Catalytic Investigations of Rhodium Acetate Derivatives to Develop Sturdier Insecticides Authors: Alexandria Marshall, Alain Beauparlant, Cassandra Eagle* Department of Chemistry, College of Arts and Sciences East Tennessee State University Johnson City, TN Permethrins are a class of naturally occurring, low-toxicity insecticides that are extracted from the chrysanthemum flower. This class of insecticides is primarily utilized for the treatment of head lice for humans and flea and tick treatment for pets. These naturally occurring permethrins have a low Lethal Dose for 50% (LD50) of the bug population and a high LD50 for mammalian species. Unfortunately, permethrins are sensitive to heat and light, which precludes their use in industries such as the Christmas tree industry and other outside sources of bugs. Pyrethroids, on the other hand, are lab-synthesized insecticides that have the same biological activity as permethrins but are light and heat stable. Rhodium acetate is a catalyst that is used during the synthesis of pyrethroids. This means rhodium acetate is a chemical that speeds up the rate of the reaction without getting consumed. The goal of this research is to understand the mode of action of rhodium acetate so that we can develop sturdier derivatives of permethrin insecticides that can be used in a wider variety of applications. Rhodium acetate catalyzes the most difficult step in the synthesis of pyrethroids, the formation of a cyclopropane ring where there are two bulky groups on the same side of the ring. The catalytically active species, a rhodium (II) acetate carbene species, where the carbene is created from ethyl diazoacetate, is, unfortunately, too unstable and short-lived to characterize thoroughly. We have synthesized a more stable model of the catalyst using nitrile and iso-nitrile adducts of the active site and have been able to study it with extreme precision using X-ray crystallography. The derivative we have synthesized is Rh2(OAc)4.2X, where OAc is the acetate group (the same active ingredient in household vinegar) and X is benzonitrile, NC-C6H5. This nitrile derivative is similar to a carbene in that they both have a lone pair of electrons capable of serving as a Lewis base to initiate sigma bonding with the dirhodium core. Another similarity they share is that both species have empty orbitals capable of accepting electron density to form pi-backbonds. The derivative was synthesized by using 10-30 mg of Rh2(OAc)4 in approximately 10 mL of ethanol. 1-200 equivalents of the benzonitrile are dissolved in ethanol in a separate container. Then, the Rh2(OAc)4 in ethanol and benzonitrile in ethanol were mixed together and kept in a container covered with a tissue to prevent dust from entering. The slow evaporation of the ethanol solvent results in high-quality crystals that are suitable for single crystal X-ray crystallography. The results from X-ray crystallography have provided us important information regarding the rhodium-rhodium bond distance, the rhodium-nitrogen bond distance, the nitrogen-carbon bond distance, and the rhodium-nitrogen-carbon bond angle. This data will poise us to determine the steric and electronic parameters of the cavity used for carbene coordination. The next steps of this project will be to apply these findings to actual carbene chemistry reactions to verify that the parameters are correct. Thus, it will reveal exactly what is necessary for a particular reaction to take place in terms of reactants.