金属有机化学名师优质课赛课一等奖市公开课获奖课件.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,第三章 氧化加成反应,Chapter 3 Oxidative Addition,第1页,氧化加成反应,是指基团,A-B,对过渡金属络合物中心金属加成反应。,从电子改变看：能够有双电子和单电子氧化加成，加成结果是使金属中心发生氧化：,第2页,氧化加成是描写反应过程化学计量关系，还没有指明特定机理,氧化加成反应是生成金属,-,碳和金属,-,氢键主要方法，也是,C-H,键活化所包括到主要基元反应。所以对这类基元反应范围和历程讨论是过渡金属有机化学主要内容。,一、反应范围及影响原因,第3页,1.,价电子构型,对全部含有价电子数,2,4,6,7,8,10,构型过渡金属络合物都存在氧化加成，不过对中心金属含有,d,8,d,10,电子构型络合物最为普遍。,2.,配合物类型,配位饱和和配位不饱和络合物都能够发生氧化加成反应，不过配位不饱和络合物更为活泼。,第4页,配位饱和,d,8,电子构型配合物采取三角双锥构型,第5页,3.,加成物分类,（,1,）极性亲电试剂：,X,2,H-Y,RSCl,RSO,2,Cl,R-X,RCOX,RfI,R-CN,SnCl,4,HgX,2,这类试剂加成方式与对烯烃加成类似，能够按极性两步历程或链式自由基历程进行。,（,2,）加成试剂在加成后仍有键连接,O,2,S,2,Se,2,邻笨醌，,RC,CR,RN=NR,RCH=CHR,S=C=S,CH,2,=O,环丙烷，,1,，,3-,偶极加成物，如：,RCON,3,RN,3,第6页,第二类试剂，因在加成后保留有键，所以新形成两个键必须是顺式。底物限于配位不饱和络合物，或加成前失去一个配位体得到配位不饱和络合物。,（,3,）非极性加成试剂,这类试剂有：,H,2,R,3,Si-H,R,3,Ge-H,RSH,RCHO,Ar-H,R-H,活化,C-H,基团氧化加成,这类试剂通常仅与配位不饱和络合物进行加成，而且总立体化学是立体专一顺式加成。但也有例外：在质子碱存在下配位饱和络合物氢化。,第7页,4.,金属中心,不一样金属,d,8,络合物对氧化加成相对活性与其发生氧化加成形成,d,6,电子构型倾向性相关,第8页,5.,配体,配体改变时，相对活性会有改变。释电子配位体如瞵增加氧化加成倾向，而,-,授体如,CO,或烯烃减低氧化加成倾向。,二、各类氧化加成反应历程,（一）生成,M-C,键氧化加成反应,第9页,A.,双电子过程机理,反应特点：,需要金属配合物配位不饱和,碳构型保持不变,氧化加成两个基团在金属中心保持顺式,常见是卤代烃加成,1.,协同机理,(concerted mechanism),第10页,2.S,N,2,机理,反应特点：,碳构型翻转,阳离子型中间体,遵照二级反应动力学,含有经典,S,N,2,反应特征,第11页,B.,单电子机理,1.,原子攫取及另外一个金属中心结合,反应特点：,M,n,与,RX,化学计量关系为,2,：,1,氧化加成试剂碳外消旋化,Rate=K,obs,MRX,tertiary C secondary C primary C Methyl,EPR,能够检测到,R,.,第12页,2.,自由基链式历程,(Radical chain pathway),反应特点,evidence for R,(racemization,homocoupling,traping),Initiation and inhibition.,第13页,3.,内界电子转移（或笼状自由基对）机理,第14页,反应特点：,Similar to S,N,2,but should give racemization at carbon,4.,外界电子转移机理,第15页,反应特点：,发生反应时能垒较高,只有在内界电子时配位受阻，,S,N,2,反应相对较慢。,第16页,1.,平面,d,8,电子构型,Ir,I,络合物,L,为有机膦配体,JACS,1966,88,3511,第17页,(1),络合物中膦配体不一样反应速度有以下降低次序,PMe,2,Ph PEt,3,PEt,2,Ph PEtPh,2,P(,p,-C,6,H,4,CH,3,),3,PPh,3,P(OPh),3,PMe,2,Ph PEt,3,反应速度相差,1.5,倍,从,PEt,3,到,PPh,3,反应速度相差,30,倍,PPh,3,P(OPh),3,之间反应速度相差,20,倍,给电子能力越强，增加金属中心发生氧化加成转变成,d,6,电子构型倾向,给电子能力强膦配体增加中心金属活性，给电子能力弱配体降低活性。,第18页,（,2,）络合物中基团,Y,为,F Cl Br I,时反应速度依次降低。,说明空间原因起主要作用。,（,3,）,CH,3,-X,中,X,为,I Br Cl,速度也依次降低。,CH,3,-X,中,X,越易离去反应速度越快。,CH,3,I CH,3,CH,2,I R,2,CHI R,3,CI,（,4,）溶剂极性对反应速度影响次序,DMF CH,3,CN THF C,6,H,5,Cl C,6,H,6,极性越大，,C-X,中,X,越易离去。,第19页,（,5,）反应不受自由基去除剂影响，动力学研究表明反应服从二级速率公式,（,6,）二级卤代烷对这个反应不活泼,第20页,（,7,）反应过程中观察不到,X,与外加卤负离子交换。说明反应是受动力学控制。,（,8,）手性卤代烷,R*X,在反应过程中发生构型翻转。是,S,N,2,历程主要证据之一。,极性溶剂使反式产物重排为热力学稳定顺式产物,第21页,手性,R*-X,在这么加成中发生构型翻转。,二级卤代烷对平面四方,d,8,Ir,I,络合物氧化加成是按照自由基历程进行，能够从手性,R*-X,发生外消旋化得到证实。,L=PMe,3,or PMe,2,Ph,这个反应给出了,(R,R),和,(R,S)-,两种构型产物,第22页,下式为自由基引发各步骤，每个过程相当于单电子改变自由基加成。,第23页,由上述情况能够看出：,d,8,Ir,I,络合物氧化加成有,S,N,2,历程和链式自由基历程。