Novel magnetic nanoparticles Fe3O4-immobilized domino Knoevenagel

ShortCommunicationNovel magnetic nanoparticles Fe 3O 4-immobilized domino Knoevenagel condensation,Michael addition,and cyclization catalystAmin Rostami ⁎,Bahareh Atashkar,Hoshyar GholamiDepartment of Chemistry,Faculty of Science,University of Kurdistan,Zip Code 66177-15175,Sanandaj,Irana b s t r a c ta r t i c l e i n f o Article history:Received 11January 2013Received in revised form 15March 2013Accepted 20March 2013Available online 27March 2013Keywords:Magnetic nanoparticles GuanidineBasic nanocatalystKnoevenagel condensation Chromene derivativesThe synthesis,characterization and applications of guanidine supported on magnetic nanoparticles Fe 3O 4(MNPs –Guanidine)as a novel magnetically separable base nanocatalyst are described.We have studied the application of this new catalyst for the Knoevenagel condensation reaction of aromatic aldehydes with malononitrile or cyanoacetate in PEG/water =1:1at room temperature.Also,the three-component and one-pot synthesis of 2-amino-4H -chromenes and 2-amino-4H -benzo[h ]chromenes by condensing al-dehydes,malononitrile and cyclic 1,3-dicarbonyl/α-naphthol,in the presence of catalytic amount of MNPs –Guanidine under same conditions is investigated.The supported catalyst could simply be separated and recovered from the reaction mixture with the assistance of an external magnet and reused several times.©2013Elsevier B.V.All rights reserved.1.IntroductionRecently,magnetic nanoparticles have been extensively employed as alternative catalyst supports,in view of their high surface area resulting in high catalyst loading capacity,high dispersion,outstanding stability,and convenient catalyst recycling [1,2].Magnetic separation renders the recovery of catalysts from liquid-phase reactions much easier than by cross-flow filtration and centrifugation.In addition,the magnetic properties of the particles are stable enough to tolerate most chemical environ-ments,with the exception of those that are extremely acidic or corrosive.Guanidines are important classes of compound that are found throughout nature that also have many uses within organic chemistry commonly as organic bases [3].However the major disadvantage of catalysts based on guanidine is their separation from the products which needs solid –liquid or liquid –liquid techniques in many reac-tions.This drawback can be overcome by immobilizing these catalysts on magnetic nanoparticle (MNPs),which can be easily removed from the reaction mixture by magnetic separation.In continuation of our research program to develop selective,ef ficient and green methods and catalysts in organic synthesis [4–6],here we report the preparation and characterization of MNPs –Guanidine as a novel,eco-friendly,recoverable and reusableorganic –inorganic hybrid catalyst for the synthesis of α,β-unsaturated carbonyl compounds and chromene (2H -1-benzopyran)derivatives via Knoevenagel condensation,Michael addition,and cyclization reactions.The biological,pharmaceutical,medicinal,and therapeu-tic properties of α,β-unsaturated carbonyl compounds [7]and chromene derivatives [8]have been well established in the litera-ture.Although,there are many synthetic route to synthesis of these valuable compounds [9–31]but,improvement of catalytic route in terms of environmentally benign and economical approach is highly desirable.2.Experimental2.1.General procedure for the Knoevenagel condensationsThe MNPs –Guanidine (0.005g,0.39mol%)was added to a mixture of malononitrile (0.066g,1mmol)or ethylcyanoacetate (0.113g,1mmol)and aldehyde (1mmol)in PEG/water =1:1(2ml),and then the mixture was stirred at room temperature for the appropriate time.The progress was monitored by TLC.After completion of the re-action,the catalyst was separated from the product by exposure to an external magnet (within 5s).The reaction mixture was decanted and extracted with (3×5ml)diethyl ether.The evaporation of diethyl ether under reduced pressure gave the pure products in 94–98%yields.2.2.General procedure for the synthesis of chromene derivativesMNPs –Guanidine (0.03g,2.34mol%)was added to a mixture of dimedone (0.140g,1mmol)or 1,3-cyclohexanedione (0.112g,Catalysis Communications 37(2013)69–74⁎Corresponding author.Tel.:+989183730910;fax:+988716624004.E-mail address:a_rostami372@ (A.Rostami).1566-7367/$–see front matter ©2013Elsevier B.V.All rights reserved./10.1016/j.catcom.2013.03.022Contents lists available at SciVerse ScienceDirectCatalysis Communicationsj o u r n a l h om e p a g e :ww w.e l s e v i e r.c o m /l o c a t e /c a t c o m1mmol)or α-naphthol (0.144g,1mmol)and aldehyde (1mmol)in PEG/water =1:1(2ml),and stirred at room temperature for 10min.Then,malononitrile (0.066g,1mmol)was added to this mixture and stirred at room temperature for the appropriate time.The progress was monitored by TLC.After completion of the reaction,the catalyst was separated from the product by exposure to an external magnet (within 5s).The reaction mixture was decanted and extracted with (3×5ml)diethyl ether.The evaporation of diethyl ether under reduced pressure gave the pure products in 87–98%yields.3.Results and discussions3.1.Preparation and characterization of MNPs –GuanidineThe MNPs –Guanidine was prepared by the concise route outlined in Scheme 1.Naked magnetic Fe 3O 4nanoparticles were prepared through chemical coprecipitation method,and subsequently were coated with 3-chloropropyltrimethoxysilane (CPTMS)to achieve chloropropyl-functionalized magnetic nanoparticles.Ultimately,the reaction of chloropropyl group with guanidine led to the corre-sponding guanidine supported on magnetic nanoparticles (MNPs –Guanidine).Experimental details were provided in the Supplemen-tary data.The characterization of the catalyst was carried out by SEM,XRD,TGA,FT-IR,EDX and VSM (see supplementary data).The SEM image of MNPs –Guanidine was con firmed that the cata-lyst was made up of uniform nanometer sized particles less than 17nm (Fig.S1).The position and relative intensities of all peaks in the XRD pat-tern of MNPs –Guanidine con firm well with standard XRD pattern of Fe 3O 4,indicating retention of the crystalline cubic spinel structure during functionalization of MNPs (Fig.S2,Table S1).An additional broad peak in the XRD pattern of MNPs –Guanidine at 2θ=18–27°is attributed to the amorphous silica shell formed around the mag-netic core [32].The TGA was used to determine the percent of organic functional groups chemisorbed onto the surface of magnetic nanoparticle.The TGA curve of the MNPs –Guanidine shows a weight loss about 10%FeCl 3.6H 2O +FeCl 2.4H 2OMNPs-CPTMS MNPs-guanidineNNH 2NH 2NH 2OH N 2, rt, 30 min(3-chloropropyl) triethoxysilane ethanol/water, 40 °C, 8 hScheme 1.Synthesis of MNPs –Guanidine.+ArCHO X = CN, CO 2EtMNPs-Guanidine (Cat.)CN XXNC Ar H123a-o PEG/H 2O = 1:1, r.t.O ArNH 2CNOR RO OR RMNPs-Guanidine (Cat.)PEG/H 2O = 1:1, r.t.5a-m4R= Me, H OHONH 2ArCNCN CN+67a-f ArCHO orScheme 2.MNPs –Guanidine catalyses the Knoevenagel condensations and the synthesis of the chromene derivatives.70 A.Rostami et al./Catalysis Communications 37(2013)69–74from 260to 600°C,resulting from the decomposition of organic ma-terials grafting to the MNPs surface (Fig.S3).On the basis of this re-sult,the well grafting of guanidinylpropyl groups on the MNPs is veri fied.EDX spectrum shows the elemental composition (N,Si and Fe)of the MNPs –Guanidine (Fig.S4).Successful functionalization of the MNPs can be inferred from FT-IR techniques.The FTIR spectrum of MNPs –Guanidine shows peaks (Fig.S5,1447,1665and 3389cm −1bands)that are characteristic of a func-tionalized guanidine group,which clearly differs from that of the unfunctionalized Fe 3O 4nanomagnets (MNPs)and 3-chloropropylsilica-functionalized magnetic nanoparticles (MNPs-CPTMS).Magnetization curve (Fig.S6)measured at room temperature showed that MNPs –Guanidine is superparamagnetic (Ms =47.4emu g −1,Mr =1.01emu g −1and Hc =14.32Oe).As expected,the Ms value of MNPs –Guanidine compared to the bare MNPs (74.3emu g −1)is de-creased due to the silica coating and the layer of the grafted catalyst.As result,MNPs –Guanidine is readily dispersible in water and can be ef ficiently attracted with a small magnet.All together,the aforemen-tioned results con firmed the formation of a silica layer around the