Application of a Keplerate type giant nanoporous isopolyoxomolybdate as a reusable catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles

Article abstract of DOI:10.1016/S1872-2067(14)60174-1

The Keplerate-type giant nanoporous isopolyoxomolybdate (NH₄)₄₂[Mo^VI₇₂Mo^V₆₀O₃₇₂-(CH₃COO)₃₀(H₂O)₇₂], denoted {Mo₁₃₂}, has been used as a catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by the one-pot, four-component thermal reaction of benzil with aromatic aldehydes, primary amines, and ammonium acetate under solvent-free conditions. The catalyst was prepared according to a previously published literature procedure using inexpensive and readily available starting materials, and subsequently characterized by FT-IR, UV and X-ray diffraction spectroscopy, as well as microanalysis. The results showed that {Mo₁₃₂} exhibited high catalytic activity towards the synthesis of 1,2,4,5-tetrasubstituted imidazoles, with the desired products being formed in good to high yields. Furthermore, the catalyst was recyclable and could be reused at least three times without any discernible loss in its catalytic activity. Overall, this new catalytic method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles provides rapid access to the desired compounds following a simple work-up procedure, and avoids the use of harmful organic solvents. This method therefore represents a significant improvement over the methods currently available for the synthesis of tetrasubstituted imidazoles.

Full text of DOI:10.1016/S1872-2067(14)60174-1

ChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767
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ꢀ ꢀ ꢀ
ꢀ ꢀ ꢀ ꢀ
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
ꢀ
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
ꢀ
ꢀ
Article
ApplicationꢀofꢀaꢀKeplerateꢀtypeꢀgiantꢀnanoporousꢀ ꢀ
isopolyoxomolybdateꢀasꢀaꢀreusableꢀcatalystꢀforꢀtheꢀsynthesisꢀofꢀ
1,2,4,5‐tetrasubstitutedꢀimidazolesꢀ
AhmadꢀNakhaei,ꢀAbolghasemꢀDavoodniaꢀ*
ꢀ
DepartmentꢀofꢀChemistry,ꢀMashhadꢀBranch,ꢀIslamicꢀAzadꢀUniversity,ꢀMashhad,ꢀIranꢀ
A R T I C L E ꢀ I N F O ꢀ
A B S T R A C T ꢀ
Articleꢀhistory:ꢀ
Theꢀ Keplerate‐typeꢀ giantꢀ nanoporousꢀ isopolyoxomolybdateꢀ (NH
4
)
42[MoVI72MoV60
372
O ‐
Receivedꢀ21ꢀAprilꢀ2014ꢀ
Acceptedꢀ9ꢀJuneꢀ2014ꢀ
Publishedꢀ20ꢀOctoberꢀ2014ꢀ
(CH
3
COO)30(H O)72],ꢀ denotedꢀ {Mo132},ꢀ hasꢀ beenꢀ usedꢀ asꢀ aꢀ catalystꢀ forꢀ theꢀ synthesisꢀ of
2
1,2,4,5‐tetrasubstitutedꢀimidazolesꢀbyꢀtheꢀone‐pot,ꢀfour‐componentꢀthermalꢀreactionꢀofꢀbenzilꢀwithꢀ
aromaticꢀ aldehydes,ꢀ primaryꢀ amines,ꢀ andꢀ ammoniumꢀ acetateꢀ underꢀ solvent‐freeꢀ conditions.ꢀ Theꢀ
catalystꢀwasꢀpreparedꢀaccordingꢀtoꢀaꢀpreviouslyꢀpublishedꢀliteratureꢀprocedureꢀusingꢀinexpensiveꢀ
andꢀ readilyꢀ availableꢀ startingꢀ materials,ꢀ andꢀ subsequentlyꢀ characterizedꢀ byꢀ FT‐IR,ꢀ UVꢀ andꢀ X‐rayꢀ
diffractionꢀspectroscopy,ꢀasꢀwellꢀasꢀmicroanalysis.ꢀTheꢀresultsꢀshowedꢀthatꢀ{Mo132}ꢀexhibitedꢀhighꢀ
catalyticꢀ activityꢀ towardsꢀ theꢀ synthesisꢀ ofꢀ 1,2,4,5‐tetrasubstitutedꢀ imidazoles,ꢀ withꢀ theꢀ desiredꢀ
productsꢀbeingꢀformedꢀinꢀgoodꢀtoꢀhighꢀyields.ꢀFurthermore,ꢀtheꢀcatalystꢀwasꢀrecyclableꢀandꢀcouldꢀbeꢀ
reusedꢀatꢀleastꢀthreeꢀtimesꢀwithoutꢀanyꢀdiscernibleꢀlossꢀinꢀitsꢀcatalyticꢀactivity.ꢀOverall,ꢀthisꢀnewꢀ
catalyticꢀmethodꢀforꢀtheꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀprovidesꢀrapidꢀaccessꢀtoꢀtheꢀ
desiredꢀcompoundsꢀfollowingꢀaꢀsimpleꢀwork‐upꢀprocedure,ꢀandꢀavoidsꢀtheꢀuseꢀofꢀharmfulꢀorganicꢀ
solvents.ꢀThisꢀmethodꢀthereforeꢀrepresentsꢀaꢀsignificantꢀimprovementꢀoverꢀtheꢀmethodsꢀcurrentlyꢀ
availableꢀforꢀtheꢀsynthesisꢀofꢀtetrasubstitutedꢀimidazoles.ꢀ
Keywords:ꢀ
GiantꢀNanoporousꢀ
ꢀ
isopolyoxomolybdateꢀ
Keplerateꢀ
Solvent‐freeꢀconditionꢀ
1,2,4,5‐tetrasubstitutedꢀimidazoleꢀ
©ꢀ2014,ꢀDalianꢀInstituteꢀofꢀChemicalꢀPhysics,ꢀChineseꢀAcademyꢀofꢀSciences.
PublishedꢀbyꢀElsevierꢀB.V.ꢀAllꢀrightsꢀreserved.
