The Development and Application of Homogeneous and Heterogeneous Late Metal Complexes in Catalysis
In recent years, gold(I) complexes have seen increased use as catalysts for the activation of alkynes toward nucleophilic addition. Now, studies show that carbene–like intermediates are accessible, often depending on the substrates and catalyst ligands utilized. While metal carbenoid behavior for gold(I) has been proposed in other transformations, our research has expanded the reactivity of gold beyond simple electrophilic activation, based on evidence that gold can function as both a π–acid and as an electron donor. For instance, electron donation from gold d–orbitals can serve to facilitate the formation of gold carbenoid intermediates after initial cycloisomerization. The gold carbenoid species is then capable of undergoing subsequent reactivity to generate synthetically useful products that can also be further functionalized. Chapter 1 will discuss the development of new gold(I) carbenoid reactivity whereby an oxidation even results in oxygen atom transfer to the carbenoid center to generate carbonyl functional groups. The broad range of reactions for which this methodology can be applied will be discussed as will catalyst and ligand effects for the transformations.
During the course of our investigations into homogeneous gold catalysis, several relevant questions consistently arise. Among them are whether the catalyst can be recovered and recycled, what the cost is of the catalyst, and how load the catalyst loading can be. In order to address these issues, we initiated a research program focused on studying the translation of homogeneous catalytic processes to heterogeneous ones, all in the solution phase. In doing so, we could obtain catalytic activity with heterogeneous catalysts for reactions that were previously only obtained homogeneously. Chapter 2 details our efforts in pursuit of this goal and successes in developing oxidatively modified, electrophilic platinum nanoparticles that display activity for a range of π–bond activation/cyclization reactions. Our characterization studies for the designed nanoparticle system and examination of catalyst activity are presented, as are catalyst leaching investigations. Initial efforts into flow reactors and new dendrimer capping agents are also discussed. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis.