第三講：反應(yīng)機(jī)理討論課件

反應(yīng)機(jī)理討論祝詩發(fā)第三講2009-11-03（ReactionMechanismDiscussion）delectronsingroup3arereadilyremovedviaionization,

thoseingroup11arestableandgenerallyformpartof

thecoreelectronconfiguration.valence(d)electroncount:過渡金屬原子的電子層結(jié)構(gòu)

過渡金屬由于其外層的d、s軌道能量相近，容易發(fā)生d/s躍遷，人們往往將d電子和s電子的總和稱為d電子數(shù)。游離過渡金屬:(n+1)sisbelow(n)din

energy(n=主量子數(shù)）零價(jià)過渡金屬絡(luò)合物:the(n)dlevelsarebelow

the(n+1)sandthusgetfilledfirst.group=delectroncount金屬離子絡(luò)合物subtracttheoxidationstatefromthegroup#.第一講內(nèi)容：過渡金屬基本概念TransitionMetalValenceOrbitalsTwoRules:9ValenceOrbitals:

upperlimitof9bondsmaybeformed.Inmost

casesamaximumof6σbondsareformedand

theremainingdorbitalsarenon-bonding.It'sthesenon-bondingdorbitalsthatgiveTMcomplexes

manyoftheiruniqueproperties.18electronrule:

upperlimitof18e-canbeaccomodatedw/out

usingantibondingmolecularorbitals(MO's).ElectronCountingligands:8e-metal:d8,8e-complex:16e-ligands:8e-metal:d10,10e-complex:18e-SetQuestions:

Calculatetheelectroncounts:

PdCl2,Pd(OAc)2

CommonGeometriesforTMComplexesσandπbondinginML6σ-π

電子授受配鍵FreeCOvibratesat2143cm-1.配體交換（配體的配位和解離）第二講內(nèi)容：基元反應(yīng)Associativeligand

substition

（締合）Dissociativeligandsubstitution（離解）Trans-Effect平面四方形配合物中某些配位體能使處于其反位的基團(tuán)變得更容易被取代，化學(xué)上稱這種能使反位基團(tuán)活化的現(xiàn)象為該配位體的反位效應(yīng)。反位于Cl-的基團(tuán)總是比反位于NH3的基團(tuán)更容易被取代，意味著Cl-的反位效應(yīng)比NH3大。順鉑具抗癌活性(干擾DNA復(fù)制)反鉑不具抗癌活性螯合效應(yīng)、大環(huán)效應(yīng)氧化加成與還原消除

(OxidativeAddition/ReductiveElimination)Notmechanism易發(fā)生OA的金屬絡(luò)合物：富電子、低價(jià)態(tài)、有空配位金屬；有強(qiáng)給電子配體

易發(fā)生OA的底物：極性底物Mingos

EssentialTrendsinInorganicChemistry;OxfordUniversityPress,1998.OA:Concerted3-centered(non-polarsubstrates)Hydrogenation(氫化)Dihydrogen

σ-complexesKubas

Acc.Chem.Res.1988(21)120.Dihydrogen

σ-complexesTaubeJACS1994(116)4352.Hydrogenation(氫化)Wilkinson’sCatalystInvestigationsintothereactivityof(PPh3)RhCluncovereditshighactivityasahomogeneoushydrogenationcatalyst.Thiswasthefirsthomogeneouscatalystthatcomparedin

rateswithheterogeneouscounterparts.Wilkinson'soriginalreportWilkinsonhydrogenation:classicdihydridemechanismThe‘HolyGrail’ofCatalysisC-HActivation代表催化劑設(shè)計(jì)的最高目標(biāo)C-HActivation:

sp3C-Hσcomplexregioselectivity:sp2C-H>1osp3C-H>2osp3C-H>>>3osp3C-H.sp3C-H:concertedvs.radicalAgosticinteractions:intramolecularσ-complex

