Synthesis and catalytic evaluation in the Heck reaction of deposited palladium catalysts immobilized via amide linkers and their molecular analogues
Abstract
A series of deposited palladium catalysts was prepared by amidation of 3-aminopropylated silica gel with donor-functionalized acetic acids followed by treatment with palladium(II) acetate. The resulting materials containing YCH2CONH(CH2)(3)Si groups at the surface, where Y= SMe, NMe2, and PPh2, as well as the corresponding catalysts generated in situ from the analogous molecular donors YCH2CONH(CH2)(2)Me and palladium(II) acetate were evaluated in the Heck reaction of n-butyl acrylate with bromobenzene to give n-butyl cinnamate.
The heterogenized catalysts afforded consistently better yields of the coupling product than their respective molecular counterparts with the best results being achieved with the catalyst obtained from the amidoamine-functionalized support (Y =NMe2). Additional tests revealed that the deposited catalysts serve as a source of active metal for the reaction occurring in the liquid phase and that the yield of the coupling product is controlled by the amount of the leached-out metal.