Homogeneously-Catalyzed Coupling Reactions in Switchable Solvents

Abstract

Due to the increasing environmental impact of society, it is imperative that current industrial processes be modified and new industrial processes be implemented in order to reduce environmental harm. However, these new or modified processes must be more energy-efficient, materials-efficient, and cost-effective so that they are more economically beneficial than the other processes. The described research was inspired by these two ideas and is comprised of two projects, both focused on the creation of recyclable, CO2-switchable methods of separating organic products, inorganic byproduct and catalyst. For the first part of the project, Suzuki-Miyaura cross-couplings were tested in switchable water, concentrating on the activation of aryl chlorides and product separation techniques. Switchable water, which is an aqueous solution of an amine, was used as solvent with the amine functioning as the base for the palladium-catalyzed Suzuki-Miyaura cross-coupling of activated aryl chlorides with phenyl boronic acid, using TPPTS (a water-soluble phosphine ligand). The use of Schlenk techniques resulted in conversion of 99% and isolated yields of 87% with the absence of homocoupling. For the second part of the project, the development of an easily prepared CO2-switchable polymeric ligand is described. The polymeric ligand was used in the Suzuki-Miyaura cross-coupling reaction for the synthesis of a biaryl product using 4-iodobenzaldehyde and phenylboronic acid pinacol ester in water. With the help of this switchable polymeric ligand, organic product, inorganic byproduct, and catalyst were separated into three fractions. A catalyst recycling system was developed for the Suzuki-Miyaura cross-coupling reaction. The catalyst was able to be recovered and reused, albeit with lower activity.