,与,CH,3,I,反应按照,S,N,2,历程进行，而二级卤代烷和其它一级卤代烷活性都不足以按照,S,N,2,历程进行。,第24页,Relative reactivity:ROTs PhBr(80,0,C PhCl(no reaction at 135,0,C),Electron donating groups slow down the rate of oxidative addition,electron withdrawing groups accelerate the reaction.,PhCl(no reaction at 135,0,C),p,-Clbenzophenone(89%,135,0,C)p-chlorobenzonitrile,(97%,100,0,C),二级烷基,新戊基,X=OTs I Br Cl,立体化学：氧化加成试剂碳立体构型发生翻转,反应属于,S,N,2,历程,第41页,（二）生成,M-H,键氧化加成反应,H,2,对过渡金属络合物氧化加成是不饱和烃氢化，氢甲酰化，费,-,托反应等催化循环中必不可少步骤。,H,2,氧化加成大多数是可逆。,第42页,第43页,1.Concerted mechanism,Vaskas complex(JACS,1985,107,8049),Rate=K,obs,IrH,2,k,H,/k,D,=1.09,Stereochemistry of oxidative addition:When H,2,adds to a square planar complex,it can add,along two different L-M-L axes.,第44页,In the case of a chelated version of Vaskas complex,a stereoselective addition was seen.The H,2,approaches along the P-M-CO axis.,第45页,H,2,The-acceptor orbital of CO helps to stabilize the H,2,complex promoting oxidative addition along that axis.,第46页,The Kubas dihydrogen complex undergoes reversible oxidative addition to give the dihydride(,JACS,1986,133,9,).A variable temperature NMR study showed that at 50,C,the,1,J,H-D,disappears reversibly.,第47页,Serena Fantasia,et al,Angew.Chem.Int.Ed,.,DOI:10.1002/anie.00463,第48页,2.Homolytic Cleavage of Hydrogen,Although less common,there are examples of 17 e metal complexes oxidatively adding H,2,by a homolytic mechanism.,rate=kobs(CN),5,Co,3-,2,H,2,Halpern,Inorg.Chem,.1970,9,2616;,Inorg.Chim.Act,.1983,77,L105-L106,第49页,3.Heterolytic Cleavage,Activation of H,2,by heterolytic cleavage is not formally an oxidative addition.The metal retains,the same oxidation state and coordination number in the product.A base,either external or one of the ligands,promotes the heterolytic cleavage by deprotonating the bound H,2,ligand.,An example is this hydride bridged Ru dimer,where the oxygen acts as a base to promote H,2,addition to give the hydroxy Ru-H.,C.P.Casey,JACS,123,1092.,第50页,Heterolytic oxidative addition of H,2,promoted by an external base is a key step in many ionic hydrogenation catalysts.,第51页,Participation by an internal ligand is very Common for,early transition metals,activation by an external base is less commonly observed.,H,2,第52页,Sc(III)is d,0,metal,so this reaction cannot involve oxidative addition of dihydrogen.Instead the reaction occurs by a process called,-bond metathesis,.,第53页,(,三,)Oxidative addition of Silanes(Si-H),Silanes typically undergo oxidative addition by,a concerted mechanism,and show similar reactivity to H,2,.,Oxidative addition of silanes is,a general method,for