The Chemical Structure, Dynamics and Mechanisms B Program supports Professor Robert A. Flowers of Lehigh University to carry out mechanistic studies on the chemistry of samarium diiodide (SmI2). SmI2 is an important reagent in organic synthesis due to its versatility in mediating numerous, fundamentally important reactions in organic synthesis including reductions, reductive couplings, and cascade reactions. One of the important features of SmI2 is that the addition of cosolvents or additives can be used to control the chemo- and diastereoselectivity of reactions. There are two scientific objectives of this work. The first objective is to carry out mechanistic studies that define the impact of the affinity of solvents, proton donors, and coordinating or chelating additives for Sm(II) reagents. The relationship between these variables and the reactivity of Sm(II) will be applied to the development of alternative approaches for the reduction of functional groups by SmI2 using readily available, inexpensive, and non-toxic additives. The second objective of this work will focus on mechanistic studies designed to examine known SmI2-based catalytic systems and employ the information gleaned from these studies to aid in the development of catalytic reactions employing SmI2 and other Sm(II)-based reductants.
The high degree of sophistication of many organic reactions that proceed through the transfer of electrons is based on our mechanistic understanding of anions, cations, radicals, and related radical ions. The ability of chemists to interconvert these intermediates through the use of metal-based oxidants and reductants has led to the development of reactions that utilize one or more reactive intermediates in bond-forming events to synthesize complex molecules of great societal importance. The most widely used single electron reductant is SmI2, but the roles of additives in these reactions are not well understood. The experiments carried out within the framework of this project are designed to provide a mechanistic understanding of Sm(II)-based chemistry and the role of additives that can be extrapolated and applied to a range of important and useful processes including the development of catalytic reactions. Studies utilizing this mechanism-centered approach are likely to provide longer-term benefits to the scientific community than the demonstration of a single synthetic application.
