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二氯乙烯锗烯与甲硫醛环加成的反应机理

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二氯乙烯锗烯与甲硫醛环加成的反应机理二氯乙烯锗烯与甲硫醛环加成的反应机理 二氯乙烯锗烯与甲硫醛环加成的反应机理 December 物理化学学报(WuliHuaxueXuebao) ActaPs.一Chim.Sin.,2008,24(12):2229—22352229 [Article] 二氯乙烯锗烯与甲硫醛环加成的反应机理 陈新11 (四川大学化学学院,成都610064; www.whxb.pku.edu.cn 李瑛, 皖西学院化生系,安徽六安237000) 摘要:利用MP2/6—311+G方法计算了单线态二氯乙烯锗烯与甲硫醛的...

二氯乙烯锗烯与甲硫醛环加成的反应机理
二氯乙烯锗烯与甲硫醛环加成的反应机理 二氯乙烯锗烯与甲硫醛环加成的反应机理 December 物理化学学报(WuliHuaxueXuebao) ActaPs.一Chim.Sin.,2008,24(12):2229—22352229 [Article] 二氯乙烯锗烯与甲硫醛环加成的反应机理 陈新11 (四川大学化学学院,成都610064; www.whxb.pku.edu.cn 李瑛, 皖西学院化生系,安徽六安237000) 摘要:利用MP2/6—311+G方法计算了单线态二氯乙烯锗烯与甲硫醛的各种反应机理.计算结果表明两者之间 的环加成反应具有很好的选择性,优势反应路径分为三步:首先两种反应物经过无能垒的放热反应形成中间体 INT,然后INT经历过渡态TS3异构化为P31,最后P31继续与甲硫醛反应形成二环杂环化合物P33.其中第一 步反应放热103.4kJ?mol一一,后两步反应能垒分别为0.7和32.3kJ?mol,. 关键词:二氯乙烯锗烯;硫醛;反应机理;选择性 中图分类号:0641 Cycl0additi0nReactionMechanismbetweenDichloromethylene GermyleneandMethanethial CHENXin.LIYing, (CollegeofChemistry,SichuanUniversity,Chengdu610064,P.R.China; 2DepartmentofChemistryandLifeSciences,WestAnhuiUniversity,Luan237000,AnhuiP rovince,PR.China) Abstract:TheoreticalcalculationsatMP2/6_31l+Glevelwereemployedtoinvestigatevario usreactionmechanisms betweensingletdichloromethylenegermyleneandmethanethia1.Calculationresultsindicatethatthedominantreaction pathwayforthisreactionconsistsofthreesteps.Thetworeactantsinitiallyformanintermedia tethroughabarrier- freeexothermicreactionof103.4kJ?mol,.ThisintermediatethenisomerizestoP31viaatransitionstateTS3withan energybarrierof0.7kJ?mol.P31finallyreactswithmethanethialtoformthegermanicheteropolycyclicproductP33 withanenergybarrierof32.3kJ?mol.Thiscycloadditionreactionthushasexcellentselectivit y. KeyWords:Dichloromethylenegermylene;Methanethial;Reactionmechanism;Selectivity Recently,muchaRentionhasbeendirectedtowardgermylenes frombothexperimenta1andtheoreticalaspects[1-131.Generally. germyleneisakindofquiteunstableactiveintermediate. Germylenereactionshaveattractedconsiderableattentionasan effectivemethodinthesynthesesofnewbondsandheterocyclic compoundswithGe【,1.Forexample.oneofthebest—studied germylcries,:GeCI2~.reactswithalkenesbyanunknownmech- anismtogiveavarietyoforganogermaniumproducts,including allalkene-germylenecopolymer~.Thesamephenomenoncanalso befoundintheadditionreactionofgermylenest0ace?Jenic derivatives.whichusually1cadstoeitherdimersorpolymerst. Onthecontrary,thethree—membered—ringcyclopropaneandcy- clopropenearetheprimaryproductsoftheearbeneadditionre— actionswitholefinsandacetylenes.respectively【,.Unfortu- nately,themechanisticbasisofgermylenechemistryisstill poorlyunderstood,anditmakesmanygermylenereactionsun- reliableforsyntheticplanning.Moreover,noestimatesoftheab— soluteactivationenergiesofsuchadditionsareasyetavailable fromexperiments.Thecalculationsofreactionpathwaysfor germylenecycloadditionsandthelocationandidentificationof thestructuresofthetransitionstatesisthereforeofgreattheoret- icalinterest. Asheaviercarbeneanalogues,germylenescallbeclassified intotwotypes,i.e.thesaturatedandtheunsaturated,justlike carbenes.Fromprevioustheoreticalstudyresults,itseemspossi- bletoconcludethatthereactionsbetweensaturatedgermylenes Received:June19,2008;Revised:September23,2008;PublishedonWeb:October20,2008. Correspondingauthor.Email:qingjiang2002@163.corn;Tel:+8628—85418330. 