1
.ꢀ ꢀ Introductionꢀ
synthesisꢀ ofꢀ nanotubularꢀ materialsꢀ containingꢀ POMsꢀ suchꢀ asꢀ
POM‐basedꢀ titaniumꢀ nanotubesꢀ [5]ꢀ andꢀ POM‐organicꢀ hybridꢀ
nanotubesꢀ[6].ꢀTheseꢀnewꢀtypesꢀofꢀnanotubesꢀpossessꢀtheꢀfunc‐
tionalꢀpropertiesꢀofꢀPOMsꢀasꢀwellꢀasꢀsomeꢀofꢀtheꢀkeyꢀadvantagesꢀ
associatedꢀ withꢀ tubularꢀ systems,ꢀ including,ꢀ forꢀ example,ꢀ en‐
hancedꢀcatalyticꢀandꢀphotochemicalꢀpropertiesꢀ[5–7].ꢀ
Müllerꢀ etꢀ al.ꢀ [8]ꢀ famouslyꢀ reportedꢀ theꢀ discoveryꢀ ofꢀ giantꢀ
nanosizedꢀ porousꢀ Keplerate‐typeꢀ POMs.ꢀ Theꢀ Keplerateꢀ andꢀ
giantꢀ nanosizedꢀ porousꢀ POMsꢀ possessꢀ uniqueꢀ featuresꢀ andꢀ
propertiesꢀthatꢀcouldꢀallowꢀthemꢀtoꢀbeꢀconsideredꢀasꢀtheꢀbasisꢀ
forꢀ aꢀ newꢀ areaꢀ ofꢀ nanochemistryꢀ andꢀ nanomaterialsꢀ scienceꢀ
[9,10].ꢀTheseꢀmaterialsꢀhaveꢀalsoꢀfoundꢀnumerousꢀapplicationꢀ
inꢀ fundamentalꢀ andꢀ appliedꢀ sciences,ꢀ whereꢀ theyꢀ haveꢀ beenꢀ
Polyoxometalatesꢀ (POMs)ꢀ areꢀ aꢀ largeꢀ classꢀ ofꢀ metalꢀ oxideꢀ
clusterꢀ compoundsꢀ consistingꢀ ofꢀ transitionꢀ metalꢀ atomsꢀ
bridgedꢀbyꢀoxygenꢀatoms.ꢀPOMsꢀcanꢀexistꢀinꢀaꢀvarietyꢀofꢀdiffer‐
entꢀsizeꢀandꢀstructure,ꢀandꢀcompoundsꢀbelongingꢀtoꢀthisꢀclassꢀ
haveꢀbeenꢀstudiedꢀextensivelyꢀbecauseꢀtheyꢀpossessꢀinterestingꢀ
electronicꢀandꢀmolecularꢀproperties,ꢀsuchꢀasꢀwide‐rangingꢀre‐
doxꢀ potentials,ꢀ acidities,ꢀ polarities,ꢀ andꢀ solubilities.ꢀ Basedꢀ onꢀ
theirꢀattractiveꢀproperties,ꢀPOMsꢀhaveꢀalsoꢀbeenꢀusedꢀinꢀaꢀvari‐
etyꢀ ofꢀ differentꢀ application,ꢀ includingꢀ catalysis,ꢀ biomedicine,ꢀ
magnetism,ꢀnanotechnologyꢀandꢀmaterialsꢀscienceꢀ[1–4].ꢀThereꢀ
hasꢀ beenꢀ aꢀ growingꢀ interestꢀ duringꢀ theꢀ lastꢀ fewꢀ yearsꢀ inꢀ theꢀ
*ꢀCorrespondingꢀauthor.ꢀTel:ꢀ+98‐511‐8435000;ꢀFax:ꢀ+98‐511‐8424020;ꢀE‐mail:ꢀadavoodnia@mshdiau.ac.ir,ꢀadavoodnia@yahoo.comꢀ ꢀ
DOI:ꢀ10.1016/S1872‐2067(14)60174‐1ꢀ|ꢀhttp://www.sciencedirect.com/science/journal/18722067ꢀ|ꢀChin.ꢀJ.ꢀCatal.,ꢀVol.ꢀ35,ꢀNo.ꢀ10,ꢀOctoberꢀ2014ꢀ ꢀ ꢀ

1762ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
usedꢀtoꢀmodelꢀpassiveꢀcationꢀtransportꢀthroughꢀmembranes,ꢀasꢀ
wellꢀasꢀbeingꢀevaluatedꢀinꢀtermsꢀofꢀtheirꢀencapsulation,ꢀnano‐
separationꢀchemistry,ꢀmagneticꢀandꢀopticalꢀpropertiesꢀ[11,12].ꢀ
Despiteꢀtheirꢀmanyꢀvaluableꢀproperties,ꢀthereꢀhas,ꢀtoꢀtheꢀbestꢀofꢀ
ourꢀknowledge,ꢀbeenꢀonlyꢀoneꢀreportꢀinꢀtheꢀliteratureꢀpertain‐
ingꢀ toꢀ theꢀ useꢀ ofꢀ giantꢀ nanosizedꢀ porousꢀ POMsꢀ asꢀ catalysts,ꢀ
whereꢀ theyꢀ wereꢀ usedꢀ toꢀ catalyzeꢀ theꢀ epoxidationꢀ ofꢀ olefinsꢀ
[
13].ꢀFurthermore,ꢀthereꢀhaveꢀbeenꢀnoꢀreportsꢀconcerningꢀtheꢀ
useꢀofꢀPOMsꢀasꢀcatalystsꢀforꢀmulticomponentꢀreactions.ꢀ
Theꢀ imidazoleꢀ ringꢀ systemꢀ isꢀ anꢀ importantꢀ nitrogen‐
ꢀ
con‐
2.9 nm
tainingꢀsubstructureꢀthatꢀplaysꢀanꢀimportantꢀroleꢀinꢀnumerousꢀ
biochemicalꢀprocesses,ꢀandꢀthisꢀsystemꢀcanꢀbeꢀfoundꢀinꢀaꢀlargeꢀ
numberꢀ ofꢀ naturalꢀ productsꢀ andꢀ pharmacologicallyꢀ activeꢀ
compoundsꢀ [14].ꢀ Multisubstitutedꢀ imidazolesꢀ areꢀ biologicallyꢀ
active,ꢀandꢀseveralꢀcompoundsꢀcontainingꢀsystemsꢀofꢀthisꢀtypeꢀ
haveꢀbeenꢀreportedꢀtoꢀpossessꢀinterestingꢀbiologicalꢀproperties,ꢀ
includingꢀ antibacterialꢀ [15],ꢀ analgesicꢀ [16]ꢀ andꢀ glucagonꢀ re‐
ceptorꢀantagonismꢀ[17]ꢀactivity.ꢀSeveralꢀsubstitutedꢀimidazolesꢀ
haveꢀalsoꢀbeenꢀreportedꢀasꢀinhibitorsꢀofꢀp38ꢀMAPꢀkinaseꢀ[18]ꢀ
