金属有机化合物的基元反应(2).ppt

1、金属有机化合物的基元反应,一般有四类基元反应 1 配体的配位和解离反应 2 氧化加成反应和还原消除反应 3 插入反应和消除反应（反插入反应） 4 和金属络合的配体被进攻的反应,插入反应与反插入反应,插入反应为不饱和键插入到M-H,M-C之间的反应。它主要有两种类型：1 AB分子插入后分别与金属和R基团相连。2 AB分子插入后A同时与金属和R基团相连,Definitions; Migratory Insertion - MI,Numbering describes which atoms of the inserted ligand are bonded to M and X after the

2、 insertion Opposite of insertion is elimination (or “deinsertion” in USA),A=B is often CO,A=B is often an alkene,Definitions; Elimination - E,This is the same as the last slide with arrows going backwards Named by which atom contains the migrating group Unfortunately the term “1,1-elimination” etc.

3、is rarely used, even though its the opposite of a 1,1-insertion!,1,1-Migratory Insertion and a-Elimination Stereochemistry at carbon,Configuration at a stereogenic carbon is retained Same applies to the reverse, i.e. a-elimination,CO的插入反应:,由于CO和金属配位，金属的d电子向CO的反键轨道反馈，导致M-R键的削弱，同时CO中的碳-氧键也被削弱。 插入反应这一过

4、程有两种可能的途径 1 CO 插入到M-R键中 2 与金属相连的R基团迁移到CO上,1,1-Migratory Insertion and a-Elimination Mechanistic questions,The above reaction has been studied in detail, and much is known about the mechanism,研究表明是按R基团迁移的的途径进行的R基团迁移不可能得到4，研究表明产物1：2：3的比率为1：2：1，而且没有4 生成。,1,1-Migratory Insertion and a-Elimination Where

5、does the CO come from?,CO that is inserted into Mn-Me bond is “unlabelled”, so it must have come from within the complex (i.e. mechanism is intramolecular) The 13CO in the product has remained cis to acyl and has not moved at all to the trans site. In other words, the reaction is under kinetic contr

6、ol (I.e. the first-formed product is observed).,1,1-Migratory Insertion and a-Elimination Is this a cis process?,The 13C labelled acyl product was synthesised by an alternative route shown above, and was then heated to promote elimination Only the cis isomer was observed, therefore in the reverse re

7、action (the 1,1-MI) the methyl group must be reacting with a CO that is cis to it. This logic relies on the Principle of Microscopic Reversibility In a single step reversible reaction, the mechanism of the forward reaction is the same as that of the reverse reaction,1,1-Migratory Insertion and a-Eli

8、mination Which Moves? The CO or the Me?,The two products are the same, so how do we tell which mechanism is happening?,Consider the two possibilities,1,1-Migratory Insertion and a-Elimination Insertion or Migration?,Expected product of CO “deinsertion” (a non-13C product is also formed),Expected pro

9、ducts of methyl (de)migration (a non-13C product is also formed),Experiment shows mixture of cis and trans in ratio 2:1 so ALKYL MIGRATION is the mechanism,Study reverse reaction, then apply Principle of Microscopic Reversibility,The reaction on Slide 15 is also consistent with alkyl migration, not

10、CO insertion,“CO moves”,“Me moves”,脱羧反应：CO插入的逆反应,烯烃的插入和-H消去,烯烃的插入反应的前提条件是烯烃与金属中心离子配位反馈，导致烯烃的活化和M-R键的削弱，结果生成C-R键和新的C-M 键，这种加成一般是顺式加成,1,2-Migratory Insertion and b-Elimination Definitions and conditions,Change in CN = -1 for 1,2-MI, but no change in OS Free coordination site needed for b-elimination B

11、oth forward and reverse reactions go through a planar transition state,CN = n+2,1,2-migratory insertion,1,2- or b-elimination,CN = n+1,coplanar,-H消去一般有以下4步1，有空配位-配体解离2，M-C和C-H共平面3，消除生成双键 4，生成的双键解络,1,2-Migratory Insertion and b-Elimination Preventing b-elimination,Although b-elimination is slightly e

12、ndothermic, it is a common decomposition pathway for alkyls Can be prevented by not having any b-hydrogens ( a very effective strategy!) saturating the coordination sphere (i.e. no free coordination site available) preventing planarisation metallacycle, or unstable alkene product Sometimes, the “transition state” is an intermediate; giving the agostic interaction(see “organometallic hypertext book”),和金属络合的配体被进攻的反应,具有不饱和键的化合物通过不饱和键和金属配位后被活化。过渡金属与烯烃、N2、CO、CO2等小分子形成配位键后，弱化氮氮三键或碳氧三键，这是小分子活化的基础。,烯烃，炔烃与过渡金属配位后，由于金属原子对烯烃，炔烃反键轨道的