Carbamoyl imidazolium salts in organic synthesis and organometallic chemistry

This thesis is a summary of research conducted since September 1998 in the laboratories of Professor Robert A. Batey at the University of Toronto. The manuscript is divided into two chapters. Chapter 1 describes the synthetic application of carbamoyl imidazolium salts. A wide variety of carbamoyl imidazolium salts and thiocarbamoyl imidazolium salts were synthesized efficiently through a two-step sequence. Most of the salts are stable crystalline materials that can be stored for extended periods. Polymer-supported strategies and liquid-liquid extractions have been applied successfully for the generation of unsymmetrical tri- and tetrasubstituted urea libraries. Similarly, reactions of thiocarbamoyl imidazolium salts with primary or secondary amines resulted in the formation of thioureas. In addition, reaction of the salts with soft carbon nucleophiles successfully generated beta-dicarbonyl amides.;Chapter 2 describes the development and application of new palladium N-heterocyclic carbene complexes. Carbamoyl-substituted N-heterocyclic carbene complexes of palladium(II) were synthesized readily from carbamoyl imidazolium salts and palladium acetate. As a demonstration of the catalytic activity of these carbene complexes, Suzuki-Miyaura cross-coupling reactions were investigated systematically and optimized for the effect of bases, solvents, additives, co-solvents and ligands. Under the optimized reaction conditions, Suzuki cross-coupling reactions of a wide array of aryl halides were affected under mild conditions and with turnover numbers as high as 580,000. The carbamoyl-substituted palladium carbene complexes efficiently promoted Sonogashira couplings under mild conditions constituting the first successful example of the application of an N-heterocyclic carbene complex in Sonogashira reaction. Cesium carbonate was found to be an effective base for the coupling of aryl bromides for the first time. Although not as effective as Suzuki-Miyaura and Sonogashira cross-coupling reactions, the complexes also catalyzed Heck couplings of different aryl iodides and activated aryl bromides with alkenes. Finally, the synthesis of a polymer-supported N-heterocyclic carbene complex of palladium is described, and shown to catalyze Sonogashira cross-coupling reactions.