andꢀB‐Rafꢀkinaseꢀ[19].ꢀFurthermore,ꢀrecentꢀadvancesꢀinꢀgreenꢀ
chemistryꢀandꢀorganometallicꢀcatalysisꢀhaveꢀextendedꢀtheꢀap‐
plicationꢀ ofꢀ imidazolesꢀ asꢀ ionicꢀ liquidsꢀ [20–22]ꢀ andꢀ
N‐heterocyclicꢀcarbenesꢀ[23].ꢀDespiteꢀtheꢀavailabilityꢀofꢀaꢀwideꢀ
varietyꢀofꢀsyntheticꢀroutesꢀforꢀtheꢀconstructionꢀofꢀimidazoles,ꢀ
Fig.ꢀ1.ꢀStructureꢀofꢀ{Mo132}.ꢀ
nmꢀ basedꢀ onꢀ theoreticalꢀ calculationsꢀ [8,9].ꢀ Polarzꢀ etꢀ al.ꢀ [10]ꢀ
wereꢀtheꢀfirstꢀgroupꢀtoꢀreportꢀtheꢀcharacterizationꢀofꢀtheꢀmo‐
lybdenumꢀclusterꢀusingꢀTEM.ꢀTheꢀTEMꢀpictureꢀclearlyꢀshowedꢀ
thatꢀtheꢀclustersꢀpossessedꢀaꢀperiodicꢀstructureꢀwithꢀanꢀaverageꢀ
diameterꢀ ofꢀ approximatelyꢀ 3ꢀ nm.ꢀ Thisꢀ experimentallyꢀ deter‐
minedꢀ diameterꢀ wasꢀ inꢀ goodꢀ agreementꢀ withꢀ theꢀ theoreticalꢀ
valueꢀforꢀtheꢀinnerꢀdiameterꢀofꢀtheꢀball‐shapedꢀPOMꢀ[8,9].ꢀ
2.ꢀ ꢀ Experimentalꢀ ꢀ
2.1.ꢀ ꢀ SynthesisꢀofꢀtheꢀKeplerateꢀ{Mo132}ꢀ
veryꢀfewꢀmethodsꢀexistꢀforꢀtheꢀsynthesisꢀofꢀ1,2,4,5‐
tutedꢀimidazoles.ꢀTheseꢀcompoundsꢀareꢀgenerallyꢀsynthesizedꢀ
viaꢀ theꢀ four‐componentꢀ reactionꢀ ofꢀ 1,2‐diketonesꢀ orꢀ α‐hy‐
droxyketonesꢀwithꢀaldehydes,ꢀprimaryꢀamines,ꢀandꢀammoniumꢀ
acetateꢀ inꢀ theꢀ presenceꢀ ofꢀ aꢀ catalystꢀ suchꢀ asꢀ L‐prolineꢀ [24],ꢀ
ꢀ
tetrasubsti‐
N
2
H
4
·H
Mo
162.2ꢀmmol)ꢀinꢀH
stirredꢀforꢀ10ꢀmin,ꢀduringꢀwhichꢀtimeꢀitꢀbecameꢀblue‐greenꢀinꢀ
color.ꢀTheꢀmixtureꢀwasꢀthenꢀtreatedꢀwithꢀ50%ꢀCH COOHꢀ (83ꢀ
2
SO
4
ꢀ (0.8ꢀ g,ꢀ 6.1ꢀ mmol)ꢀ wasꢀ addedꢀ toꢀ aꢀ solutionꢀ ofꢀ
Oꢀ(5.6ꢀg,ꢀ4.5ꢀmmol)ꢀandꢀCH COONH ꢀ(12.5ꢀg,ꢀ
Oꢀ(250ꢀml),ꢀandꢀtheꢀresultingꢀsolutionꢀwasꢀ
(NH
4
)
6
7
O24·4H
2
3
4
ꢀ
2
3
K
5
CoW12
O
40.3H
2
Oꢀ [25],ꢀ NH
ionicꢀ liquidꢀ [27],ꢀ BF ‐SiO2ꢀ [28],ꢀ carbon‐basedꢀ solidꢀ acidꢀ [29],ꢀ
InCl .3H Oꢀ [30],ꢀ NaHSO /SiO ꢀ [31],ꢀ H 62.24H O/SiO
32],ꢀFeCl /montmorilloniteꢀK10ꢀunderꢀmicrowaveꢀirradiationꢀ
33],ꢀp‐dodecylbenzenesulfonicꢀacidꢀ[34],ꢀandꢀmontmorilloniteꢀ
4
H
2
PO
4
/Al
2
O
3
ꢀ[26],ꢀ Brönstedꢀacidicꢀ
ml)ꢀ toꢀ giveꢀ aꢀ greenꢀ solution,ꢀ whichꢀ wasꢀ storedꢀ inꢀ anꢀ openꢀ
500‐mlꢀErlenmeyerꢀflaskꢀatꢀ20ꢀ°Cꢀwithoutꢀstirring.ꢀItꢀisꢀnote‐
worthyꢀ thatꢀ theꢀ solutionꢀ becameꢀ darkꢀ brownꢀ inꢀ colorꢀ onꢀ
standing.ꢀFollowingꢀ4ꢀdꢀofꢀstorageꢀunderꢀtheseꢀconditions,ꢀtheꢀ
mixtureꢀ wasꢀ filteredꢀ toꢀ giveꢀ red‐brownꢀ crystals,ꢀ whichꢀ wereꢀ
washedꢀ sequentiallyꢀ withꢀ absoluteꢀ ethanolꢀ andꢀ diethylꢀ ether,ꢀ
beforeꢀbeingꢀdriedꢀinꢀairꢀ[8].ꢀ
3
3
2
4
2
6 2 18
P W O
2
2
ꢀ
[
[
3
K10ꢀsupportedꢀtitaniumꢀ[35].ꢀ1,2,4,5‐Tetrasubstitutedꢀimidaz‐
olesꢀcanꢀalsoꢀbeꢀaccessedꢀbyꢀtheꢀhetero‐Copeꢀrearrangementꢀorꢀ
theꢀN‐alkylationꢀofꢀtrisubstitutedꢀimidazolesꢀ[36,37].ꢀHowever,ꢀ
someꢀofꢀtheseꢀsyntheticꢀmethodsꢀhaveꢀbeenꢀlimitedꢀinꢀtermsꢀofꢀ
theirꢀ applicationꢀ becauseꢀ ofꢀ poorꢀyieldsꢀorꢀtheirꢀ requirementꢀ
forꢀ expensiveꢀ catalysts,ꢀ longꢀ reactionꢀ time,ꢀ andꢀ tediousꢀ isola‐
tionꢀprocedures.ꢀWithꢀthisꢀinꢀmind,ꢀthereꢀisꢀthereforeꢀanꢀurgentꢀ
needꢀ forꢀ theꢀ developmentꢀ ofꢀ aꢀ newꢀ environmentallyꢀ friendlyꢀ
methodꢀusingꢀanꢀinexpensiveꢀcatalystꢀwithꢀhighꢀcatalyticꢀactiv‐
ityꢀforꢀtheꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazoles.ꢀ
Asꢀ aꢀ resultꢀ ofꢀ ourꢀ interestꢀ inꢀ theꢀ synthesisꢀ ofꢀ heterocyclicꢀ
compoundsꢀ [38–41],ꢀ andꢀ asꢀ partꢀ ofꢀ ourꢀ ongoingꢀ researchꢀ to‐
