Design and development of novel organoselenide-based transition metal catalysts and their utility in carbon-carbon and carbon-heteroatom bond formation reactions

Transitions metal catalyzed coupling reactions are of the most powerful tools for carbon-carbon and carbon-heteroatom bond formation in organic synthesis. The Heck reaction is one of the most widely used reactions in organic synthesis due to its unique use of various organic halides to undergo oxidation addition to palladium-based catalysts. This successful reaction can lead to the construction of a C-C bond at an unfunctionalized olefinic carbon in a single transformation employing a wide variety of aryl and vinyl halide substrates. Other coupling reactions, such as Suzuki coupling, have become widely used over the past decade in an assortment of biologically active compound synthesis. The conventional ligands used to stabilize the Pd catalysts for both the Heck reaction and the Suzuki coupling, include those that contain phosphorous, sulfur, nitrogen, phosphine, and oxygen atoms, demonstrate the need of further development due to high catalyst cost, high catalyst loading, and difficulty of handling as well as use of additives. In this research project, a number of novel organoselenide-based ligands were synthesized. They were subsequently used to prepare a variety of palladium catalysts. Three different types of palladium catalysts---namely, monoligated, palladacycles, and pincer types---were synthesized, and their roles in a variety of coupling reactions were examined. The results of this work show that the novel organoselenide-ligated palladium catalysts exhibit high activity in carbon-carbon forming reactions such as the Heck and the Suzuki couplings. In addition, a systematic study on the ligand-free Heck reaction established that the commercially readily available Pd(OAc)2 could be used as a highly reactive catalyst for the coupling of various aryl iodides as well as less reactive aryl bromides.