Preparation of Samarium(II) Iodide: Quantitative Evaluation of the Effect of Water, Oxygen, and Peroxide Content, Preparative Methods, and the Activation of Samarium Metal

Samarium­(II) iodide (SmI₂) is one of the most important reducing agents in organic synthesis. Synthetic chemistry promoted by SmI₂ depends on the efficient and reliable preparation of the reagent. Unfortunately, users can experience difficulties preparing the reagent, and this has prevented realization of the full synthetic potential of SmI₂. To provide synthetic chemists with general and reliable methods for the preparation of SmI₂, a systematic evaluation of the factors involved in its synthesis has been carried out. Our studies confirm that SmI₂ is a user-friendly reagent. Factors such as water, oxygen, and peroxide content in THF have little influence on the synthesis of SmI₂. In addition, the use of specialized glovebox equipment or Schlenk techniques is not required for the preparation of SmI₂. However, our studies suggest that the quality of samarium metal is an important factor and that the use of low quality metal is the main cause of failed preparations of the reagent. Accordingly, we report a straightforward method for activation of “inactive” samarium metal and demonstrate the broad utility of this protocol through the electron transfer reductions of a range of substrates using SmI₂ prepared from otherwise “inactive” metal. An investigation into the stability of SmI₂ solutions and an evaluation of commercially available solutions of the reagent is also reported.