教育部重点项目(105142)和四川省青年科技基金(03SQO4)资助 ?EditorialofficeofActaPhysico—ChimicaSinica 2230ActaPs.一Chim.Sin..2008Vo1.24 (:GeX2,X=H,F,C1,Br)andalkenesundergotheweaklybound germylene/alkenecomplexprecursors,andthatthe7『一complex mightbeobservableingasphasegermylene/alkenereaction mixturesatlowtemperature?.Thisphenomenonofgermylene additionsisdifferentfromthatinthecorrespondingcarbenead. ditions,inwhichstablecarbene/alkenecomplexes,inparticular complexesbetween:CC12andethyleneandtetramethylethylene, donotexistt22]. Therehavebeenmanytheoreticalstudiesonthereaction mechanismsbetweenunsaturatedcarbenesandalkenesaldehy— des,andketones,andthecommonfirstreactionstepisthefor— marionofthe仃一complexprecursorsbetweenthereatants[23,24]. whichissomewhatdifierentfromthoseofthecorresponding saturatedcarbenes[.Onthecontrary.studiesOilthereaction mechanismsofunsaturatedgermylenes(:Ge--CX2)arereally sparse[25-2.Uptodate,itisnotwellknownwhetherthedifference ofreactionmechanismsbetweensaturatedcarbenesandunsatu. ratedcarbenesarestilltrueforgermylenes.Futhermore.elec— tronic..donatingand/orelectronic..drawingconditionsofsub.. stituentXmayaffectcycloadditionreactivityof:GeCX2,theo— reticalstudyonthisaspectwouldbehelpfulforpracticalsyn— theticplanning.Hence,theresearchongermylenesandgermy— lenereactionshasimportanttheoreticalandpracticalsignifi— cances. Onthebasisofaboveconsiderations,theoreticalstudyonthe eyeloadditionreactionmechanismsbetweenunsaturateddichloro— methylenegermylenesandmethanethialwascarriedout.Inthis paper,reactionmechanismbetweenthemwasinvestigatedand analyzedintermsofthreepossiblepathwaysofcycloaddition reaction.A】lthejnvolvedreactionchannelsareasfollows: Pach…2C=Ge:+H2C= c e SR1R2n2'一 Path2Cl2C=Ge:+H2C—S R1R2 CI2 P21 P22 P23 P24 P31 2 P32 P33 1Calculationmethods B3LYP/6—3l+GandMP2/6—311+Gimplementedinthe Gaussian98口目packagewereemployedtolocateallthestationary pointsalongthereactionpathways,respectively.Fulloptimiza— tionsandfrequencyanalysesweredoneforthestationarypoints onthereactionprofile.Toexplicitlyestablishtherelevant species,theintrinsicreactioncoordinate(IRC)wasalsocalculated forallthetransitionstatesappearingonthecycloadditionenergy surfaceprofile.Relativeenergieswereobtainedthroughthree methods,namelyB3LYP/6—31+G//B3LYP/6—31+G,MP2/6— 311,//B3LYP/6—31+G,andMP2/6—31l+G//MP2/6-311+G, respectively.BecausetheMP2theoryisparticularlyimportant forreliableenergypredictionforsystemscontaining7r_+仃in- teraction[29-35].andthe6—311+Gbasissethasbeenproventobe reliableindescribingsimilarsystemsasdescribedinRef.『36— 38],unlessotherwisenoted,therelativeenergiesreportedinthe textcorrespondtotheMP2/6—311+G*//MP2/6—31l+leve1.in— cludingthezero—pointenergycorrection.Ascalingfactorof 0.9804[wasusedtocorrectthedirectlycomputedzero—point energies(ZPEs).A1lcalculationswereperformedwiththeGaUS sian98suiteofprograms. 