齐格勒-纳塔催化剂让聚乙烯有什么不同？
How did Ziegler–Natta catalysts change polyethylene?
它能在温和条件下让乙烯按规整方式聚合，得到密度高、强度好的聚乙烯，也催生了聚丙烯，彻底改变了塑料工业。
It lets ethylene polymerize in a regular, controlled way at mild conditions, giving strong high-density polyethylene and enabling polypropylene—transforming the plastics industry.
难度 专业 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
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Housecroft & Sharpe,《Inorganic Chemistry》第5版,Pearson,2018
C. E. Housecroft and A. G. Sharpe, Inorganic Chemistry, 5th ed., Pearson, 2018
#齐格勒纳塔 #聚合 #催化剂
钯催化交叉偶联反应中,为什么要加入碱?碱起什么作用?
In palladium-catalyzed cross-coupling reactions, why is a base added and what role does it play?
偶联循环中氧化加成后生成的有机钯物种需要与亲核试剂转金属化,而转金属化通常要求亲核试剂以负离子或中性的富电子形式存在。碱的作用是中和氧化加成产生的卤化氢,并把硼酸及其酯转化为更易转移的四配位硼酸根等活性物种;Negishi 反应中的有机锌试剂本身即为活性亲核体,通常无需外加碱。没有碱,转金属化速率极慢,催化剂停留在Pd(II)中间体而失活,偶联产率大幅下降。
After oxidative addition, the organopalladium species must undergo transmetalation with the nucleophilic partner, which generally requires the nucleophile in an anionic or electron-rich neutral form. The base neutralizes the HX generated in oxidative addition and converts boronic acids and esters into readily transmetalating tetrahedral boronate species; organozinc reagents in Negishi couplings are themselves active nucleophiles and usually need no added base. Without base, transmetalation is extremely slow, the catalyst stalls at a Pd(II) intermediate and decomposes, and coupling yields collapse.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-04
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Suzuki,《Synthetic studies via the cross-coupling reaction of organoboron derivatives with organic halides》,Pure and Applied Chemistry,1991 (DOI: 10.1351/pac199163030419)
Suzuki, 'Synthetic studies via the cross-coupling reaction of organoboron derivatives with organic halides', Pure and Applied Chemistry, 1991, DOI: 10.1351/pac199163030419
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1351/pac199163030419
#交叉偶联 #转金属化
Wilkinson 催化剂 RhCl(PPh3)3 催化烯烃加氢的启动步骤是什么?为什么 PPh3 配体的数量必须不多不少?
What initiates alkene hydrogenation by Wilkinson's catalyst RhCl(PPh3)3, and why must the count of PPh3 ligands be neither too high nor too low?
循环从一个 PPh3 解离开始,生成 14 电子、配位不饱和的 RhCl(PPh3)2 活性物种,随后依次发生 H2 氧化加成、烯烃配位、迁移插入和还原消除。PPh3 过多时解离平衡左移,活性物种浓度低,加氢速率下降;PPh3 过少时低配位铑碎片倾向二聚甚至析出铑黑而失活。配体解离平衡因此同时决定催化活性与催化剂寿命。
Each cycle starts with dissociation of one PPh3, generating a coordinatively unsaturated 14-electron species RhCl(PPh3)2 that proceeds through oxidative addition of H2, olefin coordination, migratory insertion, and reductive elimination. With excess phosphine the dissociation equilibrium shifts left, the active-species population drops, and hydrogenation slows. With too little phosphine, underligated rhodium fragments dimerize or precipitate as inactive rhodium black; this ligand dissociation balance governs both activity and lifetime of the catalyst.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-04
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Osborn、Jardine、Young 与 Wilkinson,《The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives》,J. Chem. Soc. A,1966 (DOI: 10.1039/j19660001711)
Osborn, Jardine, Young & Wilkinson, 'The preparation and properties of tris(triphenylphosphine)halogenorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives', J. Chem. Soc. A, 1966, DOI: 10.1039/j19660001711
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1039/j19660001711
#均相加氢 #氧化加成
Suzuki-Miyaura 偶联的钯催化循环包含哪几个基本步骤？为什么芳基卤与 Pd(0) 的氧化加成常被认为决定了底物的反应活性？
What are the elementary steps of the Suzuki-Miyaura coupling cycle, and why is oxidative addition between the aryl halide and Pd(0) usually regarded as the step that dictates substrate reactivity?
循环由氧化加成、碱辅助的硼酸转金属化和还原消除三步构成，后者生成联芳基 C-C 键并再生 Pd(0)。C-I 与 C-Br 键远比 C-Cl 容易氧化加成，故碘代、溴代芳烃在温和条件下即可偶联，而氯代物需要 SPhos 等富电子大位阻配体活化。碱一方面把硼酸转成四配位硼酸根以促进转金属，另一方面清除卤化氢，因此 K2CO3 与 K3PO4 的选择会明显影响收率与副产物。
The cycle runs through oxidative addition of the aryl halide to Pd(0), base-assisted transmetalation from the arylboronic acid, and reductive elimination that forms the biaryl C-C bond and regenerates Pd(0). Aryl iodides and bromides add oxidatively far more readily than aryl chlorides, so they couple under mild conditions whereas chlorides require electron-rich bulky ligands such as SPhos. The base both converts boronic acids into tetrahedral boronate species primed for transmetalation and scavenges HX, which is why choosing K2CO3 over K3PO4 measurably shifts yield and byproduct formation.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Miyaura N, Suzuki A，有机硼化合物的钯催化交叉偶联反应（综述），Chemical Reviews，1995 年第 95 卷
N. Miyaura, A. Suzuki, Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds, Chemical Reviews, vol. 95, p. 2457 (1995)
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1021/cr00039a007：Palladium-Catalyzed Cros
#金属有机催化 #交叉偶联