RUI: Origin of the Unusual Electronic Effects on Alkyne Migratory Insertion During First-Row Transition-Metal-Catalyzed Reactions

Samford University, Birmingham AL

Investigators

Abstract

With support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division, and the Established Program to Stimulate Competitive Research (EPSCoR), Dale Wilger of the Department of Chemistry at Samford University is systematically evaluating the mechanism for alkyne migratory insertion with first-row transition metal catalysts. Despite being intimately involved in the mechanism of reactions for the synthesis of drug molecules, plastics, and other commodity chemicals, alkyne migratory insertion is a an incompletely understood process, especially for first-row transition metal catalysts. The importance of first-row transition metal catalysts has grown rapidly in recent decades. Even though second- and third-row transition metal catalysts are critical to our civilization, they are generally scarce and thus present serious sustainability and cost issues. First-row transition metals hold promise as they are much more earth abundant and thus more sustainable and economical sources of catalysts. For reaction development to continue with first-row transitions metals, the fundamental mechanisms that govern their chemical behavior need to be properly defined. By studying a series of carefully designed Ni- and Co-catalyzed reactions, Dr. Wilger and his team will investigate the principles that control alkyne migratory insertion. The results of these studies have the potential to facilitate the development of first-row transition metal catalysts. This current project aims to fully define the mechanisms that control alkyne migratory insertion regioselectivity with first-row transition metals. Alkyne migratory insertion is a common elementary process in transition-metal-catalyzed reactions. However, the factors that govern the success and selectivity of these reactions are not well established, especially for first-row transition metals. For example, determining whether a particular alkyne migratory insertion will be kinetically accessible and/or regioselective is generally only possible through direct experimentation. In a recent study, alkyne migratory insertion selectivity in a Ni-catalyzed indenone synthesis was found to depend on both the steric properties of the alkyne and the electronic parameters of the aryl donor, a phenomenon which had not been observed for any previous transition metal-catalyzed reaction. If successful, this project will define the driving force for the observed regioselectivity effects, determine regioselectivity in related chemical transformations, and determine whether these selectivity effects are observed with other first-row transition metals. This information would greatly facilitate our understanding and design of first-row transition metal-catalyzed reactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.