Ruthenium-catalyzed azide-alkyne cycloaddition: Scope and mechanism
Ruthenium-catalyzed azide-alkyne cycloaddition: Scope and mechanism
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DOI：
10.1021/ja0749993
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发表时间：
2008-07-16
影响因子：
15
通讯作者：
Fokin, Valery V.
中科院分区：
文献类型：
--
作者：
Boren, Brant C.;Narayan, Sridhar;Fokin, Valery V.
研究了一系列钌配合物在叠氮-炔环加成反应中的催化活性。[Cp* RuCl]络合物，如Cp* RuCl（PPh（3））（2）、Cp* RuCl（COD）和Cp* RuCl（NBD），是最有效的催化剂之一。在催化剂Cp* RuCl（PPh（3））（2）或Cp* RuCl（COD）的存在下，伯叠氮化物和仲叠氮化物与含有一系列官能度的宽范围的末端炔反应，选择性地产生1，5-二取代的1，2，3-三唑;叔叠氮化物的反应性明显较低。这两种配合物还促进有机叠氮化物与内部炔的环加成反应，提供获得完全取代的1，2，3-三唑的途径。铼催化的叠氮化物-炔环加成反应（RuAAC）似乎是通过叠氮化物和炔反应物的氧化偶联进行的，得到六元的叠氮化物中间体，其中第一个新的碳-氮键在炔的电负性更强的碳和叠氮化物的末端亲电氮之间形成。该步骤之后是还原消除，其形成三唑产物。DFT计算支持这一机制的建议，并表明还原消除步骤是速率决定。
The catalytic activity of a series of ruthenium(II) complexes in azide-alkyne cycloadditions has been evaluated. The [Cp*RuCI] complexes, such as Cp*RuCI(PPh(3))(2), Cp*RuCI(COD), and Cp*RuCI(NBD), were among the most effective catalysts. In the presence of catalytic Cp*RuCI(PPh(3))(2) or Cp*RuCI(COD), primary and secondary azides react with a broad range of terminal alkynes containing a range of functionalities selectively producing 1,5-disubstituted 1,2,3-triazoles; tertiary azides were significantly less reactive. Both complexes also promote the cycloaddition reactions of organic azides with internal alkynes, providing access to fully-substituted 1,2,3-triazoles. The ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) appears to proceed via oxidative coupling of the azide and alkyne reactants to give a six-membered ruthenacycle intermediate, in which the first new carbon-nitrogen bond is formed between the more electronegative carbon of the alkyne and the terminal, electrophilic nitrogen of the azide. This step is followed by reductive elimination, which forms the triazole product. DFT calculations support this mechanistic proposal and indicate that the reductive elimination step is rate-determining.