（1997年：元結(jié)；2005年：抓氫鍵）Green,M.L.H.JOMC1983(250)395

Agostic：緣自古希臘荷馬史詩，由發(fā)現(xiàn)者英國教授Green提出中國石化張中岳：元結(jié)；譯者為了保持agostic身上所帶的古雅的文學(xué)內(nèi)涵，

擷取唐代大詩人李白和李商隱的名句中各一字組成“元結(jié)”

二字，并取意“原結(jié)”，“原來就存在的一種結(jié)合作用”，

以圖古樸典雅，又比較達(dá)意。

北大周公度：抓氫鍵；“抓住使靠在身旁”

AgosticinteractionsJ.Am.Chem.Soc.1974,96,754-760.Agosticinteractions：ApplicationC-CActivation:

sp3C-sp3Cσcomplexbonddissociationenergies(BDE)

BDE(C-H)>BDE(C-C):

C6H5-H:110kcal/mol

vs.C6H5-CH3:100kcal/mol

TMmediatedOA'sintoC-Cbondsare

muchmorerare

thanthoseforanalogousC-Hbonds.Formationoftheσ-complexis

kineticallydisfavored

by

stericrepulsion

betweenthemetalcomplexandthecarbonsubstituentsandbythehighdirectionalityofthesp3C-sp3Cbondthatlocalizestheσbondingorbitaldeepbetweenthecarbonnuclei.MilsteinJACS2000(122)9848.MilsteinOM1997(16)3981.OAwithCsp2-Xbonds:arylandvinylhalidesThreemainmechanismstoconsiderforthisprocess:Transmetalation(轉(zhuǎn)金屬)Definition:

Thetransferofanorganicgroupfromonemetalcentertoanother.

Theprocessinvolvesnoformalchangeinoxidationstate

for

eithermetal.Cross-CouplingReagentRX-couplingreactionLiR,MgXRvinyl,aryl,allyl,alkyl

KumadaRZrClCp2vinyl,alkylRZnClvinyl,aryl,alkyl

NegishiRCuLn

alkynyl,aryl

e.g.SonagashiraRSnR'3vinyl,aryl,alkynl

StilleRB(OR')2vinyl,aryl

SuzukiR-9BBNalkyl

Suzuki-MiyauraRSiR'3aryl,vinyl

HiyamaAlR2,AlX2alkyl

IngeneraltheratesoftransmetalationofRfollowtheorder:

alkynyl>aryl,vinyl>alkylTransmetalationMechanism：

theleast-studiedofthebasicreactionsteps.Inasimplepicture,themetalacceptingtheRgroupistheelectrophile

andtheM-Rbondbeingtransferredisthenucleophile.M-RbondformationmayormaynotbesimultaneouswithM’-Xbondformation,dependingon

thenatureofXandtheactualcomplexesinvolved.Withthismodel,increasingthenucleophilicityofRbyalteringtheligands

onM’andincreasingtheelectrophilicityofMthroughitsligandswill

facilitatethetransmetalationstep.Forweaklynucleophilic

transmetalationreagents,anadded

nucleophileorbaseoftenfacilitatesthetransmetalation.TransmetalationwiththeSuzukicoupling

oftenrequiresaddedbaseF-isthoughttoactivatetheorganosilicon

reagentfortransmetalation

viaformation

ofanucleophilic

pentavalentsilicatein

aHiyamacouplingReductiveElimination促進(jìn)還原消除的因素1)、吸電子烯烴；2)、CO（π酸）；3)、加熱；

4)、正電荷有利于還原消除；5）、BiteAngleEffects（咬角效應(yīng)）插入和反插入反應(yīng)（MigratoryInsertion/De-insertion）MechanismforCOinsertion:viaalkylmigrationtocoordinatedCOβ-HydrideEliminationWackerOxidationWackerOxidationReagentRX-couplingreactionLiR,MgXRvinyl,aryl,allyl,alkyl

KumadaRZrClCp2vinyl,alkylRZnClvinyl,aryl,alkyl

NegishiRCuLn

alkynyl,aryl

e.g.Sonagashir