wardsꢀ theꢀ developmentꢀ ofꢀ environmentallyꢀ friendlyꢀ methodsꢀ
forꢀtheꢀsynthesisꢀofꢀorganicꢀcompoundsꢀusingꢀreusableꢀcatalystsꢀ
2.2.ꢀ ꢀ Generalꢀprocedureꢀforꢀtheꢀsynthesisꢀofꢀ
1,2,4,5‐tetrasubstitutedꢀimidazolesꢀ5a–5mꢀ
Aꢀ mixtureꢀ ofꢀ benzilꢀ 1ꢀ (1ꢀ mmol),ꢀ aromaticꢀ aldehydeꢀ 2ꢀ (1ꢀ
mmol),ꢀ primaryꢀ amineꢀ 3ꢀ (1ꢀ mmol),ꢀ ammoniumꢀ acetateꢀ 4ꢀ (1ꢀ
mmol),ꢀandꢀ{Mo132}ꢀ(0.1ꢀg)ꢀwasꢀheatedꢀinꢀtheꢀoilꢀbathꢀatꢀ140ꢀ°Cꢀ
forꢀ20–90ꢀmin.ꢀUponꢀcompletionꢀofꢀtheꢀreaction,ꢀasꢀdeterminedꢀ
byꢀthin‐layerꢀ chromatographyꢀ (TLC),ꢀtheꢀmixtureꢀwasꢀdilutedꢀ
withꢀhotꢀethanolꢀandꢀthenꢀfilteredꢀtoꢀremoveꢀtheꢀcatalyst.ꢀTheꢀ
catalystꢀwasꢀthenꢀwashedꢀwithꢀaꢀsmallꢀportionꢀofꢀhotꢀethanolꢀ
(10ꢀml),ꢀandꢀtheꢀcombinedꢀfiltratesꢀwereꢀconcentratedꢀinꢀvol‐
umeꢀ(byꢀhalf)ꢀandꢀallowedꢀtoꢀstandꢀatꢀroomꢀtemperatureꢀuntilꢀ
precipitationꢀoccurred.ꢀTheꢀresultingꢀprecipitateꢀwasꢀcollectedꢀ
byꢀ filtration,ꢀ andꢀ recrystallizedꢀ fromꢀ ethanolꢀ toꢀ giveꢀ com‐
poundsꢀ5a–5mꢀinꢀhighꢀyieldsꢀ(Schemeꢀ1).ꢀTheꢀmeltingꢀpointsꢀ
wereꢀ recordedꢀ usingꢀ aꢀ Stuartꢀ SMP3ꢀ meltingꢀ pointꢀ apparatus.ꢀ
TheꢀFT‐IRꢀspectraꢀofꢀtheꢀproductsꢀwereꢀrecordedꢀonꢀaꢀTensorꢀ
[
42–48],ꢀweꢀreportꢀhereinꢀtheꢀuseꢀofꢀtheꢀKeplerateꢀtypeꢀgiantꢀ
nanoporousꢀ isopolyoxomolybdate,ꢀ (NH
CH COO)30(H O)72],ꢀ denotedꢀ asꢀ {Mo132}ꢀ (Fig.ꢀ 1),ꢀ asꢀ aꢀ novelꢀ
catalystꢀ forꢀ theꢀ efficientꢀ solvent‐freeꢀ synthesisꢀ ofꢀ 1,2,4,5‐
tetrasubstitutedꢀ imidazoles.ꢀ Thisꢀ newꢀ processꢀ allowsꢀ forꢀ theꢀ
one‐potꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀbyꢀtheꢀ
) O372‐ꢀ
42[MoVI72MoV60
4
(
3
2
ꢀ
ꢀ
four‐componentꢀ condensationꢀ ofꢀ benzilꢀ (1)ꢀ withꢀ anꢀ aromaticꢀ
aldehydeꢀ(2),ꢀprimaryꢀamineꢀ(3),ꢀandꢀammoniumꢀacetateꢀ(4).ꢀ
Theꢀdiameterꢀofꢀthisꢀball‐shapedꢀPOMꢀwasꢀreportedꢀtoꢀbeꢀ2.9ꢀ
27ꢀBrukerꢀspectrophotometerꢀasꢀKBrꢀdisks.ꢀTheꢀ
HꢀNMRꢀspec‐
1
traꢀ wereꢀ recordedꢀ onꢀ Brukerꢀ 400ꢀ andꢀ 500ꢀ spectrometersꢀ atꢀ
400ꢀandꢀ500ꢀMHz,ꢀrespectively.ꢀ

ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
1763ꢀ
{
Mo132
}
O
O
N
N
+
ArCHO
+
RNH2
+
CH COONH
Ar
3
4
Solvent-free
2
3
4
40 oC
R
1
1
5a-5m
Schemeꢀ1.ꢀ{Mo132}ꢀcatalyzedꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazoles.ꢀ
3
.ꢀ ꢀ Resultsꢀandꢀdiscussionꢀ
revealedꢀ fiveꢀ diffractionꢀ peaksꢀ atꢀ 2θꢀ =ꢀ 19.3218°,ꢀ 25.8040°,ꢀ
0.2125°,ꢀ 44.1001°,ꢀ andꢀ 50.2848°.ꢀ Furthermore,ꢀ elementalꢀ
analysisꢀ ofꢀ theꢀ {Mo132}ꢀ catalystꢀ gaveꢀ satisfactoryꢀ data,ꢀ whichꢀ
correspondedꢀ toꢀ aꢀ molecularꢀ formulaꢀ ofꢀ C60 ꢀ
3
3.1.ꢀ ꢀ Characterizedꢀresultsꢀofꢀ{Mo132}ꢀ
H
402Mo132
N O
42 504
Theꢀ {Mo132}ꢀ catalystꢀ wasꢀ characterizedꢀ byꢀ FT‐IR,ꢀ UV/Vis,ꢀ
(Calcd.:ꢀCꢀ3.21%,ꢀHꢀ1.81%,ꢀNꢀ2.62%;ꢀfound:ꢀCꢀ3.30%,ꢀHꢀ1.92%,ꢀ
Nꢀ2.49%).ꢀ
andꢀ X‐rayꢀ diffractionꢀ (XRD)ꢀ spectroscopy,ꢀ asꢀ wellꢀ asꢀ microa‐
nalysis.ꢀTheꢀFT‐IRꢀspectrumꢀofꢀtheꢀcatalystꢀisꢀshownꢀinꢀFig.ꢀ2(1)ꢀ
andꢀcontainsꢀtheꢀcharacteristicꢀvibrationalꢀbandsꢀofꢀtheꢀMo=Oꢀ
3.2.ꢀ ꢀ Evaluationꢀofꢀcatalyticꢀactivityꢀofꢀ{Mo132}ꢀtowardsꢀtheꢀ ꢀ
reactionꢀ
–
1
–
bondꢀatꢀ969ꢀandꢀ936ꢀcm ,ꢀasꢀwellꢀbandsꢀbelongingꢀtoꢀtheꢀCOO ꢀ
+
ꢀ
–1
andꢀ NH
4
ꢀ groupsꢀ at 1544ꢀ andꢀ 1406ꢀ cm ,ꢀ respectively.ꢀ Theꢀ
FT‐IRꢀ spectrumꢀ ofꢀ theꢀ catalystꢀ alsoꢀ containedꢀ bandsꢀ atꢀ
