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POM-based Chiral Hybrids Synthesis via Organoimidization Covalent Modification

of Achiral Precursors

Chapter 1

Advances in Chemical Engineering

Yifei Zhang 1,4†, Yichao Huang 2+, Huan Wang 1+, Jiangwei Zhang 1,2,3*, Gao Li1*, and Yongge

Wei2*

1State Key Laboratory of Catalysis & Gold Catalysis Research Center, Dalian Institute of Chemical

Physics, Chinese Academy of Sciences (CAS), Dalian 116023, PR China.2Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department

of Chemistry, Tsinghua University, Beijing 100084, PR China.3State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, Xiamen 361005,

PR China.4College of Chemistry and Chemical Engineering, Shenyang Normal University, Shenyang, 110034,

PR China.

† Equal Contribution

Correspondence to: Jiangwei Zhang, State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen

University, Xiamen 361005, PR China.

Email: [email protected]

Gao Li, State Key Laboratory of Catalysis & Gold Catalysis Research Center, Dalian Institute of Chemical

Physics, Chinese Academy of Sciences (CAS), Dalian 116023, PR China.


Yongge Wei, Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education,

Department of Chemistry, Tsinghua University, Beijing 100084, PR China


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In this chapter, covalent modification of POMs (polyoxometalates)clusters especially by organo imidization via the well-developed DCC(N,N′-dicyclohexylcarbodiimide)-dehydratingprotocolbyourgroupisbrieflyreviewed.ThefunctionalizationofPOMswithcovalentlyorganicmoietyisoneoftheeffec-tivewaystoincreasethediversePOMsfamilyandincorporateexceptionalproper-tiesthattheseorganicmoleculesattachtoPOMclustersinareliableandpredefinedmanner,whichisexpectedtobeappliedtothedesignofmolecularfunctionalizedmaterials.ThecombinationchiralitywithPOMsisacrucialbutchallengingissuesincePOMsusuallypossesshighsymmetry.Organoimidizationcovalentmodifi-cationofachiralprecursorsLindquist[Mo6O19]2−hasbeenprovedtobeaflexiblestrategyforapplyinginthegenerationofPOM-basedchiralhybrids.TheorganicligandsoffergreatopportunitiestoinstallstereogenicelementstoPOMsstructureasstructuredirecting-agentstoremovesymmetricelementsinPOMclusters,andsomespecialPOMclustersbearingaminogroupon itssurfaceservesasspecialimido ligands.This takes full advantage of the intrinsic hindrance of the bulkyandheavyPOMs,Whichwillgreatlyextendchiralityinpolyoxometalatechemis-trysincetheprimarychiralPOManionsarerare.InconsiderationofthefactthatthereexistplentyofchiralnaturalproductsL-aminoacidsandmanyPOMclustersanchoraminogroupasremotegrouponthesurface.ItcanforeseethatmoreandmorePOM-basedchiralhybridswillbegeneratedbyorganoimidizationcovalentmodificationofachiralprecursorsLindquist[Mo6O19]2−inthefuture.

Graphical abstract

1. Introduction Polyoxometalates (POMs) are an exceptional family of inorganic oxide anions con-sistingofearlytransitionmetalionssuchasMo,W,V,etc.attheirhighestoxidizationstatesbridgingbyoxideanionswithstructuralversatilityandawiderangeofpropertiesincludingcatalysis,medicineandmaterialsscience[1-3].SincethefirstsaltofPOM,ammonium12-molybdophosphate,(NH4)3[PMo12O40]wasreportedbyBerzelius in1826, thechemistryofPOMshasgaineddramaticdevelopment,withthedevelopmentofstructurecharacterizationtechnology,especiallysingleX-raydiffraction,thestructureofPOMsclustercanbeprecisely

Abstract


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confirmed.SinceKegginreportedthefamousKegginstructurein1934.Thetopologystruc-tureofKeggin[4],Anderson[5],Dawson[6],Waugh[7],Silverton[8],Lindqvist[9]werediscoveredsequentiallyandformedintothesixbasicstructureofPOMs.In1970s-1980s,sev-eralnovelstructuresincludingWeakley[10],Standberg[11],Finke[12],andPreyssler[13]werereported(Figure 1).POMs,asinorganicmultidentateligands,areprimecandidatesforthedesignandconstructionofdifferentdimensionalarchitectureswithjudiciousselectionofappropriatecationsandorganicmoleculesandPOMscanserveaselectroncontainersduetothepropertyofmulti-electronreductionwithoutlossofthearchitecture.TheseaspectsmakePOMsmorevaluablewithcharmingelectricalandopticalpropertiessuchaselectrochromism,photochromism,conductivity,andredoxactivitiesthatsuitableinawiderangeofpotentialapplication[14-21]suchasreversibleredoxactivitythatcanbeutilizedasefficientsolid-acidcatalystsandelectron-transfercatalystsfordiverseorganicreactions.

Figure 1: TenbasicstructuraltopologyofPOMclusters. Chiralityhasbecomeanincreasinglycrucialissueinmanyfields,rangingfromphar-maceuticalstoasymmetriccatalysisandclinicalanalysis[22-23].Thesynthesisandresolutionofchiralpolyoxometalates(POMs)isaninterestingbutchallengingareasincePOMsusuallypossesshighsymmetry.ChemistsareurgenttobreakthissymmetrysoastogetchiralPOMs.PreparationofPOMs’chiralstructureswouldprovideultimatecontrolofthesynthesisofthosenanosized objects.Generally speaking, chirality of POMs-based inorganic-organic hybrids

Figure 2: ClassicalintrinsicchiralPOMframeworks.