2Resultsanddiscussion 2.1Path1 Thegroundstateenergyofdichloromethylenegermylenein singletis108.75kJ'mollowerthanthatoftripletstateaccord— ingtocalculationresults,whichmeansthatthesteadyground stateofdichloromethylenegermyleneisasingletstate.Asillus— tratedabove,Path1betweendichloromethylenegermylene(R1) andmethanethial(R2)formsathree—memberedringproduct(P1). Thisreactionconsistsoftwosteps.Thefirstoneisabarrier—free exothermicreactionof一103.4kJ'mol,,givinganintermediate (INT).Then1NTisomerizestoP1withabarrierof33.5kJ?mol.., viatransitionstate(TS1).Themajorgeometricalparametersof reactants(R1andR2),intermediateaNT),transitionstate(TS1), product(P1)aregiveninFig.1,andthepotentialenergysurfaces aregiveninFig.2.TheenergiesarelistedinTable1.Theunique imaginaryfrequencyofthetransitionstateTS1isapproximately ,and1RCcalculationofTSIandfurtheroptimization 600icm, fortheprimaryIRCresultsconfirmitconnectsINTandP1. Theadditionofasingletgermylenetomethanethialinvolves simultaneousinteractionsofthevacantgermylenicPorbital (LUMO)withthefilledmethanethia17rorbita1fH0M01andof thefilledgermylenico-orbitalfHOM01withthevacantmethanethia1 77"orbital(LUMO).Althoughasingletgermyleneisinherently bothanelectrophileandanucleophile.itsbehaviorhereisdeter. minedbytheelectrondistributioninthetransitionstate.Thisde— pendsonwhethertheLUMHOM0orHOMO LUM0m甜?劬interactionisstrongerinthisstate.Moreover,ac— cordingtoHoffmannsworkt.therearetwopossibleroutesfor additionofagermylenetomethanethialasshowninFig.1(a,b). The7rapproachinFig.1(a)(nonleastmotion),withthePorbital ofthegermyleneimpingingonthe7rsystemofmethanethial, No.12CHENXineta1.:CycloadditionReactionMechanismbetweenDichloromethyleneG ermyleneandMethanethial2231 lI{2 S NT b rSlP Fig.1OptimizedstructuresofinvolvedspeciesofPath1atMP2/6?311+Glevel bondlengthinnlllandbondangleindegree;a:7rapproach.b:r,approach hasonlyoneplaneofsymmetry,makingthisreactionsymmetry allowed.Ontheotherhand,Fig.1(b)givesthemostsymmetrical transitionstateandhasbeencalledtheo-approach(1eastmo— tion),becausetheo-orbitalofthegermyleneimpingesonthe methanethial仃system.Hoffmann【40]haspointedoutthattheo- approachinFig.1(b)is"forbidden"intermsoftheconservation oforbitalsymmetryandisthereforeexpectedtobehighinener- gY.Onthisbasis,thepreferredapproachshouldbethe7rap? proachinFig.1(a),inwhichthefilled仃MOinteractswiththe emp够Porbitalofthegermylene. AtthebeginningofPath1,thevacant4porbitalofelec— tropositiveGeatominsertsintothe7rorbitalofCSbondfrom theendofelectronegativeSatom,andasemi—cyclicintermedi— atecomplexformsalongwith7relectronmigratingintotheva— cant4porbitalsofGeatom.Becausethereisstrongbond—form- ingtendencybetweeno-lone-pairelectronofgermyleneandanti— bond仃orbita1ofC1endofmethanethia1.theo-一77-typedona— O 一 50 一 100 _. i—I50 王 - 200 司 一 250 - 300 Rl+R2P2l+R2 P3 4 3 Fig.2Thepotentialenergysurfaceforthecycloaddition reactionsbetweendichloromethylenegermyleneand methauethialatMP2/6.311+GIIMP2/6.311+Glevel S tor-acceptorC1—Gebondcontinuouslystrengthens.untilulti. matelythesingletC1.