Theꢀ catalyticꢀ activityꢀ ofꢀ {Mo132}ꢀ wasꢀ evaluatedꢀ inꢀ theꢀ syn‐
thesisꢀ ofꢀ 1,2,4,5‐tetrasubstitutedꢀ imidazoles.ꢀ Theꢀ synthesisꢀ ofꢀ
compoundꢀ 5bꢀ byꢀ theꢀ four‐componentꢀ reactionꢀ ofꢀ benzilꢀ (1ꢀ
mmol)ꢀwithꢀ4‐chlorobenzaldehydeꢀ(1ꢀmmol),ꢀanilineꢀ(1ꢀmmol),ꢀ
andꢀ ammoniumꢀ acetateꢀ (1ꢀ mmol)ꢀ wasꢀ initiallyꢀ selectedꢀ asꢀ aꢀ
modelꢀ reactionꢀ toꢀ optimizeꢀ theꢀ reactionꢀ conditions.ꢀ Severalꢀ
reactionꢀ parametersꢀ wereꢀ evaluatedꢀ duringꢀ thisꢀ optimizationꢀ
stage,ꢀincludingꢀtheꢀloadingꢀofꢀtheꢀ{Mo132}ꢀcatalyst,ꢀtheꢀtemper‐
atureꢀofꢀtheꢀreaction,ꢀandꢀtheꢀreactionꢀsolventꢀ(Tableꢀ1).ꢀItꢀisꢀ
clearꢀfromꢀtheꢀresultsꢀshownꢀinꢀTableꢀ1ꢀthatꢀtheꢀshortestꢀreac‐
tionꢀtimeꢀandꢀbestꢀyieldꢀwereꢀachievedꢀunderꢀsolvent‐freeꢀcon‐
ditionsꢀ(Tableꢀ1,ꢀentryꢀ14).ꢀTheseꢀresultsꢀalsoꢀrevealedꢀthatꢀtheꢀ
loadingꢀofꢀtheꢀcatalystꢀandꢀtheꢀreactionꢀtemperatureꢀhadꢀaꢀsig‐
nificantꢀimpactꢀonꢀtheꢀyieldꢀofꢀcompoundꢀ5bꢀwhenꢀtheꢀreactionꢀ
wasꢀconductedꢀunderꢀsolvent‐freeꢀconditions.ꢀForꢀexample,ꢀtheꢀ
reactionꢀgaveꢀaꢀveryꢀlowꢀyieldꢀofꢀtheꢀproductꢀwhenꢀitꢀwasꢀcon‐
–1
2500–3600ꢀ andꢀ 1618ꢀ cm ,ꢀ whichꢀ indicatedꢀ theꢀ presenceꢀ ofꢀ
water.ꢀ Pleasingly,ꢀ theꢀ FT‐IRꢀ spectrumꢀ ofꢀ theꢀ {Mo132}ꢀ catalystꢀ
preparedꢀ inꢀ theꢀ currentꢀ studyꢀ wasꢀ consistentꢀ withꢀ thoseꢀ re‐
portedꢀbyꢀMüller’ꢀ[8]ꢀandꢀZhou’ꢀ[9]ꢀgroups.ꢀTheꢀUV/Visꢀspec‐
trumꢀofꢀ theꢀ{Mo132}ꢀcatalystꢀ providedꢀ furtherꢀconfirmationꢀofꢀ
itsꢀ structure,ꢀ andꢀ theꢀ characteristicꢀ absorptionꢀ bondsꢀ atꢀ 213,ꢀ
232,ꢀ265,ꢀandꢀ447ꢀnmꢀwereꢀconsistentꢀwithꢀthoseꢀreportedꢀinꢀ
theꢀliteratureꢀ[8].ꢀTheꢀXRDꢀpatternꢀofꢀ{Mo132}ꢀcatalystꢀ(Fig.ꢀ3)ꢀ
(
4)
3)
(
(2)
(1)
Tableꢀ1ꢀ
Optimizationꢀofꢀreactionꢀconditionsꢀforꢀsynthesisꢀofꢀcompoundꢀ5bꢀcat‐
alyzedꢀbyꢀ{Mo132}.ꢀ
Catalystꢀ
g)ꢀ
—ꢀ
Timeꢀ
(min)ꢀ yieldꢀ(%)
Isolatedꢀ
Entryꢀ
Solventꢀ
T/°Cꢀ
(
4
000 3500 3000 2500 2000 1500 1000 500
1ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
140ꢀ
r.t.ꢀ
120ꢀ
120ꢀ
ꢀ 90ꢀ
ꢀ 90ꢀ
ꢀ 90ꢀ
ꢀ 90ꢀ
ꢀ 90ꢀ
ꢀ 75ꢀ
ꢀ 90ꢀ
ꢀ 80ꢀ
ꢀ 60ꢀ
ꢀ 80ꢀ
ꢀ 60ꢀ
ꢀ 50ꢀ
ꢀ 50ꢀ
ꢀ 60ꢀ
300ꢀ
300ꢀ
300ꢀ
300ꢀ
30ꢀ
—ꢀ
1
Wavenumber (cm )
2
ꢀ
0.10ꢀ
0.04ꢀ
0.04ꢀ
0.04ꢀ
0.06ꢀ
0.06ꢀ
0.06ꢀ
0.08ꢀ
0.08ꢀ
0.08ꢀ
0.10ꢀ
0.10ꢀ
0.10ꢀ
0.10ꢀ
0.15ꢀ
0.10ꢀ
0.10ꢀ
0.10ꢀ
0.10ꢀ
Fig.ꢀ2.ꢀFT‐IRꢀspectraꢀofꢀtheꢀfreshꢀcatalystꢀ{Mo132}ꢀ((1),ꢀfirstꢀrun),ꢀandꢀthe
recoveredꢀcatalystꢀ((2–4),ꢀrunsꢀ2–4).
3ꢀ
4ꢀ
100ꢀ
120ꢀ
140ꢀ
100ꢀ
120ꢀ
140ꢀ
100ꢀ
120ꢀ
140ꢀ
100ꢀ
120ꢀ
140ꢀ
150ꢀ
150ꢀ
refluxꢀ
refluxꢀ
refluxꢀ
refluxꢀ
59ꢀ
67ꢀ
85ꢀ
70ꢀ
82ꢀ
86ꢀ
74ꢀ
87ꢀ
89ꢀ
81ꢀ
90ꢀ
97ꢀ
96ꢀ
96ꢀ
11ꢀ
31ꢀ
43ꢀ
traceꢀ
5
ꢀ
6
ꢀ
7
ꢀ
8
ꢀ
9
ꢀ
10ꢀ
11ꢀ
12ꢀ
13ꢀ
14ꢀ
15ꢀ
16ꢀ
17ꢀ
18ꢀ
19ꢀ
20ꢀ
2
H Oꢀ
1
0
20
30
40
2
50
60
70
80
CH
CH
CH
3
OHꢀ
o
/( )
3
CH
CNꢀ
2
OHꢀ
Fig.ꢀ3.ꢀXRDꢀpatternꢀofꢀ{Mo132}.ꢀ
3

1764ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
ductedꢀinꢀtheꢀabsenceꢀofꢀtheꢀcatalystꢀatꢀ140ꢀ°Cꢀ(Tableꢀ1,ꢀentryꢀ
),ꢀandꢀgaveꢀnoꢀproductꢀwhenꢀitꢀwasꢀconductedꢀinꢀtheꢀpresenceꢀ
creaseꢀinꢀtheꢀyieldꢀofꢀtheꢀproductꢀ5b,ꢀalthoughꢀfurtherꢀincreasesꢀ
inꢀ theseꢀ parametersꢀ didꢀ notꢀ leadꢀ toꢀ furtherꢀ improvementsꢀ inꢀ
theꢀproductꢀyieldꢀorꢀreactionꢀtimeꢀ(Tableꢀ1,ꢀentriesꢀ15ꢀandꢀ16).ꢀ
Withꢀtheꢀoptimizedꢀconditionsꢀinꢀhand,ꢀweꢀproceededꢀtoꢀex‐
ploreꢀ theꢀ scopeꢀ ofꢀ thisꢀ {Mo132}‐catalyzedꢀ reactingꢀ ofꢀ 1ꢀ andꢀ 4ꢀ
withꢀaꢀrangeꢀofꢀotherꢀaromaticꢀaldehydesꢀ2ꢀandꢀprimaryꢀaminesꢀ
