Forcing a cis-product by matrix imprinting: Heck reaction catalyzed by palladium acetate entrapped within cis-imprinted sol-gel derived silicates

While the Heck coupling of aryl bromides with styrenes by palladium acetate entrapped within octylated silica sol-gel forms almost entirely trans-stilbenes, the catalysis by the palladium compound within the cis-pre-imprinted support gives stilbenes that are substantially enriched by cis-oriented isomers. Although the ceramic support is completely freed from the imprint prior to the coupling process, cis-stilbenes are formed with similar selectivities upon recycling of the catalyst systems for at least four consecutive runs.