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canmanifest itself intwodistinctways[24-26]:(1)Theycanbeintrinsicallychiral intheframeworkofPOMsbybondlengthalteration,geometricaldistortion,theformationofstruc-turallacunaeandreplacementwithothermetals.ClassicalintrinsicchiralPOMframeworksare[MnMo9O32]

6−(Figure 2a),[PMo9O31(OH)3]3−(Figure 2b),α-[P2Mo18O62]

6−(Figure 2c),α1-[P2W17O61]

10− (Figure 2d)andβ2-[SiW11O39]8− (Figure 2e).However, suchenantiomers

areveryeasilyracemizedanddifficulttobeseparatedandisolated.Suchaproblemhasseri-ouslyhinderedtheapplicationofchiralPOM-basedmaterials.(2)POMsarechemicallymodi-fiedthroughcoordinationbonding,electrostaticinteractionandcovalentmodification.Sincemetalions,organiccationespeciallychiralorganiccationandsurfactants,organicligandscandramaticallyaffectthefinalarchitectures.SuchstrategymayleadtotherationaldesignandsynthesisofchiralPOM-basedmaterialsinenantiopureforms.

Organic–inorganicPOMshybridscanbecategorizedintotwoclassifications[20,27],classificationIandclassificationII (Figure 3),whicharewell-definedaccording to the in-teractionsbetweentheorganicand inorganicmoieties, tobeexact,non-covalentandcova-lentinteractions,respectively.ClassificationIorganic–inorganichybridscanbeassembledbyelectrostaticinteractions,hydrogenbonding,aswellas/orvanderWaalsinteractions.

Covalentmodification,bygraftingorganicmoietiesontoPOMsframework,namely,theorganicligandcansubstituteanoxogroupofthePOMandbedirectlylinkedtothemetalliccenter,resultingintheformationofclassificationIIhybrids.Thelaterhasgainedmuchatten-tionalthoughtheyarevastlydifferentinmolecularstructures,POMsandconjugatedorganicmoleculearebothelectricallyactivematerialswithsimilarelectricalandopticalpropertiessuchasphotochromism,electrochromism,andconductivity.Thefundamentalmechanismsofthesepropertiesare,however,differentforthesetwotypesofmaterials,withdπelectronsre-sponsiblefortheinorganicPOMclusters,anddelocalizedpπelectronsresponsiblefortheor-ganiccounterpart.Whilebothareashavebeenenjoyingconsiderablesuccess,therehasbeenonlyafewsuccessinbringingthesetwotypesofmaterialstogetherthroughcovalentbondstomakenovelPOM-basedorganic-inorganichybridsowingtothelacksofreliablestrategytofunctionalizePOMsandpreparetheirorganicderivativesinhighyield.Ascouldbeexpected,

Figure 3: Definitionofthetwoclassifications(IandII)oforganic/inorganichybridPOMs


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however,suchorganic-inorganichybridmaterialswillnotonlycombinetheadvantagesofor-ganicmaterials:suchasgoodprocessabilityandfine-regularstructureandelectronicproper-ties,withthoseofinorganicPOMclusters,suchasgoodchemicalstabilityandstrongelectronacceptability, to produce so-called ‘‘value-adding properties’’, but alsomay bring excitingsynergisticeffectsduetothecloseinteractionofdelocalizedorganicpπorbitswiththeinor-ganicPOMcluster’sdπorbits.

Comparedwithsuchorganic-inorganichybrids,POMsareconventionallypreparedbycoordination bonding or electrostatic interaction approaches,which lack predictability andcontrollability.However,theabilityofcovalentlymodifythePOMclustersinareliableandpredefinedmannerholdspromiseforthedevelopmentofmolecularmaterialsthatbridgethegapbetweenmolecularorganicandbulksemiconductingPOMscluster.Furthermore,givingexceptionalphysicalandstructuralpropertiesintrinsictoPOMsuperstructurescanbeachievedbypost-functionalizedthroughcommonorganicreactionsandapplyorganicallyfunctional-izedPOMclustersasbuildingblocks[28-29].

GraftingorganicmoietiesontoaPOMscluster requiresananchoragepointensuringthelinkbetweenthetwocomponents.ThislinkiscloselydependentonthechemicalstructurenatureandelectronicpropertiesofthePOMscluster.ThenucleophiliccharacteroftheoxygenatomslocalizedonthesurfaceofthePOMscanleadtocovalentinteractionswithelectrophilicgroupsbearingorganicgroups.ThepresenceofthenegativechargebornebythePOMsclusterisanimportantpointthatneedstobeconsideredforthegraftingoftheorganicmoieties.Neu-tralornegativelychargedorganicmoietieswillbechoseninordertofavorcovalentgraftingoverelectrostaticinteractions.ThefunctionalizationofPOMsthroughoxygenatomslocatedattheperipheryofthePOMstructureisthemostconventionalroute.OrganicligandwhichistheisoelectronicofO2-cansubstituteanoxogroupofthePOMandbedirectlylinkedtothemetalliccenter[30].

Basedon the coordinationmodes to covalently linkorganicmoietiesonto thePOMclustersurface.Thecommonlysyntheticstrategiescanbecategorizedintothefollowingmainclassifications: Organoimidization [28,31-34], Organoalkoxylation [35-48], Organotin [49-54],Organosilylation[55-63],Organophosphonylationandorganoarsonylation[64-72](Fig-ure 4).OrganicallyfunctionalizedPOMsapplyingspecificorganicligandsas linkersmakePOMs-basedinorganic-organicchiralhybridsmoreaccessibleandflexible.Inthisreview,wespeciallyfocusontheissuethatsuchPOMs-basedinorganic-organicchiralhybridswereob-tainedbythecovalentmodificationofachiralPOMclusterprecursorsapplyingorganicligandsasstructure-directingagentsbysymmetryreductionorbreakingtheachiralPOMcluster.


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2. Organoimidization by the DCC-dehydrating protocol

AmongtheabovementionedsyntheticstrategiesconcerningcovalentmodificationofPOMclusters,organoimidizationhasattractedparticularinterest.Strictlyspeaking,thedirectcovalentmodificationofthePOMclusterwithoutthebridgingthroughthetransitionmetaltheorganoimidizationof[Mo6O19]

2−istheonlysystem.Varioussyntheticapproachestoprepareorganoimidoderivativesof[Mo6O19]

2−usingdifferentorganoimido-releasingreagentshave-beensummarizedinapreviousbookchapterbyus[31].Recently,alotofarylimidoderiva-tivesincludingpolymersoftheLindqvisthexamolybdatecluster,[Mo6O19]

2-,havebeensyn-thesizedcontinuously[28].SincetheπelectronsintheorganiccomponentofsuchderivativesmayextendtheirconjugationtotheinorganicPOMframeworkviatheNatomsoftheimidogroups,thusresultinstrongd–pπinteractionsanddramaticallymodifytheelectronicstructureandredoxpropertiesofthecorrespondingparentPOMs.

