配位催化反应.ppt

1、第8章 配位催化反应,有机金属化合物的应用,本章要点: 一. 过渡金属有机化合物的基本反应二. 配位催化反应,均相催化反应，有机金属化合物参与，经过一系列反应 起催化作用的有机金属化合物必须是配位不饱和（coordinative unsaturation) 起始物有活性 ( activated precursors ) 加热时配体可失去, Tolman锥角大( 例如, PPh3, 145) RhCl(PPh3)3 RhCl(PPh3)2 + PPh3 (25 C) K=2.3107 T 2RhCl(PPh3)3 Rh2(Cl)2(PPh3)4,一、配位催化反应的要点,与给体 (donor)的酸

2、性强度大小有关 酸性小, 反馈键弱, 活性大 PPh3比CO和PCl3的酸性小, 活性大 RhCl(PPh3)3 +C2H4 RhCl (C2H4)(PPh3)2 + PPh3 (取代) 16e 16e RhCl(PEt3)3 +C2H4 RhCl (C2H4)(PEt3)3 (加成) 18e,配体L的大小决定配位数和反应活性 NiL4 NiL3+L 当L=PPh3时, 溶液中的NiL4全部解离为NiL3 配体L体积太大，不易与金属离子配位 配体L体积太小，形成的配合物太稳定，使催化循环反应不易进行,二、过渡金属有机化合物的基本反应,配体的解离和取代 氧化加成(oxidative additi

3、on) 还原消除(reductive elimination) 插入和迁移(insertion and migration） 对配体的亲核加成反应(nucleophilic addition to ligand),Ligand substitution,The substitution of ligands in organometallic complexes is very similar to the substitution of ligands in coordination complexes, with the additional constraint that the val

4、ence electron count at metal atom does not increase above 18; steric crowding of ligands increases the rate of dissociative processes and decreases the rate of associative processes.,氧化加成反应(oxidation addition) (配位不饱和) 氧化态在加成反应过程中是否改变? 非氧化加成 PF5 + F PF6 ( 氧化态不变, 非氧化加成) PdCl4 2 + Cl PdCl5 3 ( 氧化态不变, 非

5、氧化加成) TiCl4 + 2POCl3 TiCl4(POCl3)2,氧化加成: Fe(CO)5 + H+ Fe(CO)5H+ ( 质子化, 氧化态由0 +2) Mn(CO)5 + H+ Mn(CO)5H ( 质子化, 氧化态由 1 +1) PF3 + F2 PF5 ( 氧化态由+3 +5) SnCl2 + Cl2 SnCl4 ( 氧化态由+2 +4),与金属有机配合物发生氧化加成的试剂 XX H2, Cl2, Br2, I2, (SCN)2 HX HCl, HBr, HI, NH3, HCOOR, RCHO C X CH3I, C6H5Br, CH3COCl,(1) 保持 X X, 例如:,

6、+1 +3,X X键 断开 例:,(3). 已经是18电子构型的, 氧化加成时排除一个配体，保持18电子结构 例: Ru(CO)4(PMe3) + CH3I 18e ( 0 ) Ru(CH3)(I)(CO)3 (PMe3) + CO 18e (+2),还原消除反应(Reductive Elimination Reactions) 氧化加成反应的逆过程 (氧化态降低),(+4) (+2),H消除 ( 氧化数不变, 配位数不变), agostic H,（其中的LnM表示n个配体L）,氧化加成和还原消除反应的一般规律 （其中的LnM表示n个配体L）,Oxidative addition and re

7、ductive elimination,Oxidative addition occurs when a molecule X-Y adds to a metal atom to form new M-X and M-Y bonds with cleavage of X-Y bond; oxidative addition results in increasing the coordination number of metal atom by 2 and increasing the oxidation number by 2; reductive elimination is the r

8、everse of oxidative addition.,过渡态 或中间体 或产物,起始物,产物,协同加成反应示意图,3. 插入反应(insertion) 或迁移反应(migration),酰基化 氧化态配位数,Carbonyl insertion or alkyl migration,烯烃的1, 2 插入反应,vacant site,site available,Ziegler-Natta 反应合成高聚物,CO插入,SO2插入,CO直接插入 CO in COCH3,CO分子内插入 CO cis to -COCH3,CH3迁移 CO cis to -COCH3,Mn(CO)5CH3与13CO

