Microencapsulated Palladium Catalysts:Allylic Substitution and Coupling Using a Recoverable and Reusable Polymer-Supported Palladium Catalyst

摘要

While palladium catalysts find wide-spread utility in a variety of transformations in organic synthesis,they are expensive,air-sensitive,and cannot be recovered in many cases.Immobilized palladium catalysts have been expected to solve these problems,and several polymer-supported palladium catalysts have been developde for allylic substitution oligomerization ,decartion,Suzuki coupling an the Mizoroki -Heck reaction ,etc.In most of these cases,however,recovery and reuse of the polymer catalysts have not been satisfactory.Recetly,we developed novel polymer -supported catalysts,microencapsulated scandium trifluoromethanesulfonate(MCSc(OTf)_3) and osmium tertroxide(MCOs O_4).Our work has demonstrated a new method for immobilizing catalysts onto polymers based on physical envelopment by the polymers and on eleftronic interaction between the #pi# electrons of the benzene rings of the polystyrene-based polymers and vacant orbitals of the catalysts.We now apply this new technology to immobilizing palladium catalysts.Herein,we describe the use of microencapsulated triphenylphosphane palladium for allylic substitution and Suzuki coupling .In both cases,the catalysts were recovered quantitatively and reused.Moreover valuable information on the structure of microencapsulated catalysts was obtained.