第三講：反應(yīng)機理討論課件

反應(yīng)機理討論祝詩發(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變得更容易被取代，化學(xué)上稱這種能使反位基團活化的現(xiàn)象為該配位體的反位效應(yīng)。反位于Cl-的基團總是比反位于NH3的基團更容易被取代，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、低價態(tài)、有空配位金屬；有強給電子配體

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