Quantification of the Interaction of SmI₂ with Substrates and Ligands

Abstract

The methodd eveloped and introduced here enables for the first time (to the authors' knowledge), aq uantitative assessment of the interaction of SmI 2 with substrates prior to the electron transfer stage. As ap roof of concept, equilibrium constants for some model substrates including carbonyl compounds and aromatic nucleia re reported here. In addition, the first equilibrium constants with some common ligands were also determined. The equilibrium constants range from approximately 0.07 m À1 for diisopropyl ketone to 2500 m À1 for hexamethylphosphoramide (HMPA). It is shown that the data acquiredb yt his method,w hich is based on the concept of shift reagents, can shed light on the most intimate detailso ft he reaction mechanism, and this methodi sauseful toolf or planning as ynthetic process.[a] Aand Ba re computational methods.Please see text.

Tools and techniques for solution‐phase structural understanding of SmI2–additive complexes

“…In a remarkable contribution to SmI 2 –additive chemistry, Hoz group developed an NMR‐based method to calculate the equilibrium constant for the SmI 2 –additives and SmI 2 –substrate interaction. [ 27 ] This methodology is based on the principle of a shift reagent, that is, shift in the NMR signal of ligand/substrate as a result of SmI 2 coordination (Scheme 4).…”

“…In other words, the obtained equilibrium constant represents the first coordination of ligand to the SmI 2 . [ 27 ]…”

“…The results also demonstrated that while replacing oxygen atom with nitrogen, the equilibrium constant increases confirming higher azaphilicity of SmI 2 . [ 27 ]…”

“…An interesting finding in this direction was equilibrium constant for ethylbenzene (1.14 M −1 ) was higher compared with p ‐chloroethylbenzene (0.73 M −1 ). [ 27 ] This suggests that SmI 2 forms a tighter complex with benzene ring compared with chlorine. This is a breakdown of the common notion that electron transfer to aromatic ring is completely outer sphere in nature, and the inner sphere nature increases when there is a heteroatom.…”

“… 1 H‐NMR chemical shift of methylene protons of p ‐chloroethylbenzene at different concentrations of SmI 2 (0–70 mM). Reproduced from ref., [ 27 ] with permission…”