Effect of Pd0/SiO2 on the catalysis of leached soluble Pd during the Heck reaction
The catalytic behaviour ofsoluble Pd leached fromconventionally prepared Pd0/SiO2 in the Heck coupling ofbromobenzene and styrene in the presence of NaOAc hasbeen studied. The catalytic activity of soluble Pd is inhibited inthe presence of the supported Pd particles although it is veryhigh in the absence of the supported Pd particles. Similar Pdleaching occurs irrespectively of whether the reactionsubstrates are present, resulting in similar homogeneouscatalytic activities. The results suggest that the Pd leachingdoes not rely on the action between an aryl halide andheterogeneous Pd and that the catalysis takes place viasoluble molecular Pd simply leached from the supported Pdparticles instead of the supported Pd particles or derivedsoluble Pd clusters to which oxidative addition ofbromobenzene is carried out to give a soluble PdIIintermediate.