3ꢀ(Tableꢀ2).ꢀAsꢀshownꢀinꢀTableꢀ2,ꢀtheꢀ{Mo132}ꢀcatalystꢀefficientlyꢀ
1
ofꢀtheꢀcatalystꢀatꢀroomꢀtemperatureꢀ(Tableꢀ1,ꢀentryꢀ2).ꢀTheseꢀ
resultsꢀ thereforeꢀ highlightedꢀ theꢀ importanceꢀ ofꢀ theꢀ catalystꢀ
loadingꢀandꢀreactionꢀtemperatureꢀonꢀtheꢀsuccessꢀofꢀtheꢀreac‐
tion.ꢀIncreasesꢀinꢀtheꢀamountꢀofꢀtheꢀcatalystꢀandꢀreactionꢀtem‐
peratureꢀ upꢀ toꢀ 0.10ꢀ gꢀ andꢀ 140ꢀ °C,ꢀ respectively,ꢀ ledꢀ toꢀ anꢀ in‐
Tableꢀ2ꢀ
Synthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀ5a–5mꢀusingꢀtheꢀ{Mo132}ꢀcatalyst.ꢀ
Timeꢀ ꢀ
Isolatedꢀyieldꢀ ꢀ
Meltingꢀpointꢀ(°C)ꢀ
Entryꢀ
Arꢀ
Rꢀaꢀ
Productꢀbꢀ
ꢀ
(min)ꢀ
(%)
Foundꢀ
Reportedꢀ
1ꢀ
6 5
C H ꢀ
6 5
C H ꢀ
5aꢀ
70ꢀ
93ꢀ
213–216ꢀ
216–218ꢀ[28]
N
N
2
ꢀ
4‐ClC
6
H
4
ꢀ
ꢀ
C
6
H
5
ꢀ
5bꢀ
5cꢀ
50ꢀ
60ꢀ
97ꢀ
92ꢀ
153–155ꢀ
189–192ꢀ
149–151ꢀ[28]
187–189ꢀ[25]
N
N
Cl
3ꢀ
4‐ClC
6
H
4
4‐ClC
6
H ꢀ
4
N
N
Cl
Cl
4
ꢀ
4‐ClC
6
H
4
ꢀ
C
6
H
5
CH2ꢀ
CH2ꢀ
5dꢀ
5eꢀ
60ꢀ
60ꢀ
90ꢀ
88ꢀ
160–162ꢀ
170–173ꢀ
162–165ꢀ[28]
172–175ꢀ[26]
N
N
Cl
5ꢀ
4‐BrC
6
H
4
ꢀ
C
6
H
5
N
N
Br
6
ꢀ
4‐MeC
6
H
4
ꢀ
C
6
H
5
ꢀ
5fꢀ
75ꢀ
60ꢀ
91ꢀ
92ꢀ
188–190ꢀ
192–194ꢀ
189–190ꢀ[26]
188–191ꢀ[25]
N
CH3
N
7ꢀ
4‐MeC
6
H
4
ꢀ
4‐MeC
6
H
4
ꢀ
5gꢀ
N
N
CH3
CH3
8ꢀ
6 4
4‐MeC H ꢀ
6 5
C H CH2ꢀ
5hꢀ
70ꢀ
93ꢀ
168–170ꢀ
167–168ꢀ[24]
N
N
CH3
9
ꢀ
4‐MeOC
6
H
4
ꢀ
C
6
H
5
CH
2
ꢀ
5iꢀ
5jꢀ
90ꢀ
30ꢀ
86ꢀ
94ꢀ
159–161ꢀ
191–193ꢀ
161–162ꢀ[26]
192–194ꢀ[34]
N
OCH3
N
10ꢀ
4‐O NC
2 6
H
4
ꢀ
C
6
5
H ꢀ
N
NO2
N
11ꢀ
12ꢀ
13ꢀ
4‐BrC
6
H
4
ꢀ
Meꢀ
Meꢀ
5kꢀ
5lꢀ
75ꢀ
90ꢀ
30ꢀ
88ꢀ
89ꢀ
93ꢀ
200–202ꢀ
222–224ꢀ
242–244ꢀ
202–203ꢀ[26]
222–223ꢀ[24]
248–250ꢀ[33]
N
Br
N
CH3
4‐MeC
6
H ꢀ
4
N
CH3
N
CH3
2‐thienylꢀ
C
6
H
5
ꢀ
5mꢀ
N
N
S
Reactionꢀconditions:ꢀbenzilꢀ(1,ꢀ1ꢀmmol),ꢀaromaticꢀaldehydeꢀ2ꢀ(1ꢀmmol),ꢀprimaryꢀamineꢀ3ꢀ(1ꢀmmol),ꢀammoniumꢀacetateꢀ(4,ꢀ1ꢀmmol)ꢀandꢀ{Mo132}ꢀ(0.1ꢀg)
atꢀ140ꢀ°Cꢀunderꢀsolvent‐freeꢀconditions.ꢀ
aꢀ
AnꢀaqueousꢀsolutionꢀofꢀMeNH ꢀwasꢀusedꢀforꢀ5kꢀandꢀ5l.ꢀ
2
bꢀ
AllꢀofꢀtheꢀproductsꢀwereꢀcharacterizedꢀbyꢀIRꢀspectroscopyꢀandꢀaꢀcomparisonꢀofꢀtheirꢀmeltingꢀpointsꢀwithꢀthoseꢀofꢀtheꢀauthenticꢀsamples.ꢀTheꢀstruc‐
1
tureꢀofꢀsomeꢀofꢀtheꢀproductsꢀwereꢀalsoꢀconfirmedꢀbyꢀ HꢀNMRꢀspectroscopy.ꢀ

ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
1765ꢀ
Tableꢀ3ꢀ
Comparisonꢀofꢀtheꢀefficienciesꢀofꢀdifferentꢀcatalystsꢀforꢀtheꢀone‐potꢀfour‐componentꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazoles.ꢀ
Conditionsꢀ
Catalystꢀ
Timeꢀ(min)ꢀ
Yieldꢀ(%)ꢀ
Ref.ꢀ
Solventꢀ
MeOHꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
MeOHꢀ
—ꢀ
—ꢀ
T/°Cꢀ
refluxꢀ
140ꢀ
130ꢀ
140ꢀ
140ꢀ
130ꢀ
r.t.ꢀ
140ꢀ
140ꢀ
ꢀ 80ꢀ
refluxꢀ
120ꢀ
140ꢀ
Otherꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
—ꢀ
MWꢀ
—ꢀ
—ꢀ
—ꢀ
L‐Prolineꢀ
510–600ꢀ
120–150ꢀ
90–180ꢀ
120–150ꢀ
120ꢀ
60–120ꢀ
360–540ꢀ
120ꢀ
120ꢀ
3–4ꢀ
240ꢀ
120–240ꢀ
20–80ꢀ
76–88ꢀ
80–95ꢀ
80–91ꢀ
85–95ꢀ
80–93ꢀ
86–94ꢀ
49–84ꢀ
85–92ꢀ
82–91ꢀ
78–89ꢀ
73–86ꢀ
68–84ꢀ
86–97ꢀ
[24]ꢀ
[25]ꢀ
[26]ꢀ
[27]ꢀ
[28]ꢀ
[29]ꢀ
[30]ꢀ
[31]ꢀ
[32]ꢀ
[33]ꢀ
[34]ꢀ
[35]ꢀ
5
K CoW12
O
40.3H
2
Oꢀ
NH
Brönstedꢀacidicꢀionicꢀliquidꢀ
BF ‐SiO
Carbon‐basedꢀsolidꢀacidꢀ
InCl .3H Oꢀ
NaHSO /SiO
4 2
H PO
4
/Al
2
O
3
ꢀ
3
2
ꢀ
3
2
4
2
ꢀ
6 2 18
H P W O
62.24H
2
O/SiO
2
ꢀ
3
FeCl /montmorilloniteꢀK10ꢀ
—ꢀ
p‐Dodecylbenzenesulfonicꢀacidꢀ
MontmorilloniteꢀK10ꢀsupportedꢀtitaniumꢀ
2
H Oꢀ
—ꢀ
—ꢀ
{Mo132}ꢀ
thisꢀworkꢀ
ꢀ
