Azide-alkyne Huisgen cycloaddition: Difference between revisions

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== Ruthenium catalysis==

The [[ruthenium]]-catalysed 1,3-dipolar azide-alkyne cycloaddition ('''RuAAC''') gives the 1,5-triazole.

Unlike CuAAC in which only terminal alkynes reacted, in RuAAC both terminal and internal alkynes can participate in the reaction. This suggests that ruthenium [[acetylide]]sacetylides are not involved in the [[catalytic cycle]].

The proposed mechanism suggests that in the first step, the [[spectator ligand]]s undergo displacement reaction to produce an [[activated complex]] which is converted, viathrough [[oxidative coupling]] of an alkyne and an azide to the ruthenium containing metallocyle (Ruthenacycle). The new [[carbon-nitrogen bond|C-N bond]] is formed between the more electronegative and less sterically demanding carbon of the alkyne and the terminal nitrogen of the azide. The metallacycle intermediate then undergoes reductive elimination releasing the aromatic triazole product and regenerating the catalyst or the activated complex for further reaction cycles.

Cp^*RuCl(PPh₃)₂, Cp^*Ru(COD) and Cp^*[RuCl₄] are commonly used ruthenium catalysts. Catalysts containing cyclopentadienyl (Cp) group are also used. However, better results are observed with the pentamethylcyclopentadienyl(Cp^*) version. This may be due to the sterically demanding Cp^* group which facilitates the displacement of the spectator ligands.<ref>{{cite journal | authors = Li Zhang, Xinguo Chen, Peng Xue, Herman H. Y. Sun, Ian D. Williams, K. Barry Sharpless, Valery V. Fokin, and Guochen Jia; |lastauthoramp=yes | title = Ruthenium-Catalyzed Cycloaddition of Alkynes and Organic Azides | year = 2005| journal = [[J. Am. Chem. Soc.]] | volume = 127 | issue = 46 | pages = 15998–15999 | doi = 10.1021/ja054114s | pmid = 16287266}}</ref><ref>{{cite journal |author1=Brant C. Boren |author2=Sridhar Narayan |author3=Lars K. Rasmussen |author4=Li Zhang |author5=Haitao Zhao |author6=Zhenyang Lin |author7=Guochen Jia |author8=Valery V. Fokin | title = Ruthenium-Catalyzed Azide−Alkyne Cycloaddition: Scope and Mechanism | year = 2008| journal = [[J. Am. Chem. Soc.]] | volume = 130 | issue = 28 | pages = 8923–8930 | doi = 10.1021/ja0749993 | pmid = 18570425}}</ref>

[[ImageFile:RuAAC mechanism.png|center|450px|Mechanism for ruthenium-catalysed click chemistry]]

== Silver catalysis==