Inaddition,organoimidoderivativesofPOMswitharemoteactivefunctionalgroupcanbeexploitedasbuildingblockstoconvenientlyandcontrollablyfabricatethecomplicatedcovalently-linkedPOM-basedorganic-inorganichybrids,includingthenano-dumbbells,poly-mericchainsandevennetworksofPOMs[28].Thismodularbuildingblockapproachbringsrationaldesignandstructureregulationintothesynthesisoforganic-inorganichybridmolecu-lar materials.

Inthisreview,wewilljustfocusonorganoimidizationof[Mo6O19]2−bytheDCC-de-

hydratingprotocolinbriefwhichhasalsobeenwellreviewedbyourgroup[28,34]anddem-onstratedhowthisprotocolcanbeappliedinchiralPOMshybridssynthesisthroughcova-lentmodification.Asitcanbeexpected,thereactionchemistryoforganoimidoderivativesofPOMsstandsforthefascinatingfutureofthechemistryoforganoimidoderivativesofPOMssinceitopensnotonlyanewroadtothechemicalmodificationofPOMs,butalsoanexcitingresearcharenawhereavarietyofhybridmaterialscontainingcovalentlybondedPOMclusters

Figure 4:CurrentexistedsyntheticstrategiesandmaincoordinationmodestocovalentlylinkorganicmoietiesontosurfaceofthePOMclusters.


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andorganicconjugatedsegmentscanbepreparedinmorecontrollableandrationalmanner.

Thehexamolybdateion,[Mo6O19]2-,isamongstthemostwell-knownPOMclustersfor

itsthermalandchemicalrobustandeasytobeprepared,whichhastheso-calledLindqviststructure. As it is depicted in Figure 5,theLindqviststructureconsistsofacentraloxyanionsurroundedinanoctahedralcageformedbysixmetalatoms.Allthesixmetalatomsalsohavean octahedral environment.

Besides thecentraloxygenatom, theyeachcoordinate triply tooneterminaloxygenatom,formingaterminalmetal-oxogroup(M≡O),andshareanadditionalfourdouble-bridg-ingoxygenatoms(μ2-Oatoms)withneighboringmetalatoms.Generallyspeaking,aLindqvistionhasasuper-octahedralstructureapproachtoOhpointgroupandfeaturesitssixterminalmetal-oxogroupsalignedalongtheCartesianaxes.Forthehexamolybdate,thesemolybdylgroups(Mo≡O)arereactiveenoughfortheterminaloxygenatomstobedirectlyreplacedbyvariousnitrogenousspecies.Theorganoimidoderivativesof [Mo6O19]

2−isgeneratedby thesubstitutionofoneormoreMo=Otermbond(s)byoneormoreMo≡NRbond(s).Monosubsti-tutedderivativescanbeobtainedwithavarietyoforganoimidoligandsusingthehexamolyb-dateanion[Mo6O19]

2−directlyorstartingfromtheoctamolybdateanion[Mo8O26]4-involving

thePOMreconstructionboth in thepresenceof theN,N′-dicyclohexylcarbodiimide(DCC)dehydratingagent.

2.1. Monosubstituted Derivatives

In the presenceof one equivalent ofDCC, one equivalent of primary amines reactssmoothlywithstoichiometric(n-Bu4N)2

[Mo6O19]underdryN2gasandrefluxingacetonitrile,to give the correspondingmono-substituted imidoderivatives usually in excellent yield ofmorethan90%.Notonlyavarietyofprimaryaminesoccurthisreaction,butalsoitisusuallycompletedinlessthan12hours,andpurecrystallineproductscanbereadilyobtainedwithconvenientbenchmanipulations.Moreover, thisreactioncanbecarriedout in theopenairwithoutnitrogenprotectionifslightlyoveroneequivalentofDCC(1.2equivalent)isadded.(Scheme 1)

[Mo6O19]2-+RNH2+DCC→ [Mo6O18(NR)]

2-+DCU

Scheme 1.TheMonosubstitutedorganoimidoderivatives[Mo6O18(NR)]2−synthesisby[Mo6O19]

2−directlyfunctional-

ization.

Moreover,inourrecentattemptstofunctionalizetheoctamolybdtateswithorganoimidogroups,wediscovered that in thepresenceofDCC, aproton coulddramatically speedupthereactionofα-[Mo8O26]

4-withprimaryaminesundermuchmildercondition.Meanwhile,monofunctionalizedorganoimidoderivativesof[Mo6O19]

2-wereselectivelysynthesizedinhighpurityandmoderateyieldwitheasyworkup.Thisacid-assistingroutehasallowedthefacile


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synthesisofalargenumberofmono-imidohexamolybdates.Itisworthpointingoutthat,theprotonwascrucialtotheaboveroutefortheformationofmonofunctionalizedderivatives.Itwasobservedthatintheabsenceofhydrochloridesalt–whichoffertheprotons,aminesreactedwithα-[Mo8O26]

4-toyieldonlythebifunctionalizedarylimidoderivativesofhexamolybdate.(see Scheme 2)

3CH CNrefluxing4 4 8 26 2. 4 2 6 18 43(N-Bu ) [Mo O ]+4RNH HC1+6DCC 4(Bu N) [Mo O (NR)]+6DCU+4Bu NC1→

Scheme 2.TheMonosubstitutedorganoimidoderivatives[Mo6O18(NR)]2−synthesisby[Mo8O26]

4- reconstruction.

2.2. Disubstituted Derivatives

Acharacteristic featureof thederivatizationof [Mo6O19]2− with organoimido ligands

isthecapacityforpolyfunctionalization.Amongorganoimidoderivativesof[Mo6O19]2−, the

bifunctionalizedonesaretheeasiestandmostcommonpotentialbuildingblocksforconstruct-ingPOM-basedhybrids.

