Two Competing Mechanisms for the Copper-Free Sonogashira Cross-Coupling Reaction

Autor:	Thomas Ljungdahl, Hans Emtenäs, Jerker Mårtensson, T.H Bennur, Andrea Dallas
Rok vydání:	2008
Předmět:	Inorganic Chemistry Reaction mechanism Nucleophile Chemistry Organic Chemistry Cationic polymerization Sonogashira coupling Amine gas treating Reaction intermediate Physical and Theoretical Chemistry Photochemistry Coupling reaction Catalysis
Zdroj:	Organometallics. 27:2490-2498
ISSN:	1520-6041 0276-7333
Popis:	The mechanism of the copper-free Sonogashira cross-coupling was investigated using a model reaction with differently para-substituted phenylacetylenes and 4-iodobenzotrifluoride as coupling partners and a Pd2(dba)3·CHCl3−AsPh3 catalyst system in methanol. A carbopalladation mechanism was ruled out through a series of experiments in which the equivalent of a carbopalladation reaction intermediate was synthesized by an alternate route, and its conversion to product was monitored. A Hammett correlation study revealed a possible mechanistic changeover when going from electron-rich to electron-poor alkynes in the model reaction. It is advocated that the reaction mechanism changes from a pathway involving a fast proton transfer from a slowly forming cationic Pd complex to a pathway involving a slow proton transfer from a neutral Pd complex on going from electron-rich to electron-poor alkynes. The amine base is believed to act as a base in both pathways and as a nucleophile promoting the formation of the cationi...
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_________::9706066a030ec9920b9f47e49ebb6b55 https://doi.org/10.1021/om800251s Zobrazit plný text záznamu