第三讲：反应机理讨论课件

反应机理讨论反应机理讨论祝 诗 发第三讲第三讲2009-11-03（Reaction Mechanism Discussion）d electrons in group 3 are readily removed via ionization,those in group 11 are stable and generally form part of the core electron configuration.valence(d)electron count:过渡金属原子的电子层结构过渡金属原子的电子层结构过渡金属由于其外层的过渡金属由于其外层的d d、s s轨道能量相近，容轨道能量相近，容易发生易发生d/sd/s跃迁，人们往往将跃迁，人们往往将d d电子和电子和s s电子的电子的总和称为总和称为d d电子数。电子数。游离游离过渡金渡金属属:(n+1)s is below(n)d in energy(n=主量子主量子数数）零价零价过渡金渡金属属络合物合物:the(n)d levels are below the(n+1)s and thus getfilled first.group=d electron count金金属属离子离子络合物合物subtract the oxidationstate from the group#.第一讲内容：过渡金属基本概念第一讲内容：过渡金属基本概念Transition Metal Valence OrbitalsTwo Rules:9 Valence Orbitals:upper limit of 9 bonds may be formed.In most cases a maximum of 6 bonds are formed and the remaining d orbitals are non-bonding.Its these non-bonding d orbitals that give TM complexes many of their unique properties.18 electron rule:upper limit of 18 e-can be accomodated w/out using antibonding molecular orbitals(MOs).Electron Countingligands:8 e-metal:d8,8 e-complex:16 e-ligands:8 e-metal:d10,10 e-complex:18 e-Set Questions:Calculate the electron counts:PdCl2,Pd(OAc)2 Common Geometries for TM Complexes and bonding in ML6-电子授受配键电子授受配键Free CO vibrates at 2143 cm-1.配体交换（配体的配位和解离）配体交换（配体的配位和解离）第二讲内容：基元反应第二讲内容：基元反应Associative ligand substition（缔合）合）Dissociative ligand substitution （离解）（离解）Trans-Effect平面四方形配合物中某些配位体能使处于其反位的基团变得更容易被平面四方形配合物中某些配位体能使处于其反位的基团变得更容易被取代，化学上称这种能使反位基团活化的现象为该配位体的取代，化学上称这种能使反位基团活化的现象为该配位体的反位效应反位效应。反位于反位于Cl-的基团总是比反位于的基团总是比反位于NH3的基团更容易被取代，意味着的基团更容易被取代，意味着Cl-的反位效应比的反位效应比NH3大。大。顺铂顺铂具抗癌活性具抗癌活性(干扰干扰DNADNA复制复制)反铂反铂不具抗癌活性不具抗癌活性螯合效应、大环效应螯合效应、大环效应氧化加成与还原消除氧化加成与还原消除(Oxidative Addition/Reductive Elimination)Not mechanism易发生易发生OA的金属络合物的金属络合物：富电子、低价态、有空配位金属；有强给电子配体富电子、低价态、有空配位金属；有强给电子配体易发生易发生OA的底物：的底物：极性底物极性底物Mingos Essential Trends in Inorganic Chemistry;Oxford University Press,1998.OA:Concerted 3-centered(non-polar substrates)Hydrogenation(氢化化)Dihydrogen-complexesKubas Acc.Chem.Res.1988(21)120.Dihydrogen-complexesTaube JACS 1994(116)4352.Hydrogenation(氢化氢化)Wilkinsons CatalystInvestigations into the reactivity of(PPh3)RhCl uncovered its high activity as a homogeneous hydrogenation catalyst.This was the first homogeneous catalyst that compared in rates with heterogeneous counterparts.Wilkinsons original reportWilkinson hydrogenation:classic dihydride mechanismThe Holy Grail of CatalysisC-H Activation代表催化剂设计的最高目标代表催化剂设计的最高目标 C-H Activation:sp3C-H complexregioselectivity:sp2 C-H 1o sp3C-H 2o sp3 C-H 3o sp3 C-H.sp3C-H:concerted vs.radicalAgostic interactions:intramolecular-complex（1997年：元结；年：元结；2005年：抓氢键）年：抓氢键）Green,M.L.H.JOMC 1983(250)395 Agostic：缘自古希腊荷马史诗，由发现者英国教授Green提出中国石化张中岳中国石化张中岳：元结；译者为了保持agostic身上所带的古雅的文学内涵，撷取唐代大诗人李白和李商隐的名句中各一字组成“元结”二字，并取意“原结”，“原来就存在的一种结合作用”，以图古朴典雅，又比较达意。