3 years ago

SmI2(H2O)n Reduction of Electron Rich Enamines by Proton-Coupled Electron Transfer

SmI2(H2O)n Reduction of Electron Rich Enamines by Proton-Coupled Electron Transfer
Scott S. Kolmar, James M. Mayer
Samarium diiodide in the presence of water and THF (SmI2(H2O)n) has in recent years become a versatile and useful reagent, mainly for reducing carbonyl-type substrates. This work reports the reduction of several enamines by SmI2(H2O)n. Mechanistic experiments implicate a concerted proton-coupled electron transfer (PCET) pathway, based on various pieces of evidence against initial outer-sphere electron transfer, proton transfer, or substrate coordination. A thermochemical analysis indicates that the C–H bond formed in the rate-determining step has a bond dissociation free energy (BDFE) of ∼32 kcal mol–1. The O–H BDFE of the samarium aquo ion is estimated to be 26 kcal mol–1, which is among the weakest known X–H bonds of stable reagents. Thus, SmI2(H2O)n should be able to form very weak C–H bonds. The reduction of these highly electron rich substrates by SmI2(H2O)n shows that this reagent is a very strong hydrogen atom donor as well as an outer-sphere reductant.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b03667

DOI: 10.1021/jacs.7b03667

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