3CH CNrefluxing2 4 4 8 26 4 2 6 17 2 4 2 2 72RNH +(N-Bu ) [Mo O ]+2DCC (Bu N) [Mo O (NR) ]+2DCU+(Bu N) [Mo O ]→

Scheme 3:Thedisubstitutedorganoimidoderivatives[Mo6O17(NR)2]2−synthesisby[Mo8O26]

4- reconstruction.

Inthepastyears,wealsocheckedthepossibilityofourDCC-dehydratingprotocolinthepreparationofdi-organoimidoderivativesofthehexamolybdate.Inmostcases,attemptstousethesamerouteasforthemono-substitutedderivativesbutwithastoichiometricratiooftwoequivalentaromaticprimaryaminesfailedtoobtainthedisubstitutedderivativesinhighyields.Instead,mixtureofvariouspolysubstitutedhexamolybdatesweregeneratedsincetherearesixequallyreactivesitesonahexamolybdateion,andthusrepeatedrecrystallizationisneededforpurificationoftheanticipantproduct.

However,anattempttofunctionalizetheα-isomerofoctamolybdateionα-[Mo8O26]4-,

withthisreactionroutineresultedintheselectivesynthesisofdifunctionalizedarylimidoderiv-ativesofhexamolybdatewithgoodyieldandhighpurity.Thereactionof(n-Bu4N)2 [α-Mo8O26]withDCCandorganoimidoligandsattheratioof1:2:2inrefluxingdryacetonitrilefor6to12hoursaffordedthecorrespondingdisubstitutedorganoimidoderivatives[Mo6O17(NR)2]

2−. Thisnovelrouteallowedtheefficientandselectivesynthesisofanumberofdi-organoimidohexamolybdateswithmoreconvenientandsimplebenchoperationsingoodyieldandhighpurity[73](Scheme 3).

Consideringexclusivelysterichindrance,thetransstructureofthedisubstitutedhexa-molybdate isexpected tobe theprincipalproductcomparedwith thecis isomer.However,thetrans-disubstitutedhexamolybdateshavehardlybeendetectedintheabovereactionroute.Sucharesultisamazing,whichsuggeststhatthestericeffectislessimportanthereandthe


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presenceofanexcessiveimidosubstituentinducesanactivatingeffectontheadjacentmo-lybdylgroups.ADFTstudyonhexamolybdatederivativesrevealsthatthecis-disubstitutedderivativesaremorestableinenergythanthecorrespondingtrans-isomers[74].

Scheme 4: Thedisubstitutedorganoimidoderivatives[Mo6O17(NR)2]2−synthesisby[Mo6O19]

2−directlyfunctionaliza-

tion.

We conducted our DCC-dehydrating protocol for the direct functionalization of[Mo6O19]

2−withstoichiometricratiosof(n-Bu4N)2[Mo6O19]andthecorrespondingorganoimi-doligands[75-76].Boththecis-andtrans-disubstitutedimidoderivativescouldbeobtainedinreasonableyields,respectively,bycarefulcontroloftherefluxingtime,reactiontemperatureandconcentration.Itshouldbenotedthatthecis-isomerisbyfarthemostcommonstructureamongthedisubstitutedspeciesevenifthekineticallycontrolledtransisomerhasbeenrecent-lyisolated[75-77].Ingeneral,prolongedrefluxingtimeathighconcentrationandhightem-peraturepromotestheformationofthecis-isomer,whilethetrans-isomercanbeisolatedfromarelativeshort-timeatlowconcentrationandlowtemperaturereactionsystem(seeScheme 4 and Figure 5).

Figure 5: Thecis-andtrans-disubstitutedmodeimidoderivativesof[Mo6O19]2−.


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Thiscompoundhasafeaturethattheμ2-bridgingoxygenatomsharingbythetwoimido-bearingMoatomsinacis-diimidohexamolybdateissubstitutedwithaμ2-bridgingorganoim-idoligand.Itsuggeststhatsuchoxygenatomsinthecis-diimidohexamolybdateshavebeendoublyactivatedbytheneighboringimidogroupsandbecomemorenegative(nucleophilic)thanotheroxygenatoms,resultingintheeasyelectrophilicattackbyDCC.ItstandsforthefirstexampleofabridgingoxygenatominPOMsreplacedbythebridgingimidogroups.Itbreaksthemyththatonlytheterminaloxogroupscanbedirectlyreplacedwithimidoligandsbefore and brings us awonderful prospect in the chemistry of organoimido derivatives ofPOMs(Figure 7).

2.4. Organoimido Derivatives of other POMs

Whiletherearefruitfuldevelopmentsinthesyntheticchemistryofhexamolybdate,re-latedstudiesonotherPOMskeepscarcelywelldeveloped.Sofar,thereonlyhasbeenobtainedquitelimitedsuccessinextendingtheaboveapproachestotheotherLindqvistPOMs.

Attempts todirectly functionalize thehexatungstateanion, [W6O19]2-, another impor-

tantLidquvisthomopolyoxometalatebesidesthehexamolybdate,havefailedtoutilizealltheexistingapproaches,since[W6O19]

2-doesnotreactatallwithphosphinimines,isocyanatesoraromaticprimaryaminesunderthepresentdevelopedconditions.Itseemsthatcomparedto

Figure 7: Ball-and-stickmodelofthetrisubstitutedhexamolybdate.

Figure 6: Twosubstitutionmodesofterminalorbridgingoxygenbyorganoimidoligands.

2.3. Polysubstituted Derivatives

WearealsointerestedinthepreparationofthepolysubstitutedhexamolybdatesinthecontextofourDCC-dehydratingprotocolusingprimaryaminesastheimido-releasingagents.Inarecentattempttosynthesizethefac-tri-2,6-dimethylanilidohexamolybdate,contrarytoourexpectation,theas-resultedtri-imidoderivative,(Bu4N)2[cis-Mo6O16μ2-(NAr)(NAr)2],wasnotexclusivelyterminal-oxoreplacedcomplex,andinstead,oneofbridging-oxogroupswassubstituted.Thisindicatedaveryimportantfactthatnotonlytheterminaloxogroupcanbesubstituted,butalsothebridgingoxogroupscanbereplacedbyaminegroups[78](Figure 6).


