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
13
O
13
CO
CO COCO CO NhomakorabeaMn CO
• 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 control (I.e. the first-formed product is observed).
13
Me
13
“Me moves”
CO
CO
Experiment shows mixture of cis and trans in ratio 2:1 so ALKYL MIGRATION is the mechanism
CO CO
Expected products of methyl (de)migration (a non-13C product is also formed)
• Unfortunately the term “1,1-elimination” etc. is rarely used, even though it’s the opposite of a 1,1-insertion!
1,1-Migratory Insertion and -Elimination
» metallacycle, or unstable alkene product
• Sometimes, the “transition state” is an intermediate; giving the agostic interaction…(see “organometallic hypertext book”)
13
Me OC Mn OC CO
13
CO CO
O CO CO
Expected product of CO “deinsertion” (a non-13C product is also formed)
CO Me Mn OC CO CO
13
or
, -CO
CO OC Mn OC CO CO OC Mn Me CO
1,1-Migratory Insertion and -Elimination
Insertion or Migration?
Study reverse reaction, then apply Principle of Microscopic Reversibility
“CO moves”
, -CO Me OC Mn OC CO
X：卤素
络合物128中的Cr(CO)3由于向三个CO 提供反 馈电子，成为一个有一定吸电子能力的基团， 使苯环上的电子云密度下降，使原来只能接受 亲电进攻的苯环可接受亲核进攻。
CO的反应活性不高，但与金属配位后，金属反馈的 电子使碳上的电子云密度降低，而易接受亲核进攻。
氧上的电荷密度增加，变得可接受亲电进攻。
18 VE
X M A1 B2 18 VE
1,2-migratory insertion
M A
B
A=B is often an alkene
16 VE
• Numbering describes which atoms of the inserted ligand are bonded to M and X after the insertion • Opposite of insertion is elimination (or “deinsertion” in USA)
• 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 reaction (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…
Definitions; Elimination - E
X M A 18 VE B
-elimination
(1,1-elimination) M
X

A B
16 VE X
X M A B 18 VE
-elimination
(1,2-elimination) M A
B


16 VE
• This is the same as the last slide with arrows going backwards • Named by which atom contains the migrating group
• β-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 -Elimination
Preventing -elimination
• Although -elimination is slightly endothermic, it is a common decomposition pathway for alkyls
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，炔烃反键轨道的电子反馈，使双或三 键活化，可接受外来亲核试剂的进攻，进攻的 方向是在烯烃或炔烃与金属配位的反面
1,2-Migratory Insertion and -Elimination
Definitions and conditions
1,2-migratory insertion
LnM H LnM H LnM H

CN = n+2
coplanar 1,2- or b-elimination
CN = n+1
The reaction on Slide 15 is also consistent with alkyl migration, not CO insertion
脱羧反应：CO插入的逆反应
烯烃的插入和β-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
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 -Elimination
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 -Elimination
Where does the CO come from?
Me CO Mn CO CO CO CO Me
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 -Elimination
1,1-Migratory Insertion and -Elimination
Is this a cis process?
Me Me
13 13
O C CO Mn CO CO

13
O C Cl +
[Mn(CO)5]-
CO CO
, -CO
CO Me
CO Mn CO CO
CO
only cis isomer
• Can be prevented by – not having any -hydrogens ( a very effective strategy!) – saturating the coordination sphere (i.e. no free coordination site available) – preventing planarisation
CO insertion or “CO moves”