the preparation of metal-silyl complexes and is the initial step in hydrosilylation catalysts.,JACS,1985,107,1794,第54页,(,四,)Oxidative addition of Alkanes(C-H),Same mechanisms as H,2,Oxidative addition,Heterolytic:M-Z+H-CR,3,M-CR,3,+HZ,Homolytic:2 M,n,+H-CR,3,M,n+1,-CR,3,+M,n+1,-H,Concerted:M,n-,+H-CR,3,(alkane complex),H-M,n+2,-CR,3,General trend:sp,2,C-H bonds are usually activated more readily than sp,3,C-H bonds.,第55页,1.Heterolytic cleavage:-bond metathesis,Early transition metals(usually d,0,)with basic ligands(H-,R-)will heterolytically activate C-H bonds.For d,0,metals,oxidative,addition is not possible,so the reaction must proceed by-bond metathesis.,Acc.Chem.Res,.,1985,51,第56页,Is the mechanism simply electrophilic aromatic substitution?,第57页,2.Homolytic Activation,2(TMP)Rh+CH,4,(TMP)RhH+(TMP)RhCH,3,Proposed mechanism,J.Am.Chem.Soc,.,1991,113,5305,第58页,3.Concerted Oxidative Addition,a.Intramolecular C-H oxidative addition,Intramolecular oxidative addition,which is often called cyclometallation,is very common.,J.Am.Chem.Soc,.1969,91,6983,Prior coordination(agostic)allows the weakly binding C-H species to be held in close proximity to the metal center facilitating oxidative addition.,第59页,b.Intermolecular C-H oxidative addition,The first examples of intermolecular oxidative addition of alkanes was reported by Bergman(J.Am.Chem.Soc.,1982,104,352 and 1983,105,7190)using coordinatively unsaturated iridium(I)complexes formed by expulsion of H,2,.,第60页,Cp*Ir(PMe,3,)+H-Cy,第61页,For alkanes,less sterically hindered C-H bonds add at faster rate.,This presumably is due to the greater stability of less sterically demanding alkane complexes.,Oxidative addition of arenes is generally preferred over oxidative addition of alkanes.,Arene C-H:110 kcal/mol;Alkane C-H:95 kcal/mol,第62页,第63页,The importance of prior coordination has been studied by various authors for systems similar to Bergmans Ir,I,complex.,第64页,J.Am.Chem.Soc,.1982,104,4240.,J.Am.Chem.Soc,.,123,12724-5,Kinetic studies appear to confirm the intermediacy of an arene complex.,J.Am.Chem.Soc,.,123,12724-5,第65页,J.Am.Chem.Soc,.,1997,119,10235-7,第66页,（五）,C-H,键氧化加成为控制步骤催化循环,1.Benzene-D,2,交换,奇数价电子过渡金属有机配合物能够催化,benzene-D,2,交换。这些化合物如,(C,5,H,5,),2,NbH,2,，,(DMPE),2,TaH,5,(Ph,3,P),3,ReH,5,(C,5,H,5,)(,-,C,5,H,5,)NbH,2,(C,5,H,5,),2,(PR,3,)TaH,等表现出一级同位素效应。,k,H,/k,D,=23,表明反应决速步骤有,C-H,键断裂。,第67页,第68页,2.(C,5,H,5,),2,Nb(CH,2,CH,3,)(CH,2,=CH,2,),在,benzene-,d,6,中重氢交换反应,第69页,3.(C,5,H,5,)Rh(C,2,H,4,),2,中乙烯在,benzene-,d,6,中重氢交换反应,第70页,上述配合物中乙烯配体完成交换后，环戊二烯配体也能够进行重氢交换反应。,请大家自己设计该反应催化循环。,提醒：,分子间,C-H,键加成,第71页,