Palladium-Catalyzed Reactions of Butadiene and Isoprene

Abstract

Publisher Summary This chapter focuses on the reactions of butadiene and isoprene in the presence of palladium catalysts, also related reactions catalyzed by nickel complexes are considered for comparison. Unlike nickel catalysts, palladium catalysts undergo neither cyclodimerization nor cyclotrimerization to form 1,5-cyclooctadiene (COD) or 1,5,9-cyclododecatriene (CDT). The chapter highlights that a mixture of divinylcyclobutanes was obtained from butadiene using palladium salts with non-complexing anions such as perchlorate and boron tetrafluoride. This is a big difference between the catalyses of palladium and nickel. There are two main types of reactions of conjugated dienes catalyzed by palladium complexes. The first type is the linear dimerization to form 1,3,7-octatriene in the absence of a nucleophile. The most characteristic and useful reaction is the dimerization with incorporation of certain nucleophiles. The second characteristic reaction catalyzed by palladium catalysts is cocyclization of butadiene with the C=O bonds of aldehydes and the C=N bonds of isocyanates and Schiff bases to form six-membered heterocyclic compounds (19) with two vinyl groups, as expressed by the following general scheme. These cocyclization reactions of butadiene are possible only with palladium catalysts.