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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