金属有机化学12 催化的交叉偶联反应及相关聚合反应

Cross Coupling Reaction
Oxidative Addition is the rate limiting step in many cross-coupling reactions,
particularly with less reactive bromide and chloride substrates
Br
ROH
O
R
Substrates Limitation:
R
Br

R
Alkenyl and aryl halide were considered as “inactive” substrates
Cross Coupling Reaction
- 2010 Chemistry Nobel Prize Awarded for Carbon-Bonding Technique
CCR： Crazy Chemists ! they use jewelry in their reaction
Pd
Cross Coupling Reaction
Metal Source
Nickel can catalyze many of the same reactions as palladium. Nickel is attractive because it is much less expensive than palladium. Nickel-based catalysts tend to be less active and general, however. Nickel is better at activating aryl chlorides than palladium in some cases, however. Platinum has shown no activity in cross-coupling chemistry. Rhodium(I) can catalyze similar cross-coupling reactions as can Cu(I), although these are not nearly as general as the Pd-catalyzed reactions
b-H elimination Reductive elimination of P-O
in the presence of hard oxygen anions
Cross Coupling Reaction
Metal Source
Reduction by an organometallic species
This is the major mechanism of reduction for couplings involving OM nucleophiles
Generation of Pd(0) colloids or nanoparticles
"Ligand free" catalyst systems are believed to be catalyzed by soluble Pd(0) clusters. These clusters are highly active, but tend to grow until they precipitate as unreactive precipitate (Pd black). The formation of insoluble Pd black is also the main deactivation mechanism for ligand supported catalyst systems
交叉偶联反应及共轭聚 合物的合成
胡爱国
教学大纲
背景知识
金属有机化合物的定义及金属有机化学发展历史
金属有机化合物中的结构和化学键
化合价、 氧化态、 d 电子数、 饱和度、有机配体、配位数和18电子规则 空间点群（Poiቤተ መጻሕፍቲ ባይዱt Group）、立体构型 价键理论（Valence bond Theory）、晶体场理论（Crystal Field Theory） 分子轨道理论（Molecular Orbital Theory）
Cross Coupling Reaction
Metal Source Palladium is the most widely used metal for cross-coupling.
Generally the palladium is supported by a ligand. Both Pd(0) and Pd(II) sources can be used, although the active species is Pd(0) in all cases
sp2-organohalides are the most commonly used substrates. In addition, triflates, tosylates, etc. have been explored in these reactions as well
Reactivity: both substrate and ligand are important
Phosphines: Phosphines remain the most widely used ligands Monodentate phosphines are usually the most effective ligands
Sterically demanding, electron rich phosphines have received increasing attention recently as they provide more effective catalysts for less reactive substrates, such as aryl chlorides G. C. Fu; J. F. Hartwig; M. Beller
Cross Coupling Reaction
Ligand
Phosphines: Specially designed
Air Stable Water-soluble
Bisphosphines: chelating ligands
Cross Coupling Reaction
Ligand
N-Heterocyclic Carbenes: N-heterocyclic carbenes (NHCs, Arduengo carbenes) have attracted increasing attention as ligands for cross-coupling reactions recently. NHCs are stronger electron donors than phosphines and they tend to have stronger M-L bonds, thus they may give more stable catalysts.
Tiffany
Toltec
Nickel
Platinum
Rhodium
Cupper
Cross Coupling Reaction
Metal Source
Pd(II) sources are popular as they are less expensive and more stable than Pd(0). Pd(II) precursor can be reduced in situ via the following mechanisms Reduction by an amine or alcohol
Period Table
Organometallic compounds are normally named as substituted metals, e.g. alkyl metal or alkyl metal halide.
Group X metal complexes are used in cross coupling reactions
Cross Coupling Reaction
Reductive Elimination is usually a fast step in the catalytic cycle, so there is
less focus on designing ligands to promote it. RE is favored by electron deficient ligands (opposite of OA) and sterically demanding ligands (same as OA) Very sterically demanding ligands, such as (t-Bu)3P, can even induce RE of ArX
The rate of oxidative addition is: ArI > ArBr > ArCl. Aryl(alkenyl) triflates generally fall between iodides and bromides Activated (EWG) aryl halides will be at the low temperature end, while deactivated (EDG) aryl halides will be at the high end (recall Class 7 OA/RE)
Cross Coupling Reaction
Ligand
Although Palladium alone can catalyze cross-coupling reactions, ligands are usually necessary to give more active catalyst systems stabilize the Pd0 intermediate solubilize the catalyst increase the rate of OA
金属有机化合物的反应
配合反应 氧化加成反应和还原消除反应 （Oxidative Addition & Reductive Elimination） 迁移插入和消除反应（Migration Insertion & Elimination）、配体上的反应
金属有机化学在高分子合成中的应用
阴离子聚合反应 (Anionic Polymerization) 配位聚合反应 (Coordination Polymerization) 卡宾配合物和烯烃复分解聚合反应（Olefin Metathesis Polymerization） 交叉偶联反应及相关聚合反应 (Cross Coupling Polymerization) 原子转移自由基聚合反应(Atom Transfer Radical Polymerization) 金属有机高分子化合物（新型功能高分子）
Cross Coupling Reaction
Cross Coupling Reaction Developed in Last Three Decades
Cross Coupling Reaction
General Mechanism OA & RE
With the exception of the Heck reaction, all of these coupling reactions follow the same general catalytic cycle: 1) oxidative addition of the organic halide; 2) ligand substitution of the nucleophile for the halide; 3) reductive elimination of the new organic product
Nucleophilic Substitution
Classic SN2 and SN1 substitution
SN2
SN1
Nucleophilic Substitution
Williamson Synthesis
Br OK
- +
SN2
O
O-K+
Br
O
E1
Alkynylation:
Br H TMS nBuLi TMS