Fe 3O 4nanoparticles and the guanidine-functionalization of this core –shell structure.Unfortunately,due to the magnetic properties of MNPs –Guanidine it is actually impossible to further characterize this material by using solid-state NMR spectroscopy.Detailed inves-tigation of XRD,TGA,FTIR and VSM is discussed and presented in Supplementary data.3.2.The catalytic applications of MNPs –Guanidine in Knoevenagel con-densations and the synthesis of chromene derivativesThe catalytic activity of MNPs –Guanidine was investigated in vari-ous base catalyzed organic transformations like Knoevenagel condensa-tions for the synthesis of arylidene malononitriles and arylidene ethylcyanoacetate and domino Knoevenagel condensation/Michael ad-dition/cyclization reactions for the synthesis of 2-amino-4H-chromenes and 2-amino-4H -benzo[h ]chromenes (Scheme 2).To obtain best catalytic activity,reaction conditions were optimized by evaluating the in fluence of different amounts of catalyst in various solvents on the model reactions in terms of time and product yield (Ta-bles S2and S3).The reactions did not proceed in the absence of catalyst even after prolonged reaction time (entry 1,Tables S2and S3).5and 30mg of catalyst were found to be ideal for the Knoevenagel condensa-tions and the synthesis of chromene derivatives respectively,and about solvent,the best results were obtained using PEG/water =1:1as solvent.As can be seen from Tables 1and 2,the catalytic system worked exceedingly well in both Knoevenagel condensations and synthesis of chromene derivatives with wide range of substrates under theCHONO 271A.Rostami et al./Catalysis Communications 37(2013)69–7472 A.Rostami et al./Catalysis Communications37(2013)69–74optimized reaction conditions.The expected products were obtained in short times and in good to high yields.Surprisingly,we found that this catalyst demonstrated excellent re-coverability and reusability.The catalyst can be ef ficiently recoveredeasily and rapidly from the product by exposure to an external magnet (Fig.1).The separated catalyst was reused for 20and 10runs in the model reactions of Knoevenagel condensations (Fig.2)and synthesis of chromene derivatives (Table S4,Supplementary data)respectively,without any signi ficant loss of its activity.In order to establish the catalytic activity of MNPs –Guanidine and greenness of this method,we compared our results on the synthesis of benzylidene malonitrile with data from the literature (Table 3).4.ConclusionIn summary,we have synthesized the first MNPs –Guanidine for the use as a magnetically heterogeneous basic nanocatalyst.The cat-alyst is easily synthesized and can catalyze the synthesis of arylidene malonates,arylidene cyanoacetates and chromene derivatives via the Knoevenagel condensation,Michael addition,and cyclization with good to high yields in PEG/water at room conditions.The characteris-tic aspects of this catalyst are rapid,simple and ef ficient separation by using an appropriate external magnet,which minimizes the loss ofFig.1.Image showing MNPs –Guanedine can be separated by applied magnetic field.Fig.2.The recycling experiment of MNPs –Guanidine for Knoevenagel condensations of malononitrile (1mmol)and benzaldehyde (1mmol),in PEG/water at room temperature for 5min.73A.Rostami et al./Catalysis Communications 37(2013)69–74catalyst during separation and reusable for several times without any significant loss of activity.AcknowledgmentWe are grateful to the University of Kurdistan Research Councils for the partial support of this work.Appendix A.Supplementary dataSupplementary data to this article 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Catalyst[ref.]Condition Yield(%)Time(min)Number of recycling Loading of catalyst1MNPs–guanidine PEG/H2O,r.t.975Up to2010%2Guanidine[17]CH2Cl2,r.t.70.81200–3Ni-nanoparticles[16]EtOH,r.t.98205Not reported4[Promim]CF3COO[12]CH3CN,80°C9814404–5PANPF-3[18]EtOH,reflux92601016%6Na2S/Al2O3[10]CH2Cl2,reflux90200–7IL@Silica gel[19]SF,100°C93.12404Not reported8Task-specific-IL[13]SF,80°C90.9b15Not reported9p-HAP300/hydroquinone[20]MW or SF,81°C87210–74 A.Rostami et al./Catalysis Communications37(2013)69–74。