Mechanistic Studies of Proton‐Donor Coordination to Samarium Diiodide

Abstract

Three's a crowd: Initial coordination of diethylene glycol to SmI2 liberates THF or iodide, thus providing open coordination sites for substrates and enhancing reactivity. Concentrations of diethylene glycol that lead to coordinative saturation of SmI2 (see structure) reduce its reactivity. Replacement of a hydroxy proton with a methyl group decreases the affinity of the chelate for SmI2, resulting in a decrease in the reactivity of the complex.

Aza versus Oxophilicity of SmI2: A Break of a Paradigm

“…The enthalpy of complexation for water and Et 3 N measured through ITC experiments was found to be comparable (−2.5 kcal mol −1 for water and −3.3 kcal mol −1 for Et 3 N). It was shown previously that introduction of alkyl group one oxygen has significant deleterious impact on the coordinating ability . We have also seen similar phenomenon when a methyl group was added on the nitrogen of ethanolamine (Figure ).…”

Mechanistic Studies on the Roles of Cosolvents and Additives in Samarium(II)-Based Reductions

“…These data support a mechanism in which the driving force for the increased reactivity of SmI 2 upon the addition of the coordinating proton donors is due to solvent or iodide displacement, similar to that observed with the addition of HMPA to SmI 2 . 51,67 With the mechanistic data on proton donors in hand, it is instructive to consider the observations described herein in the context of previous findings reported in the literature. One of the striking features of this work is the observation that water has an unusually high affinity for SmI 2 and competes with THF for coordination at very low concentrations compared with the bulk solvent.…”

Reversed Electron Apportionment in Mesolytic Cleavage: The Reduction of Benzyl Halides by SmI2

“…In most of the papers reporting the reaction of SmI 2 with benzyl halides, the benzylic system was used as a model or a vehicle to explore the landscape of SmI 2 capabilities. A number of examples of these are the lifetime of excited SmI 2 ,6 the issue of inner sphere versus outer sphere electron transfer,7 as a mechanistic probe for the reactions of SmI 2 –water,8 the effect of crown ethers on SmI 2 reactions,9 the effect of water,10 glyme,11 hexamethylphosphoramide (HMPA)12 and so on.…”