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themolybdylgroupsinthehexamolybdate,thetungstylgroupsinthehexatungstateisratherunreactive.Theonlyoneexampleofimidosubstitutedhexatungstates,(Bu4N)2[W6O18(NAr)],Ar=2,6-diisopropyl-C6H3,wasobtainedabouttwentyyearsagobyMaatta[79].

Althoughthehexatungstateclusterislesslabile,replacementoftungstylgroupswithreactivemolybdylgroupswillexertanactivateeffectonthecluster.Surely,wediscoveredthatthepentatungstenmolybdateion,[MoW5O19]

2-,aLidquvistheteropolyoxometalate,couldbedirectlyfunctionalizedwithprimaryaminesusingtheDCC-dehydratingprotocol[80].

[MoW5O19]2-+RNH2+DCC→ [W5O18(MoNR)]2-+DCU

Scheme 5.TheMonosubstitutedorganoimidoderivatives[W5O18(MoNR)]2-synthesisby[MoW5O19]2-directlyfunc-

tionalization.

In additionofone and ahalf equivalentsofDCC, the reactionofone equivalentof2,6-dimethylanilinewithoneequivalentof(Bu4N)2[MoW5O19]doesoccurinhotacetonitrileundernitrogen,affording themono-imidoderivatives (Bu4N)2 [W5O18(MoNR)]2-. Indeed as expected,theterminaloxygenatombondedtothemolybdenumatomwasselectivelyreplacedbyanimidosubstituent.ThisresultopensageneralroadforthesynthesisoforganoimidoderivativesoflessreactivePOMclusters,namely,byreplacementoneoftheinertterminalmetal-oxogroupswithafunctionalizableMo-Ogroup.

3. POM-Based Chiral Hybrids Synthesis via Organo imidization

The organo imidization strategy is applying in POM-based chiral hybrids synthesisthroughcovalentmodificationofachiralprecursorsPOMcluster[Mo6O19]

2−mainlyfocusesontheconstructionofchiralaxlespecies.Thedeterminationcriterionofwhetherorganic-in-organicPOMhybridshavechiralityornotdependsontheoverlappingwiththeirmirrorstruc-ture.Eventheredoesnotexistachiralcarboninorganic-inorganicPOMhybridsstructure,theycanstillbechiralifthereisachiralaxleinthestructure.Chiralitythatresultsfromchiralaxlecanbecataloguedintothreetypes:propadiene-type,biphenyl-typeandhandle-type.

For thebiphenyl-typechiralaxlecontainingPOM-basedchiralhybridsdesign.PengdesignedtwopairsofenantiopureC2-symmetric1,1’-binaphthylunitsbasedorganicligand.Throughthepost-functionalization,achiralprecursorsmonosubstitutedorganoimidoderiva-tives[Mo6O18(NR)]

2−covalentlylinkedtosuchchiralorganicligandandthechiralitytransferfromorganicligandtothewholePOM-basedhybrids[81].Suchhybridsshowedmoderatechiropticalbehaviourinsolution,andCottoneffectsareobservedupto450nm,indicatingchiralextensionfromthebinaphthylcoreofthecluster-containingπ-conjugatedarms(Figure 8).


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Intheviewofapplyingchiralorganicligandsasstructure-directingagentstotransferchirality to thewholePOM-basedhybrids strategy, chiral species are still consumed.Thisorganoimidization covalentmodificationwouldbemorevaluable if applying intrinsichin-dranceofthebulkyandheavyPOMs.Thenwefurtherpromotedthisstrategy.POM–organichybridchiralmolecularnanorodswereobtainedthroughorganoimidizationofachiralprecur-sorsLindquist[Mo6O19]

2−applyingachiralprecursorsAndersontypePOMsasspecialimidoligands.Theyalsodisplayedbiphenyl-typechiralaxleandC2-symmetryduetothehindranceofthebulkyandheavyPOMstotherotationaroundtheN–Csinglebond,whichstabilizedachiralconformation[82](Figure 9).

Figure 9: Thechiralnanorodssynthesisthroughorganoimidizationof[Mo6O19]2−applyingAndersontypePOMsas

special imido ligands.

Suchchiralnanorodswereobtainedinenantioenrichedformsbyspontaneousresolu-tion.TheirchiralitywasconfirmedbythesinglecrystalX-raydiffractionanalysesandsolidCDspectroscopymeasurements.AlthoughsuchC2-symmetricframeworksdonotpossessste-reogenicmetalions,thesyntheticstrategyprovidesanoriginalrouteforthedevelopmentofnovelchiralPOMarchitectures.WealsoextendedthisstrategytodesignanothertypeofchiralaxlePOM-basedchiralhybridssuchashandle-typePOM-basedchiralhybrids.

We applied anthranilic alkyl ether as imidization reagent,which ismoderately flex-ibleandnon-planeorganicmolecule.ByremovingsymmetricplaneandsymmetriccentersinPOMclustersandtheformationofring,wecouldobtainchiralmetalmacro-cycliccompounds[Mo6O17(C18H20N2O2)]2(±) through organoimidizationcovalentmodification by reacting

Figure 8 : The1,1’-binaphthylunitsbasedchiralorganicligandcovalentmodificationofachiralprecursorsmonosub-stitutedorganoimidoderivatives[Mo6O18(NR)]

2−.


