Three phase microemulsion/sol-gel system for aqueous C-C coupling of hydrophobic substrates

Heck, Stille, Suzuki and three-component coupling reactions with hydrophobic substrates have been carried out in water. The substrates are initially transformed by a general procedure into a microemulsion, which consists of nearly 90% water with the aid of sodium dodecyl sulfate and either PrOH or BuOH. The surfactant carries the molecules of the substrates to Pd(OAc)₂ entrapped within a hydrophobicitized silica sol-gel matrix where the coupling between the substrates is assumed to take place. The products are then returned by the surfactant into the microemulsion from which it can be released. The immobilized palladium catalyst is leach proof and recyclable. It can be used in various coupling processes at least six times without loss of activity. Experiments with D₂O have revealed that the water does not take part in the coupling process, but it has an effect on the pore size of the sol-gel matrix, which hosts the palladium catalyst.