catalyzedꢀtheꢀcondensationꢀreactionsꢀofꢀ1,ꢀ2,ꢀ3,ꢀandꢀ4ꢀtoꢀgiveꢀ
theꢀdesiredꢀproductsꢀ5a–5mꢀinꢀhighꢀyieldsꢀoverꢀrelativelyꢀshortꢀ
reactionꢀtime.ꢀItꢀisꢀnoteworthyꢀthatꢀtheꢀproductsꢀcouldꢀbeꢀread‐
ilyꢀseparatedꢀfromꢀtheꢀcatalyst,ꢀmakingꢀthisꢀmethodꢀespeciallyꢀ
tureꢀofꢀtheꢀcatalystꢀwasꢀunchangedꢀbyꢀtheꢀreaction.ꢀ
Aꢀplausibleꢀmechanismꢀforꢀtheꢀ{Mo132}‐catalyzedꢀformationꢀ
ofꢀtheꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀisꢀshownꢀinꢀSchemeꢀ2.ꢀ
Theꢀ {Mo132}ꢀ catalystꢀ hasꢀ severalꢀ accessibleꢀ Moꢀ sitesꢀ andꢀ NH ꢀ
4
usefulꢀforꢀtheꢀsynthesisꢀofꢀaꢀwideꢀrangeꢀofꢀ1,2,4,5‐
tutedꢀimidazoles.ꢀ
ꢀ
tetrasubsti‐
groups,ꢀwhichꢀcouldꢀactꢀasꢀLewisꢀacidꢀandꢀBrönstedꢀacidꢀcen‐
ters,ꢀrespectively,ꢀandꢀthereforeꢀpromoteꢀtheꢀreaction.ꢀTheꢀcat‐
Theꢀresultsꢀobtainedꢀinꢀtheꢀcurrentꢀstudyꢀusingꢀtheꢀ{Mo132}ꢀ
catalystꢀwereꢀcomparedꢀwithꢀthoseꢀpreviouslyꢀreportedꢀforꢀtheꢀ
synthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀusingꢀaꢀvarietyꢀ
ofꢀdifferentꢀcatalystsꢀ(Tableꢀ3).ꢀTheꢀresultsꢀofꢀthisꢀcomparisonꢀ
revealedꢀ thatꢀ theꢀ {Mo132}ꢀ catalystꢀ gaveꢀ shorterꢀ reactionꢀ timeꢀ
thanꢀ allꢀ ofꢀ theꢀ otherꢀ conditionsꢀ (exceptꢀ forꢀ theꢀ reactionꢀ cata‐
alystꢀwouldꢀplayꢀaꢀsignificantꢀroleꢀinꢀincreasingꢀtheꢀelectrophilicꢀ
characterꢀofꢀtheꢀelectrophilesꢀinꢀtheꢀreaction.ꢀAmmoniaꢀcouldꢀ
beꢀreleasedꢀfromꢀtheꢀammoniumꢀacetateꢀinꢀtheꢀreactionꢀwhichꢀ
couldꢀ beꢀ detectedꢀ usingꢀ aꢀ pHꢀ indicator.ꢀ Whenꢀ aꢀ pieceꢀ ofꢀ pHꢀ
paperꢀwasꢀheldꢀaboveꢀtheꢀreactionꢀmixture,ꢀaꢀblueꢀcolorationꢀ
wasꢀobserved.ꢀThisꢀresultꢀindicatedꢀthatꢀtheꢀreactionꢀproceededꢀ
byꢀtheꢀinitialꢀnucleophilicꢀattackꢀofꢀammoniaꢀandꢀtheꢀprimaryꢀ
amineꢀonꢀtheꢀcarbonylꢀgroupꢀofꢀtheꢀ{Mo132}‐activatedꢀaldehydeꢀ
withꢀconcomitantꢀdehydrationꢀtoꢀgiveꢀintermediateꢀI.ꢀInterme‐
diateꢀIꢀwouldꢀthenꢀreactꢀwithꢀ{Mo132}‐activatedꢀbenzilꢀtoꢀaffordꢀ
intermediateꢀII,ꢀwhichꢀwouldꢀbeꢀconvertedꢀtoꢀintermediateꢀIIIꢀ
throughꢀ aꢀ dehydrationꢀ reaction.ꢀ Finally,ꢀ theꢀ dehydrationꢀ ofꢀ
intermediateꢀ IIIꢀ wouldꢀ giveꢀ theꢀ 1,2,4,5‐tetrasubstitutedꢀ imid‐
azoleꢀproduct.ꢀAccordingꢀtoꢀthisꢀmechanism,ꢀtheꢀ{Mo132}ꢀcata‐
lystꢀwouldꢀfacilitateꢀtheꢀformationꢀofꢀintermediatesꢀI,ꢀII,ꢀandꢀIII.ꢀ
Severalꢀ attemptsꢀ wereꢀ madeꢀ toꢀ isolateꢀ theseꢀ intermediatesꢀ
underꢀ theꢀ optimizedꢀ conditions,ꢀ butꢀ allꢀ ofꢀ theseꢀ effortsꢀ wereꢀ
unsuccessful.ꢀ
lyzedꢀbyꢀFeCl /montmorilloniteꢀK10ꢀunderꢀmicrowaveꢀirradia‐
3
tion),ꢀasꢀwellꢀasꢀhigherꢀyieldsꢀofꢀtheꢀdesiredꢀproducts.ꢀ
Theꢀ reusabilityꢀ ofꢀ theꢀ catalystꢀ {Mo132}ꢀ wasꢀ alsoꢀ evaluatedꢀ
underꢀ theꢀ optimizedꢀ reactionꢀ conditions.ꢀ Uponꢀ completionꢀ ofꢀ
theꢀreaction,ꢀtheꢀcatalystꢀwasꢀrecoveredꢀaccordingꢀtoꢀtheꢀpro‐
cedureꢀ describedꢀ inꢀ theꢀ experimentalꢀ section.ꢀ Theꢀ recoveredꢀ
catalystꢀ wasꢀ washedꢀ withꢀ hotꢀ ethanolꢀ andꢀ thenꢀ driedꢀ underꢀ
vacuumꢀatꢀ50ꢀ°Cꢀforꢀ1ꢀhꢀbeforeꢀbeingꢀreusedꢀinꢀtheꢀsameꢀreac‐
tion.ꢀTheꢀresultsꢀofꢀthisꢀreusabilityꢀstudyꢀrevealedꢀthatꢀtheꢀcat‐
alystꢀcouldꢀbeꢀusedꢀatꢀleastꢀfourꢀtimesꢀwithꢀonlyꢀaꢀslightꢀreduc‐
tionꢀinꢀitsꢀactivityꢀ(Fig.ꢀ4).ꢀFurthermore,ꢀtheꢀFT‐IRꢀspectraꢀofꢀtheꢀ
recoveredꢀcatalystꢀ(Fig.ꢀ2(2)–(4))ꢀwereꢀalmostꢀidenticalꢀtoꢀthatꢀ
ofꢀtheꢀfreshꢀcatalystꢀ(Fig.ꢀ2(1)),ꢀwhichꢀindicatedꢀthatꢀtheꢀstruc‐
4.ꢀ ꢀ Conclusionsꢀ