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[Bu4N]4[α-Mo8O26],binaryaromaticamines(1,4-bis(o-amino-phenoxy)-butane,1,6-bis(o-amino-phenoxy)hexane,1,8-bis(o-amino-phenoxy)-octane),theirhydrochlorideandDCCinanhydrousacetonitrile[83]. Theflexiblealkylchainswhichconnecttwobenzeneringsinorganicligandcanresultinthecreationofchirality.SincethetwoendsoforganicligandarefixedontheMo6O18

2-byMo-Ntriplebond,theflexiblechaincannotbewigglefreely,sothatanasymmetricchainisformedandthesymmetryoftheoriginalMo6O19

2-canbebroken.Inthisway,thewholemetalmacro-cycleturnstobechiral.ThisisanimportantbreakthroughinPOMmetalmacro-cycliccompoundssynthesis(Figure 10). Taking theadvantageofdisubstitutedorganoimidizationstrategy,wealsoattempt todesignmultifunctionalhybridmaterialsbyintroducingaromaticandaliphaticorganicaminemoietiessimultaneously,indeedinsuchcis-disubstitutedimidoderivativesthesymmetrywasreduced to CipointgroupfromreactantsMo6O19

2-clusterwhichhashighsymmetryOh point group.Unfortunatelyspontaneousresolutionandchiralseparationofsuchdisubstitutedimidoderivativeshavenotyetachieved,however this indicated the important issue thatdisubsti-tuted/polysubstitutedorganoimidizationstrategyshouldalsobeaneffectivestrategyinchiralPOM-basedmultifunctionalhybridmaterialsdesign[84](Figure 11).

Figure 10:Chiralmetalmacro-cycliccompounds[Mo6O17(C18H20N2O2)]2(±)throughorganoimidizationcovalentmodi-ficationandtheirsolidCDspectroscopy.

Figure 11: Thesymmetryreductionbymixdisubstitutedorganoimidization.

Recently,wealsoattemptedtosynthesizetrisubstitutedimidoderivativesbyintroducingthebioactiveaminemolecule-amantadine,andthisisthefirstreportedtrisubstitutedderiva-tivesusingaliphaticorganoimidoligands.Similarly,suchfac-trisubstitutedimidoderivativesthesymmetrywasreducedtoD3dpointgroupwhichcouldserveasapotentialchiralsynthon[85](Figure 12).


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Figure 12: Thesymmetryreductionbytrisubstitutedorganoimidization

Considering the polyfunctionalization capacity character of the derivatizational[Mo6O19]

2−, this strategy designing through the post-functionalization monosubstituted or-ganoimido derivatives as building block becomes more accessible and flexible.We haveprovedthattheremainingterminalreactiveoxygenatomsinsuchorganoimidoderivativescanbefurtherfunctionalizedbyotherimidoligands[86].SincethefactthatthereexistplentyofchiralnaturalproductsL-aminoacidsandremoteaminogroupsonthesurfaceinPOMclus-tersincluding{[NH2C(CH2O)3]2V6O13}

2-[87],δ-{[NH2CC(CH2O)3]Cr(OH)3Mo6O18}3-[88],

{[C2H5C(CH2O)3]MMo6O18[(OCH2)3CNH2]}3- [89], χ-{[NH2CC(CH2O)3]Cr(OH)3Mo6O18}

3-

[90],{[NH2C(CH2O)3]2P2V3W15O59}6-[43],{Ni6O12[NH2C(CH2O)3](a-PW9O34)}[91].(Figure

13)

Figure 13: TheperspectiveofPOM-basedchiralhybridssynthesisbyorganoimidizationcovalentmodificationofachi-ralprecursorsLindquist[Mo6O19]

2−strategy.

4. Conclusion and Outlook

OrganoimidizationcovalentmodificationofachiralprecursorsLindquist[Mo6O19]2−is

aflexiblestrategyapplyinginthegenerationofPOM-basedchiralhybrids.ItpossessessterichindrancetoremovesymmetricelementsinPOMclusters,byintroducingspecificcustomizedorganicligands,whichincludeschiralorganicligandsasstructure-directingagentsorPOMclustersthatbearaminogrouponthePOMsurfaceandserveasspecialimidoligandstaking-fulladvantageofintrinsichindranceofthebulkyandheavyPOMs.ItcanforeseethatmoreandmorePOM-basedchiralhybridswillbegeneratedbyorganoimidizationcovalentmodifi-


15

cationinthefutureandsomerelatedinvestigationisbeingconductedinourlabnow

5. Acknowledgement

WethankthefinancialsupportbytheNationalNaturalScienceFoundationofChina(NSFCNo.21471087,21631007,21606220and21701168),thefundofthe“ThousandYouthTalents Plan”, LiaoningNatural Science Foundation (No. 20170540897) and open projectFoundationofStateKeyLaboratoryofPhysicalChemistryofSolidSurfaces,XiamenUniver-sity(No.201709).

6. References

1.M.T.PopeandA.Muller,Angew.Chem.Int.Ed.,1991,30,34.

2.A.MullerandP.Gouzerh,Chem.Soc.Rev.,2012,41,7431.

3.J.T.Rhule,C.L.HillandD.A.Judd,Chem.Rev.,1998,98,327.

4.J.F.Keggin,ProceedingsOftheRoyalSocietyOfLondonSeriesa-ContainingPapersOfaMathematicalAndPhysi-calCharacter,1934,144,0075.

5.J.S.Anderson,Nature,1937,140,850.

6.B.Dawson,ActaCrystallographica,1953,6,113.

7.G.BergmanandJ.L.T.Waugh,ActaCrystallographica,1953,6,93.

8.D.D.DexterandSilverto.Jv,J.Am.Chem.Soc.,1968,90,3589.

9.M.Che,M.FournierandJ.P.Launay,J.Chem.Phys.,1979,71,1954.

10.R.D.PeacockandT. J.R.Weakley, JournalOf theChemicalSociety a -InorganicPhysicalTheoretical, 1971,1836.

11.K.Y.Matsumoto,M.KatoandY.Sasaki,B.Chem.Soc.Jpn.,1976,49,106.

12.R.G.Finke,M.Droege,J.R.HutchinsonandO.Gansow,J.Am.Chem.Soc.,1981,103,1587.

13.Preyssle.C,BulletinDeLaSocieteChimiqueDeFrance,1970,30.

14.J.M.Clemente-Juan,E.CoronadoandA.Gaita-Arino,Chem.Soc.Rev.,2012,41,7464.