北大周公度北大周公度：抓氢键；“抓住使靠在身旁”Agostic interactionsJ.Am.Chem.Soc.1974,96,754-760.Agostic interactions：ApplicationC-C Activation:sp3C-sp3C complexbond dissociation energies(BDE)BDE(C-H)BDE(C-C):C6H5-H:110 kcal/mol vs.C6H5-CH3:100 kcal/mol TM mediated OAs into C-C bonds are much more rare than those for analogous C-H bonds.Formation of the-complex is kinetically disfavored by steric repulsion between the metal complex and the carbon substituents and by the high directionality of the sp3C-sp3C bond that localizes the bonding orbital deep between the carbon nuclei.Milstein JACS 2000(122)9848.Milstein OM 1997(16)3981.OA with Csp2-X bonds:aryl and vinyl halidesThree main mechanisms to consider for this process:Transmetalation(转金属转金属)Definition:The transfer of an organic group from one metal center to another.The process involves no formal change in oxidation state for either metal.Cross-CouplingReagent R X-coupling reactionLiR,MgXR vinyl,aryl,allyl,alkyl KumadaRZrClCp2 vinyl,alkylRZnCl vinyl,aryl,alkyl NegishiRCuLn alkynyl,aryl e.g.SonagashiraRSnR3 vinyl,aryl,alkynl StilleRB(OR)2 vinyl,aryl SuzukiR-9BBN alkyl Suzuki-MiyauraRSiR3 aryl,vinyl HiyamaAlR2,AlX2 alkyl In generalthe rates of transmetalation of R follow the order:alkynyl aryl,vinylalkylTransmetalation Mechanism：the least-studied of the basic reaction steps.In a simple picture,the metal accepting the R group is the electrophile and the M-R bond being transferred is the nucleophile.M-R bond formation may or may not be simultaneous with M-X bond formation,depending on the nature of X and the actual complexes involved.With this model,increasing the nucleophilicity of R by altering the ligands on M and increasing the electrophilicity of M through its ligands will facilitate the transmetalation step.For weakly nucleophilic transmetalation reagents,an addednucleophile or base often facilitates the transmetalation.Transmetalation with the Suzuki coupling often requires added baseF-is thought to activate the organosilicon reagent for transmetalation via formation of a nucleophilic pentavalent silicate in a Hiyama couplingReductive Elimination促进还原消除的因素促进还原消除的因素1)1)、吸电子烯烃；、吸电子烯烃；2)2)、COCO（酸）；酸）；3)3)、加热；、加热；4)4)、正电荷有利于还原消除；、正电荷有利于还原消除；5 5）、）、Bite Angle Effects Bite Angle Effects（咬角效应）（咬角效应）插入和反插入反应插入和反插入反应（Migratory Insertion/De-insertion）Mechanism for CO insertion:via alkyl migration to coordinated CO-Hydride EliminationWacker OxidationWacker OxidationReagent R X-coupling reactionLiR,MgXR vinyl,aryl,allyl,alkyl KumadaRZrClCp2 vinyl,alkylRZnCl vinyl,aryl,alkyl NegishiRCuLn alkynyl,aryl e.g.SonagashiraRSnR3 vinyl,aryl,alkynl StilleRB(OR)2 vinyl,aryl SuzukiR-9BBN alkyl Suzuki-MiyauraRSiR3 aryl,vinyl HiyamaAlR2,AlX2 alkyl In generalthe rates of transmetalation of R follow the order:alkynyl aryl,vinylalkylCross-Coupling Reactions：C-C Bond FormationKumada CouplingChatt and Shaw J.Chem.Soc.1960 1718.Yamamoto JOMC 1970(24)C63.Its just over there,waiting for the right people.Kumada,the right people!清清除除