Key Role of Water in Copper‐ and Base‐free Sonogashira Coupling in Ethanol with [{Pd(µ‐OH)Cl(IPr)}2] as a Highly Effective Precatalyst
Aryl bromides and 4-chlorotoluene as an example aryl chloride in the presence of N-heterocyclic carbene (NHC) palladium hydroxo dimers of the type [{Pd(µ-OH)Cl(NHC)}2] (where NHC = IPr, SIPr, IMes, SIMes) undergo an efficient and selective Sonogashira cross-coupling with (hetero)arylacetylenes. The procedure allows the high-throughput and selective synthesis of a broad spectrum of 1,2-diarylacetylenes using 10 ppm of [{Pd(OH)Cl(IPr)}2] as precatalyst. For the coupling of 4-chlorotoluene with phenylacetylene, TON = 560000 was achieved. Hydrogen chloride was observed as a product of the Sonogashira cross-coupling reaction. The formation of the active Pd(0) from the Pd(II) complex was found to proceed via ethanol oxidation. Mechanistic studies showed that water plays a key role in the reaction.
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![Key Role of Water in Copper‐ and Base‐free Sonogashira Coupling in Ethanol with [{Pd(µ‐OH)Cl(IPr)}2] as a Highly Effective Precatalyst](/_next/image?url=https%3A%2F%2Fcdn.gdch.de%2Fprod%2Fnadc20264158444_fig_0001_a_36fd5c002c.png&w=256&q=75)
![Key Role of Water in Copper‐ and Base‐free Sonogashira Coupling in Ethanol with [{Pd(µ‐OH)Cl(IPr)}2] as a Highly Effective Precatalyst](/_next/image?url=https%3A%2F%2Fcdn.gdch.de%2Fprod%2Fnadc20264158499_fig_0001_a_8463b1bf14.png&w=256&q=75)
![Key Role of Water in Copper‐ and Base‐free Sonogashira Coupling in Ethanol with [{Pd(µ‐OH)Cl(IPr)}2] as a Highly Effective Precatalyst](/_next/image?url=https%3A%2F%2Fcdn.gdch.de%2Fprod%2Fnadc20264158504_gra_0001_a_6653df00f8.png&w=256&q=75)
