Rational Reaction Promoter and Ligand Design in Synthesis

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Nontechnical: In this project, funded by the Chemical Catalysis program of the Chemistry Division, Professor Gerald B. Hammond, of the University of Louisville, is improving the efficiency of ionic reactions in chemical synthesis. Ionic reactions, involving by definition charged species, are the most common reactions used in chemical synthesis. Such synthesis plays a vital role in pharmaceuticals, materials, agrochemicals and many other related fields. The broader impacts of this project involve training postdoctoral fellows and graduate and undergraduate students, and enhancing the recruitment opportunities of Hispanic American students through symposia featuring high-profile Hispanic-American chemists, and scientific collaborations with Latin American faculty. The proposed work impacts the manufacturing industry broadly defined because it gives ready access to catalysts and promoters capable of streamlining chemical syntheses.Technical: Whether ions are separated or associated with each other depends on the polarity of the solvent. In low dielectric constant solvents, ions usually exist as ion pairs. The reactivity of a paired working ion is considered lower than the corresponding 'free' ion although there has been no systematic approach to understand, in quantitative or mathematical terms, the effect of ion pairing in ionic reactions. In most theoretical and experimental studies of ionic reactions, counterions are simply ignored. The hypothesis espoused in this project is that the transition state structure in an ionic reaction is bigger in size than the starting ion pair and is distorted by the counterion. The work to be carried out should lead to the design of reaction promoters and ligands that will reduce the hindrance effect of ion pairing, which, in turn, may lead to higher reactivity in ionic reactions. This research makes available broadly applicable reaction promoters, polymer-bound reaction promoters, and chiral reaction promoters, as well as chiral super strong Bronsted acids. In addition, bulky ligands are to be utilized in cationic gold catalysis and other cationic metal catalysis--with or without a reaction promoter--with the ultimate goal of ushering in a new generation of cationic metal catalyst with unprecedented reactivity at ppm level loadings under mild reaction conditions. Experimental investigations of ion pairing in typical reaction systems, and developing calculation methods to measure the distance between ions in an ion pair, as well as the size of ions, are performed using computational chemistry techniques by a collaborator, Professor Robert Paton, from Oxford University, England.