叫Gebondforms.Duringtheformation courseofC1-_Gebond.germylenerotatesanticlockwisewhile methanethialrotatesaroundC1一Sbondtoensureo-1one—pair electronsofGeatomcontactfullvwim77"orbitalofmethanethia1. Aboveanalysesrevea1thatPathlisaconcertedandasyn. chronous+11additionreaction,justlikethereactionofthesin— gletgermyleneadditiontoethylene. BothRlandR2areplanarandinCsymmetry.butwhenthey formreactantcomplex【NT.theirstructuresgeneratedramatical deformation.Uponformationof1NT,bondlengthofC=Sin R1increasesfrom0.1614toO.17l1amandC=GeinR2in— creasesfrom0.1858to0.1937nm.Atthesametime.bond lengthoftwoC—HbondsinR1andtwoC—C1bondsinR2are nolongerequivalent,theydecreasetodifferentextentcompared tothoseofR1andR2.Itisworthnoting廿1atfouratomsofR1 andfouratomsofR2arenotatthesameplaneonformationof INT.fordihedralangleofHlClSH2andC11C2GeC12are l58.1.and178.7.respectively. UponformationofP1fromINT,viaTS1,contrarytothe graduallydecreasetendencyofbondlengthofC2--Ge,C1—Ge, andGe--S.bondlengthofC1一Sgraduallyincreasefrom 0.171lto0.1885am.andultimatelyformatypicalsinglebond. Duringthiscourse,doublebondC2Ge,singlebondsCl—Ge andGe---Salsofo1-in.P1ismoresimilartoTS1thanINTbv structure.itisalsoconfirmedbydihedralangleofC2GeSC1 (INT:-85.4.,TS1:一103.6.,P1:-1l1-3.),C12C2GeS(INT: 5.5.,TS1:一30.8.,PI:一60.7.),CI1C2GeS(INT:一173.2.,TSI: 174.0..P1:150.3.1. AsseeninFig.2,theenergydifferencebetweenTS1andP1 isonly10.7kJ?mol,.itindicatesthatP1caneasilyconvertto INTviaTS1.ThesecondstepofPath1isreversible.anditmay 哦一 2232ActaPhys.-Chim.Sin.,2008V01.24 Table1Relativeenergiesforthespeciesobtainedwith differenttheoretica/methods Species kJmol?f?1 abc Rl+R200000.0 INT一856—1016—1034 TS1-764-71.7-699 P1-77.5-80.3-80.6 TS2-78.5-84.8-89.7 P21-1680-2024-2022 TS22-151.8-1762-1760 P22-239.5-242.9-2425 TS23-12.1—25.7一l7.6 P23—46.2-596-605 TS3-81.4-1016-1027 P3l-279.9-2964-2973 TS32-2174—188.8-192.6 P32—247.9-2576—260.2 P2l+R20.0000.0 INT24-423-38l-416 TS24-184-15.2-149 P24-137.1-1410-1415 P:{l+R2-112l-q40-95l INT33-1557-1536-155.7 TS33-103.7-123.7—123.4 P33-205.3-209.8-2084 a:B3LYP/6-31+G//B3LYP/6—31+G.b:MP2/6—3ll++G"//B3LYP/6—31+G. c:MP2佑.3ll+G//MP2/6-31l+G beduetotheunstablestructureofP1. 2.2Path2 InPath2,therearethreepossiblepathways,allofthethree differentwayshavethecommonfirststep,whichistheforma— tionofP21.P2lthenisomerizestoP22aridP23.orreactswith R2afterwardsandfotinsP24. Therearetwopossiblewaysfortheformationof[2+2】cy— cloadditionproductP21betweensingletdichloromethylene germyleneandmethanethia1.Oneisthedirectformationthrough 【2+2]cycloadditionreaction,andtheotheristhatreactantscom- bineinto[2+1]qr—complexprecursorfirstly,andthenisomize into[2+2】cycloadditionproduct.Fromthepointofviewofther- modynamicsanddynamics,thelatterismorefavourablethan theformer.Furthermore.thedirectformationoffour.membered— ring[2+2]cycloadditionproductisthermalforbiddenaccording toWoodward—Hoffmannmle. AsshowninFig.3,upontheformationofP21,R1andR2 firstlyformlNTjustthesameasPath1,thenINTisomerizesto P21,viaTS2.Wilhthereactiongoingon,thedihedralangles