15.H.J.Lv,Y.V.Geletii,C.C.Zhao,J.W.Vickers,G.B.Zhu,Z.Luo,J.Song,T.Q.Lian,D.G.MusaevandC.L.Hill,Chem.Soc.Rev.,2012,41,7572.

16.M.NymanandP.C.Burns,Chem.Soc.Rev.,2012,41,7354.

17.X.Lopez,J.J.Carbo,C.BoandJ.M.Poblet,Chem.Soc.Rev.,2012,41,7537.

18.H.N.Miras,J.Yan,D.L.LongandL.Cronin,Chem.Soc.Rev.,2012,41,7403.

19.A.Proust,B.Matt,R.Villanneau,G.Guillemot,P.GouzerhandG.Izzet,Chem.Soc.Rev.,2012,41,7605.

20.Y.F.SongandR.Tsunashima,Chem.Soc.Rev.,2012,41,7384.


16

21.P.C.Yin,D.LiandT.B.Liu,Chem.Soc.Rev.,2012,41,7368.

22.J.He,S.H.Li,Y.Q.Deng,H.Y.Fu,B.N.Laforteza,J.E.Spangler,A.HomsandJ.Q.Yu,Science,2014,343,1216.

23.S.N.Mlynarski,C.H.SchusterandJ.P.Morken,Nature,2014,505,386.

24.B.Hasenknopf,K.Micoine,E.Lacote,S.Thorimbert,M.MalacriaandR.Thouvenot,Eur.J.Inorg.Chem.,2008,5001.

25.W.-L.Chen,H.-Q.TanandE.-B.Wang,J.Coord.Chem.,2012,65,1.

26.D.Y.Du,L.K.Yan,Z.M.Su,S.L.Li,Y.Q.LanandE.B.Wang,Coord.Chem.Rev.,2013,257,702.

27.A.Dolbecq,E.Dumas,C.R.MayerandP.Mialane,Chem.Rev.,2010,110,6009.

28.Z.H.Peng,Angew.Chem.Int.Ed.,2004,43,930.

29.D.L.Long,R.TsunashimaandL.Cronin,Angew.Chem.Int.Ed.,2010,49,1736.

30.A.Proust,R.ThouvenotandP.Gouzerh,Chem.Commun.,2008,1837.

31.Y.Wei,P.Wu,Y.WangandM.Shao,NovaSciencePublishers,Inc.,2007,pp.97.

32.Y.G.Wei,B.B.Xu,C.L.BarnesandZ.H.Peng,J.Am.Chem.Soc.,2001,123,4083.

33.Q.Li,Y.G.Wei,J.Hao,Y.L.ZhuandL.S.Wang,J.Am.Chem.Soc.,2007,129,5810.

34.J.Zhang,F.P.Xiao,J.HaoandY.G.Wei,Dalton.Trans.,2012,41,3599.

35.S.C.Liu,S.N.ShaikhandJ.Zubieta,Inorg.Chem.,1987,26,4303.

36.H.K.Kang,S.C.Liu,S.N.Shaikh,T.NicholsonandJ.Zubieta,Inorg.Chem.,1989,28,920.

37.D.Hou,G.S.Kim,K.S.HagenandC.L.Hill,Inorg.Chim.Acta,1993,211,127.

38.M.I.Khan,Q.ChenandJ.Zubieta,Chem.Commun.,1992,305.

39.P.C.Yin,P.F.Wu,Z.C.Xiao,D.Li,E.Bitterlich,J.Zhang,P.Cheng,D.V.Vezenov,T.B.LiuandY.G.Wei,An-gew.Chem.Int.Ed.,2011,50,2521.

40.D.Li,J.Song,P.C.Yin,S.Simotwo,A.J.Bassler,Y.Y.Aung,J.E.Roberts,K.I.Hardcastle,C.L.HillandT.B.Liu,J.Am.Chem.Soc.,2011,133,14010.

41.H.D.Zeng,G.R.NewkomeandC.L.Hill,Angew.Chem.Int.Ed.,2000,39,1772.

42.C.P.Pradeep,M.F.Misdrahi,F.Y.Li,J.Zhang,L.Xu,D.L.Long,T.B.LiuandL.Cronin,Angew.Chem.Int.Ed.,2009,48,8309.

43.C.P.Pradeep,D.L.Long,G.N.Newton,Y.F.SongandL.Cronin,Angew.Chem.Int.Ed.,2008,47,4388.

44.C.Allain,S.Favette,L.M.Chamoreau,J.Vaissermann,L.RuhlmannandB.Hasenknopf,Eur.J.Inorg.Chem.,2008,3433.

45.B.Hasenknopf,R.Delmont,P.HersonandP.Gouzerh,Eur.J.Inorg.Chem.,2002,1081.

46.P.F.Wu,P.C.Yin,J.Zhang,J.Hao,Z.C.XiaoandY.G.Wei,Chem.-Eur.J.,2011,17,12002.

47.J.W.Zhang,Y.C.Huang,J.Zhang,S.She,J.HaoandY.G.Wei,Dalton.Trans.,2014,43,2722.


17

48.C.Aronica,G.Chastanet,E.Zueva,S.A.Borshch,J.M.Clemente-JuanandD.Luneau,J.Am.Chem.Soc.,2008,130,2365.

49.S.Bareyt,S.Piligkos,B.Hasenknopf,P.Gouzerh,E.Lacote,S.ThorimbertandM.Malacria,J.Am.Chem.Soc.,2005,127,6788.

50.S.Bareyt,S.Piligkos,B.Hasenknopf,P.Gouzerh,E.Lacote,S.ThorimbertandM.Malacria,Angew.Chem.Int.Ed.,2003,42,3404.

51.I.Bar-Nahum,J.Ettedgui,L.Konstantinovski,V.KoganandR.Neumann,Inorg.Chem.,2007,46,5798.

52.K.Micoine,B.Hasenknopf,S.Thorimbert,E.LacoteandM.Malacria,Org.Lett.,2007,9,3981.