97
100
95
94
93
Inꢀ conclusion,ꢀ weꢀ haveꢀ usedꢀ theꢀ Keplerate‐typeꢀ giantꢀ na‐
noporousꢀ isopolyoxomolybdateꢀ {Mo132}ꢀ asꢀ anꢀ efficientlyꢀ cata‐
lystꢀ forꢀ theꢀ synthesisꢀ ofꢀ 1,2,4,5‐tetrasubstitutedꢀ imidazolesꢀ inꢀ
theꢀ one‐pot,ꢀ four‐componentꢀ reactionꢀ ofꢀ benzilꢀ withꢀ anꢀ aro‐
maticꢀaldehyde,ꢀprimaryꢀamine,ꢀandꢀammoniumꢀacetateꢀunderꢀ
solvent‐freeꢀ conditions.ꢀ Thisꢀ methodꢀ providedꢀ theꢀ desiredꢀ
productsꢀ inꢀ highꢀ yieldsꢀ overꢀ shortꢀ reactionꢀ time,ꢀ followingꢀ aꢀ
facileꢀ work‐upꢀ process.ꢀ Furthermore,ꢀ theꢀ catalystꢀ couldꢀ beꢀ
readilyꢀ recycled,ꢀ andꢀ reusedꢀ atꢀ leastꢀ threeꢀ timesꢀ withoutꢀ anyꢀ
discernibleꢀreductionꢀinꢀitsꢀcatalyticꢀactivity.ꢀTheꢀprocedureꢀisꢀ
alsoꢀadvantageousꢀinꢀtheꢀsenseꢀthatꢀitꢀisꢀaꢀsolvent‐freeꢀreactionꢀ
andꢀthereforeꢀoperatesꢀunderꢀenvironmentallyꢀfriendlyꢀcondi‐
tions.ꢀ
8
6
4
2
0
0
0
0
0
1
2
3
4
Reaction cycle
Fig.ꢀ4.ꢀEffectꢀofꢀrecyclingꢀonꢀtheꢀcatalyticꢀperformanceꢀofꢀ{Mo132}ꢀinꢀtheꢀ
synthesisꢀofꢀ5b.ꢀ

1766ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
CH COONH4
3
4
{
Mo132
}
O
-
H O
H N
2
2
+
RNH2
+
NH3
Ar
Ar
H
RHN
2
3
(
I)
{Mo132}
{
Mo132
}
H
HO
Ph
Ph
HO
Ph
Ph
Ph
Ph
Ph
Ph
O
O
H N
N
N
N
N
N
2
H
-H O
H
-H O
2
2
+
Ar
Ar
Ar
Ar
RHN
N
HO
R
R
R
(I)
{Mo132
}
(II)
1
5a-5m
{Mo132}
(III)
Schemeꢀ2.ꢀPlausibleꢀmechanismꢀforꢀtheꢀ{Mo132}‐catalyzedꢀformationꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazoles.ꢀ
HirdꢀAꢀW,ꢀKingꢀFꢀD,ꢀLovellꢀPꢀJ,ꢀNaylorꢀA,ꢀReithꢀAꢀD,ꢀSteadmanꢀJꢀG,ꢀ
WilsonꢀDꢀM.ꢀBioorgꢀMedꢀChemꢀLett,ꢀ2006,ꢀ16:ꢀ378ꢀ
20] ChowdhuryꢀS,ꢀMohanꢀRꢀS,ꢀScottꢀJꢀL.ꢀTetrahedron,ꢀ2007,ꢀ63:ꢀ2363ꢀ
21] DavoodniaꢀA,ꢀKhojastehnezhadꢀA,ꢀBakavoliꢀM,ꢀTavakoli‐HoseiniꢀN.ꢀ
ChinꢀJꢀChem,ꢀ2011,ꢀ29:ꢀ978ꢀ
Acknowledgmentꢀ ꢀ
[
[
Theꢀ authorsꢀ expressꢀ theirꢀ gratitudeꢀ toꢀ theꢀ Islamicꢀ Azadꢀ
University,ꢀMashhadꢀBranchꢀforꢀitsꢀfinancialꢀsupport.ꢀ ꢀ
[22] DavoodniaꢀA,ꢀHeraviꢀMꢀM,ꢀRezaei‐DaghighꢀL,ꢀTavakoli‐HoseiniꢀN.ꢀ
MonatshꢀChem,ꢀ2009,ꢀ140:ꢀ1499ꢀ
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ꢀ
AhmadꢀNakhaeiꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ35ꢀ(2014)ꢀ1761–1767ꢀ
GraphicalꢀAbstractꢀ
1767ꢀ
Chin.ꢀJ.ꢀCatal.,ꢀ2014,ꢀ35:ꢀ1761–1767ꢀ ꢀ ꢀ doi:ꢀ10.1016/S1872‐2067(14)60174‐1
ApplicationꢀofꢀaꢀKeplerateꢀtypeꢀgiantꢀnanoporousꢀisopolyoxomolybdateꢀasꢀaꢀreusableꢀcatalystꢀforꢀtheꢀsynthesisꢀofꢀ
1,2,4,5‐tetrasubstitutedꢀimidazolesꢀ
ꢀ
AhmadꢀNakhaei,ꢀAbolghasemꢀDavoodnia*ꢀ
MashhadꢀBranch,ꢀIslamicꢀAzadꢀUniversity,ꢀIranꢀ
2.9 nm
ꢀ
{Mo132}ꢀefficientlyꢀcatalyzedꢀtheꢀsynthesisꢀofꢀ1,2,4,5‐tetrasubstitutedꢀimidazolesꢀunderꢀsolvent‐freeꢀconditions.ꢀTheꢀmethodꢀwasꢀrelativelyꢀ
fastꢀandꢀhighꢀyielding,ꢀandꢀtheꢀwork‐upꢀwasꢀeasy.ꢀTheꢀcatalystꢀusedꢀatꢀleastꢀfourꢀtimesꢀwithoutꢀanyꢀsubstantialꢀreductionꢀinꢀitsꢀcatalyticꢀ
activity.ꢀ
KajuꢀAꢀA.ꢀJꢀMolꢀCatalꢀA,ꢀ2006,ꢀ260:ꢀ77ꢀ
ChemꢀSoc,ꢀ2011,ꢀ32:ꢀ2243ꢀ
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N,ꢀKhojastehnezhadꢀA,ꢀZamaniꢀHꢀA.ꢀBullꢀKoreanꢀChemꢀSoc,ꢀ2011,ꢀ
1797ꢀ
32:ꢀ656ꢀ
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Zeinali‐DastmalbafꢀM.ꢀChinꢀJꢀChem,ꢀ2011,ꢀ29:ꢀ297ꢀ
1385ꢀ
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[45] DavoodniaꢀA,ꢀKhojastehnezhadꢀA,ꢀTavakoli‐HoseiniꢀN.ꢀBullꢀKoreanꢀ
1173ꢀ