9、反应没有得到13C在酰基位置,CO插入反应的可能途径,加热脱CO的可逆反应中,cis trans 甲基迁移,Ref. T.C. Flood, et al., JACS, 1981,103,4410,The principle of microscopic reversibility:正反应和逆反应有相同 的反应路径。 结论：该羰基的插入反应为实际是甲基的迁移反应,插入反应: 烷基化,讨论: 加成反应、消除反应和插入反应是否改变氧化态?是否改变价电子数? 是否改变配位数？,1,1-Migratory insertion reactions,1,1-Migratory insertion reac

10、tions result from the migration of a species such as a hydride or alkyl group to an adjacent ligand such as carbonyl to give a metal complex with two fewer electrons on the metal atom, no change in the oxidation state.,1,2-Insertions and -hydride elimination,1,2-Insertion reactions are observed with

11、 2 ligands such as alkenes and result in the formation of an1 ligand with no change in oxidation state of the metal; -hydride elimination is the reverse of 1,2-insertion.,三、催化反应,多相催化(Heterogeneous or multiphasic catalysis ),高比表面 载体,均相催化(homogeneous or uniform catalysis),催化循环,催化反应与非催化反应的能量关系图,稳定中间体,W

12、ilkinsons catalyst : RhCl(PPh3)3,烯烃加成 Wilkinson 氢化反应 ( hydrogenation) RCH=CH2+H2 RCH2CH3,H2的氧化加成,L消除,H迁移,L加成,H插入， 还原消除,Hydrogenation of alkenes,Wilkinsons catalyst, RhCl(PPh3)3, and related complexes are used for the hydrogenation of a wide variety of alkenes at pressures of hydrogen close to 1 atm

13、or less; suitable chiral ligands can lead to enantioselective hydrogenations.,16e，四配位,H转移 烯烃加成,用HCo(CO)3作催化剂由丙烯醇制备丙醛的催化循环 CH2=CHCH2OH CH3CH2CHO,18e，五配位,16e，四配位,H消除,用HCo(CO)3作催化剂的加氢甲酰化反应 (hydroformylation) CH3CH2CH=CH2 +H2+CO CH3CH2CH2CH2CHO,CO加成,烯烃加成,CO消除,酰基的取代和消除,CO插入,Hydroformylation,The mechanism

14、 of hydrocarbonylation is thought to involve a pre-equilibrium in which octacarbonyldicobalt combines with hydrogen at high pressure to give a monometallic species that brings about the actual hydrocarbonylation reaction.,由甲醇(碘甲烷)合成乙酸的催化循环(Monsanto反应) CH3I +CO CH3COI CH3COI +H2O CH3COOH+HI,CH3I氧化加成,

15、CH3迁移和溶剂合,CO取代,CH3COI还原消除,羰基化反应,Methanol carbonylation: ethanoic acid synthesis,Both rhodium and iridium complexes are highly active and selective in the carbonylation of methanol to form acetic acid.,乙烯氧化为乙醛的催化循环(Wacker过程) C2H2+O2+H2O CH3CHO,Wacker 过程中杂多酸（heteropolyanion)的氧化还原偶合反应,Wacker oxidation

16、of alkenes,The Warker process is used to produce acetaldehyde from ethene and oxygen; the most successful system uses a palladium catalyst to oxidize the alkene, with the palladium being reoxidized via a secondary copper catalyst.,上世纪50年代 德国的Ziegler 发现了乙烯聚合反应的催化剂TiCl4-AlEt3，催化过程中给出TiCl3 意大利的Natta 完成

17、了丙稀的立体选择性(stereospecific)聚合 烯烃聚合的Ziegler-Natta 反应过程 Ziegler Natta 催化剂,TiCl4-AlEt3体系催化下的Ziegler-Natta 反应的可能过程 nCH2=CH2 (CH2CH2) n,Alkene metathesis: Alkene metathesis reactions are catalysed bu homogeneous organometallic complexes that allow considerable control over product distribution; a key step

18、in the reaction mechanism is the dissociation of a ligand from a metal center to allow an alkene to coordinate. (Yves Chauvin, Robert Grubbs, and Richard Schrock shared the 2005 Nobel Prize for chemistry “for the development of the metathesis method in organic chemistry”) Palladium-catalysed C-C bond forming reactions: A number of palladium-catalysed coupling reaction are known; they all proceed through oxidative addition of reagents at metal center followed by the reductive elimination of the two fragments. (2010 Nobel Prize for chemistry) Asymmetric oxidations: Appropriate chiral lig