Science of Synthesis

Pitaval, A.; Echavarren, A. M., Science of Synthesis: Cross Coupling and Heck-Type Reactions, (2013) 1, 535.

The use of heterogeneous catalysts in cross-coupling reactions, including Stille couplings, has been reported.[‌179‌–‌184‌] Performing C—C bond-forming reactions in aqueous media avoids the use of expensive, toxic, and/or flammable organic solvents. With consideration of both of these modifications, a ligand-free Stille reaction, using palladium/calcium carbonate as a catalyst reservoir, has been applied in the coupling of aryl halides with tributyl(phenyl)stannane in ethanol/water (‌Scheme 10‌);[‌185‌] the addition of potassium carbonate is also required. Turnover numbers are between 60 and 98. The method is also successful for aryl chloride electrophiles. The solid catalyst can be separated from the ethanol/water solution by centrifugation and decantation, and recycled. After extracting the product from the ethanol/water solution, the ethanol/water solution can be reused twice, giving good yields each time, which confirms the presence of a soluble palladium(0)/palladium(II) species as the true catalyst.

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References