Advances and challenges in user-friendly alkyne metathesis catalysts

Multidentate ligands have attracted significant attention in the design and synthesis of highly active alkyne metathesis (AM) catalysts. The functional group compatibility of AM catalysts has been improved dramatically, with many conventionally challenging substrates containing cyano, aldehyde, nitro, carboxylic acid, and/or terminal alkyne groups becoming metathesis active. Very recent progress in catalyst development, including in situ generated Mo(VI) catalysts consisting of simple multidentate tris(2-hydroxyphenyl)methane ligands and well-defined Re(V) carbyne complexes, has enabled AM to proceed under open air conditions. Catalysts with different activities are needed for different metathesis reactions. Usually catalysts with relatively lower activity are suitable for polymer synthesis, particularly through living polymerization, while highly active catalysts are desired for the synthesis of discrete molecular architectures. Encapsulation, dormant precursors, and grafting to solid supports are three demonstrated strategies that can improve the user-friendliness and practical applicability of AM catalysts. Alkyne metathesis (AM), the cousin of the ‘noble’ alkene metathesis, has attracted rapidly growing attention within the past 20 years and has been widely used in the synthesis of natural products, functional polymers, and shape-persistent molecular architectures. Given some excellent reviews in recent years, this article will not provide a comprehensive review of the catalyst development and the wide applications of AM, but rather will focus on the rational design of the catalysts, substrate structures, and reaction conditions that meet the requirements of certain metathesis pathways (e.g., cyclooligomerization, polymerization, self-correction) and will make the catalytic systems more user-friendly and practically useful (e.g., operating in air and with long lifetimes and broad substrate scope). Alkyne metathesis (AM), the cousin of the ‘noble’ alkene metathesis, has attracted rapidly growing attention within the past 20 years and has been widely used in the synthesis of natural products, functional polymers, and shape-persistent molecular architectures. Given some excellent reviews in recent years, this article will not provide a comprehensive review of the catalyst development and the wide applications of AM, but rather will focus on the rational design of the catalysts, substrate structures, and reaction conditions that meet the requirements of certain metathesis pathways (e.g., cyclooligomerization, polymerization, self-correction) and will make the catalytic systems more user-friendly and practically useful (e.g., operating in air and with long lifetimes and broad substrate scope). an electrically neutral carbon-active intermediate with three free electrons. a reaction involving reversible breaking and reformation of carbon–carbon triple bonds in alkynes. a reaction in which two compounds exchange components with each other to form another two compounds with swapped components. ring-opening reaction of ring-strained alkynes to form alkyne polymer.