127, 132, 165, 84, 120 ppm. Entry 6: 1 H NMR (300 MHz, CDCl3 ) ı = 7.86 (2H, d, ArH, J = 8.55 Hz), 7.73 (1H, s, CH), 7.53 (2H, d, ArH, J = 8.6 Hz) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 158.4, 141.2, 131.9, 130.2, 129.4, 113.5, 83.5 ppm. Entry 7: 1 H NMR (300 MHz, DMSO-d6 ) ı = 8.10 (4H, s, ArH), 8.66 (2H, s, CH) ppm. 13 C NMR (75 MHz, DMSO-d6 ) ı = 160.3, 135.9, 131.4, 130.5, 114.3, 113.3, 85.3 PPM. Entry 8: 1 H NMR (500 MHz, CDCl3 ) ı = 7.88 (2H, d, Ar-H, J = 4 Hz), 7.22 (1H, t, Ar-H, J = 4.5 Hz), 7.81 (s, CH) ppm. 13 C NMR (75 MHz, CDCl3 ) ı = 164, 136, 125,127.3, 130, 85, 120 ppm.