Contrasting Effect of Additives on Photoinduced Reactions of SmI₂

Abstract

The work described herein compares the effect of additives (HMPA, methanol, ethylene glycol, pinacol, N-methylethanolamine) on thermal and photochemical reactions of samarium diiodide (SmI 2 ). In thermalr eactions,a dditives that coordinate to SmI 2 induce as ignificant increase in reaction rate. In photochemicalr eactions,t he presence of an electronegative atom with ah ighly localizednegative charge on the substrate leads to ar ate deceleration. In order to benefit from the columbic interaction with the positivelyc harged samarium cation, these substrates react preferentially by an inner sphere reduction mechanism. The addition of ligands preventst his close interactionc ausingr ate retardation. Furthermore, studies demonstrate that excited state quenching of Sm II by ethylene glycol and other additivesi ndicate that it is unlikely to be the major cause for the observed rate retardation.T his effect provides as imple diagnostic tool to distinguish between an inner and an outer sphere reduction mechanism. Results and DiscussionTo study this system,a nthracene, trans-stilbene, benzyl chloride, halobenzenes, cyclohexanone and 3-methyl-2-butanone were chosen as substrates since they are representative of the [a] Dr.

Properties of Amine-Containing Ligands That Are Necessary for Visible-Light-Promoted Catalysis with Divalent Europium

“… The complex has an excited-state electrochemical potential of −3.2 V versus normal hydrogen electrode (NHE). This potential is one of the most negatively reported excited-state potentials for metal-based photoredox catalysis and is more negative than the common reducing agent SmI 2 in the presence of hexamethylphosphoramide. , The essential properties of 1 that are required for visible-light-promoted photocatalysis with Eu II are unclear, and to design new ligands that promote photoredox catalysis with Eu II , the effects of the ligand properties must be elucidated. Because the reported catalyst based on Eu II involved octaaza ligand 1 , we hypothesized that studying the influence of a set of amine-containing ligands on the electrochemical and photophysical properties of Eu II would reveal the ligand attributes necessary to promote reactivity in visible-light-promoted reductions.…”

Samarium Iodide Showcase: Unraveling the Mechanistic Puzzle

“…Consequently, an intensive coordination of ligands to SmI 2 may prevent the association of the Sm 3+ with an electronegative atom on the radical anion and force an outer sphere electron transfer mechanism in cases where an inner sphere is preferred. This is nicely exemplified in the photocatalyzed reactions of benzyl chloride and anthracene with EG as an additive . Increasing the concentration of the ligand reduces the rate for benzyl chloride but enhances the rate for anthracene (cf.…”

“…Pseudo-first-order rate constants for the photoinduced reaction of benzyl chloride as a function of the concentration of ethylene glycol. Reproduced with permission from ref . Copyright 2019 Wiley-VCH.…”

“…This is nicely exemplified in the photocatalyzed reactions of benzyl chloride and anthracene with EG as an additive. 34 Increasing the concentration of the ligand reduces the rate for benzyl chloride but enhances the rate for anthracene (cf. Figures 14 and 15)…”

Light in SmI2‐mediated chemistry: Synthetic applications and mechanistic studies

“…26 The photoinduced reduction of substrates by SmI 2 was employed as a tool to distinguish the "outer sphere" and "inner sphere" nature of electron transfer. 31 The rate of reduction of a series of substrates, including anthracene, cyclohexanone, benzyl chloride, and chlorobenzene, was monitored while varying the concentration of ethylene glycol (EG). The results showed two distinct patterns: For substrates where electron transfer is mostly outer sphere, an increase in [EG] led to an increase in the rate of reduction.…”