C2SC1Ge(INT:一43.0.,TS2:一44.1.,P21:一48.6.)graduallyin— creaseandtheGeC2SC1(INT:80.6.,TS2:61.0.,P21:48.3.)grad— uallydecreases,andthe1NTfinallytransformsintothetwisted four—membered-ringproductP2lviathetransitionstateTS2.At thesametime,bondangleofGeC2S(INT:50.8.,TS2:60.3., P21:78.1.)andSC1Ge0NT:73.1.,TS2:76.1.,P21:78.8.)gradu— allyincrease.Amongthefoursinglebondsofthetwistedfour— memberedring.bondlengthofC2一Schangemostdramatically (INT:0.3lI,TS2:O.272,P2l:0.184)whiletheotherschange onlyabout0.01-0.02nm.Activationbarrierofthisreactionis 13.7kJ?mol,. Forthefirstpathway,P22isformedthroughtheisomerization ofP21v/aTS22,achlorideatomffansformsfromC2atomto germaniumatomandC=Geformssimultaniously,activation barrierofthisreactionis26.2kJ'mol,.Forthesecondpathway, P23isformedthroughtheisomerizationofP21viaTS23,ahy— drogenatomtransformsfromC1atomtogermaniumatomand CGeformssimultaniously,activationbarrierofthisreactionis 184.6kJ?mol,.Becauseofhighactivationbarrierforformation ofP23,itisquitedifficulttoobtainhydrogentransferproduct P23atroomtemperature.QuiteshortseparationbetweenHand C1(0.1088and0.1092nm,respectively)andlongseparationbe— tweenC1andGe(O.2037am)inP21makeitquitedifficultfor HtotransferfromC1toGe.StepDandstepEinFig.2and Table2competewitheachotherwithanenergybarrierdiffer- enceof158.4kJ?mol一.andthelatterismucheasiertotake placethantheformer.Inotherwords,C1transferismucheasier thanHtransferforthebetweendichloromethylenegermyleneand methanethial,asisthesameasthereactionbetweendichloromethy? lenegermyleneandethylene~.TheenergybarriersofstepsBand Eforthereactionbetweendichloromethylenegermyleneand methanethia1are13.7and26.2kJ?mol.respectively(asseenin Table2),whiletheenergybarriersofcorrespondingstepsforthe reactionbetweendichloromethylenegermyleneandethyleneare 57.7kJ?moland42.2kJ?molratCCSD(T)//B3LYP/6—3I+G leve1)t2,respectively.Thereactionbetweendichloromethylene germyleneandmethanethialismucheasiertotakeplacethanthe reactionbetweendichloromethylenegermyleneandethylene. BothP22andP23arefarfromplanarstructure,fordihedralan- glesofC1GeC2S(P22:21.86.,P23:-13.29.),H1C1GeH2(P23:一 61.43.)andCl1C2GeCl2(P22:-69.35.)deviatefrom0.or 180.. Sincethesploneelectronpairandthe和unoccupiedorbital onGeatomdonotparticipateinbondformation,P21isstillan activeintermediate.ItisnotdifficulttopredictthatP21canfur- therreactwithmethanethialtoformapolycycliccompound.As showninFig.2,thethirdwayconsistsoftwosteps,abarrier—free exothermicreactionof41.6kJ?molresultsinanintermediate INT24,then1NT24isomerizingtoP24withabarrierof26.7kJ' mol,. Thegeometricparametersforthetransitionstates(TS2,TS22, TS23,andTS24),intermediate(INT24),andproducts(P21,P22, P23,andP24)appearinginPath2betweensingletdichloromethy- lenegermyleneandmethanethialaregiveninFig.3.Theener- giesarelistedinTable1.ThepotentialenergysurfaceforPath2 isillustratedinFig.2. TheuniqueimaginaryfrequenciesofthetransitionstatesTS2, TS22,TS23,andTS24are644.7i,416.2j,771.5i,and984.7i cm,,respectively,andthereforethetransitionstatescanbeaf- firmedastherealones.Accor?
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