53.C.Boglio,K.Micoine,E.Derat,R.Thouvenot,B.Hasenknopf,S.Thorimbert,E.LacoteandM.Malacria,J.Am.Chem.Soc.,2008,130,4553.

54.K.Micoine,M.Malacria,E.Lacote,S.ThorimbertandB.Hasenknopf,Eur.J.Inorg.Chem.,2013,1737.

55.W.H.Knoth,J.Am.Chem.Soc.,1979,101,759.

56.P.Judeinstein,C.DeprunandL.Nadjo,J.Chem.Soc.Dalton.Trans.,1991,1991.

57.E.V.RadkovandR.H.Beer,Inorg.Chim.Acta,2000,297,191.

58.D.Agustin,C.Coelho,A.Mazeaud,P.Herson,A.ProustandR.Thouvenot,Z.Anorg.Allg.Chem.,2004,630,2049.

59.C.N.Kato,Y.Kasahara,K.Hayashi,A.Yamaguchi,T.HasegawaandK.Nomiya,Eur. J. Inorg.Chem.,2006,4834.

60.F.Bannani,R.ThouvenotandM.Debbabi,Eur.J.Inorg.Chem.,2007,4357.

61.T.Hasegawa,K.Shimizu,H.Seki,H.Murakami,S.Yoshida,K.YozaandK.Nomiya,Inorg.Chem.Commun.,2007,10,1140.

62.C.Cannizzo,C.R.Mayer,F.SecheresseandC.Larpent,Adv.Mater.,2005,17,2888.

63.D.Agustin,J.Dallery,C.Coelho,A.ProustandR.Thouvenot,J.Organomet.Chem.,2007,692,746.

64.W.Kwak,M.T.PopeandT.F.Scully,J.Am.Chem.Soc.,1975,97,5735.

65.J.K.StalickandC.O.Quicksall,Inorg.Chem.,1976,15,1577.

66.M.P.Lowe,J.C.Lockhart,G.A.Forsyth,W.CleggandK.A.Fraser,J.Chem.Soc.Dalton.Trans.,1995,145.

67.M.P.Lowe,J.C.Lockhart,W.CleggandK.A.Fraser,Angew.Chem.Int.Ed.,1994,33,451.

68.B.J.S.Johnson,R.C.Schroden,C.C.ZhuandA.Stein,Inorg.Chem.,2001,40,5972.

69.U.Kortz,M.G.Savelieff,F.Y.A.Ghali,L.M.Khalil,S.A.MaaloufandD.I.Sinno,Angew.Chem.Int.Ed.,2002,41,4070.

70.B.J.S.Johnson,R.C.Schroden,C.C.Zhu,V.G.YoungandA.Stein,Inorg.Chem.,2002,41,2213.

71.U.Kortz,J.Vaissermann,R.ThouvenotandP.Gouzerh,Inorg.Chem.,2003,42,1135.

72.U.Kortz,C.Marquer,R.ThouvenotandM.Nierlich,Inorg.Chem.,2003,42,1158.

73.L.Xu,M.Lu,B.B.Xu,Y.G.Wei,Z.H.PengandD.R.Powell,Angew.Chem.Int.Ed.,2002,41,4129.


18

74.L.K.Yan,G.C.Yang,W.Guan,Z.M.SuandR.S.Wang,J.Phys.Chem.B,2005,109,22332.

75.Y.Xia,Y.G.Wei,Y.WangandH.Y.Guo,Inorg.Chem.,2005,44,9823.

76.Y.Xia,P.F.Wu,Y.G.Wei,Y.WangandH.Y.Guo,CrystalGrowth&Design,2006,6,253.

77.J.W.Zhang,J.Hao,R.N.N.Khan,J.ZhangandY.G.Wei,Eur.J.Inorg.Chem.,2013,1664.

78.J.Hao,Y.Xia,L.S.Wang,L.Ruhlmann,Y.L.Zhu,Q.Li,P.C.Yin,Y.G.WeiandH.Y.Guo,Angew.Chem.Int.Ed.,2008,47,2626.

79.T.R.Mohs,G.P.A.Yap,A.L.RheingoldandE.A.Maatta,Inorg.Chem.,1995,34,9.

80.Y.G.Wei,M.Lu,C.F.C.Cheung,C.L.BarnesandZ.H.Peng,Inorg.Chem.,2001,40,5489.

81.M.Lu,J.H.Kang,D.G.WangandZ.H.Peng,Inorg.Chem.,2005,44,7711.

82.J.Zhang,J.Hao,Y.Wei,F.Xiao,P.YinandL.Wang,J.Am.Chem.Soc.,2010,132,14.

83.F.P.Xiao,J.Hao,J.Zhang,C.L.Lv,P.C.Yin,L.S.WangandY.G.Wei,J.Am.Chem.Soc.,2010,132,5956.

84.C.L.Lv,R.N.N.Khan,J.Zhang,J.J.Hu,J.HaoandY.G.Wei,Chem.-Eur.J.,2013,19,1174.

85.S.She,S.Bian,J.Hao,J.Zhang,J.ZhangandY.Wei,Chem.-Eur.J.,2014,20,16987.

86.J.Zhang,P.C.Yin,J.Hao,F.P.Xiao,L.Y.ChenandY.G.Wei,Chem.-Eur.J.,2012,18,13596.

87.A.Bayaguud,J.Zhang,R.N.N.Khan,J.HaoandY.Wei,Chem.Commun.,2014,50,13150.

88.J.W.Zhang,Z.L.Zhao,J.Zhang,S.She,Y.C.HuangandY.G.Wei,Dalton.Trans.,2014,43,17296.

89.J.Zhang,J.Luo,P.Wang,B.Ding,Y.Huang,Z.Zhao,J.ZhangandY.Wei,Inorg.Chem.,2015,54,2551.

90.J.W.Zhang,Z.H.Liu,Y.C.Huang,J.Zhang,J.HaoandY.G.Wei,Chem.Commun.,2015,51,9097.

91.S.T.Zheng,J.Zhang,X.X.Li,W.H.FangandG.Y.Yang,J.Am.Chem.Soc.,2010,132,15102.

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