碳碳单键的形成反应-3

碳碳单键的形成反应-3有机过渡金属化学

概念Concepts

•配位化学Coordination Chemistry : The chemistry of transition metal complexes that

have noncarbon ligands (Werner complexes). Classification applies to the catalyst and all reaction intermediates.

OR = O i Pr

Allylic alcohol

t BuOOH

概念Concepts

•有机金属化学Organometallic Chemistry: The chemistry of metal complexes that have M-C bonds (organometallic complexes).

Classification applies to the catalyst and/or reaction intermediates.

Pd(PPh3)4

catalyst

有机过渡金属的重要性

•Organotransition Metal Chemistry :

Transition metal mediated reactions that solve (or have potential to solve) challenging problems in the synthesis of organic molecules.

过渡金属

碳碳单键的形成：

过渡金属催化的偶联反应

氧化加成

还原消除

转金属化

常用的Pd催化剂与配体

•常用的Pd催化剂有0价和+2价。

Pd(0): Pd(dba)2, Pd(PPh3)4

Pd(II): Pd(OAc)2, PdCl2(MeCN)2, PdCl2等

•常用的配体分为单齿(monodendate)和多齿(chelating)

过渡金属价轨道与18电子规则

18 electron rule: upper limit of 18 e-can be accomodated w/out using antibonding molecular orbitals (MO's).

配位/解离与氧化加成•Oxidative Addition (OA):

metal mediated breaking of a substrate σ-bond and

formation of 1or 2 new M-L σ bonds. OA requires

removal of 2 electrons from the metal's d electron count.

This is reflected in a two unit increase in the metal's

oxidation state.

氧化加成

•烯基卤代物和芳基卤代物与Pd的氧化加成速度很快；但烷基卤代物的加成速度慢，另外，如果氧化加成中间体在C-Pd键的β位有氢原子，易于发生消除反应生成烯烃，称为β –Η消除(β−Η elimination)。

过渡金属催化的偶联反应通常使用烯基卤代物或芳基卤代物

烯基卤代物的制备方法

MeCN/water

碳碳单键的形成：

过渡金属催化的偶联反应

转金属化

转金属化Transmetalation •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. Transmetalation is often a reversible process, with the equilibrium favoring the more ionic M-X bond .

♣Subsequent reactivity of one L n M-R species can drive the equilibrium in one direction. This is often exploited in cross-coupling reactions,

常用的转金属化试剂与相关反应

In general, the rates of transmetalation of R follow the order: alkynyl> aryl,vinyl>alkyl

还原消除Reductive Elimination •Reductive elimination is a key transformation in transition metal mediated catalysis, often representing the product forming step in a catalytic cycle.

•Orbitals with more s character are less directional and lead to better overlap in the transition state for reductive elimination (RE). Note: cis orientation of the ligands is required for RE to occur.