Task-Dependent Coordination Levels of SmI₂

Abstract

Ligation plays a multifaceted role in the chemistry of SmI2. Depending on the ligand, two of its major effects are increasing the reduction potential of SmI2, and in the case of a ligand, which is also a proton donor, it may also enhance the reaction by protonation of the radical anion generated in the preceding step. It turns out that the number of ligand molecules that are needed to maximize the reduction potential of SmI2 is significantly smaller than the number of ligand molecules needed for a maximal enhancement of the protonation rate. In addition to the economical use of the ligand, this information can also be utilized as a diagnostic tool for the reaction mechanism in differentiating between single and multistep processes. The possible pitfalls in applying this diagnostic tool to PCET and cyclization reactions are discussed.

Samarium Iodide Showcase: Unraveling the Mechanistic Puzzle

“…Figure 8 shows the effect of EG on the reduction potential of SmI 2 and on the rate constants for the benzyl chloride reaction. 26 As can be seen, the two graphs coincide. However, with anthracene and cyclohexanone, the graphs are separate, and the one for cyclohexanone is closer to the reduction potential curve than the one for anthracene (Figure 9).…”

“…Figure shows the effect of EG on the reduction potential of SmI 2 and on the rate constants for the benzyl chloride reaction . As can be seen, the two graphs coincide.…”

Contrasting Effect of Additives on Photoinduced Reactions of SmI2

“…[6] Proton donors and Lewis bases that coordinate to SmI 2 may affect reactions through severald ifferentp athways. The most common pathways are a) increasing the reduction potentialo f SmI 2 ; [4b,c] b) protonation of ar adical anion generated from an initial electront ransfer step [7] c) promoting proton-coupled electron transfer in which transfer of electron and proton occur in as ingle kinetic step [8] and d) coordinationt ot he inner sphereo fS mI 2 creating as terically encumbered reductant.T he first three effects usually contributet oar ate increasew hereas the fourth is less predictable regarding the rate of reduction but is well recognizedf or its ability to change the course of the reaction, predominantly by enhancing the stereochemical outcome of reactions. [4f, 9] Since SmI 2 has as tronga bsorption in the visible range, light can be used to accelerate several SmI 2 mediated reactions.…”