Reduction of substrates by SmI2-water, and glycols is a complex process. These proton donors have a high affinity for Sm(II) and compete with substrate for coordination to the metal center. To study the process without the complication of substrate coordination, anthracene was chosen as a model substrate. Stopped-flow rate studies on the reduction of anthracene showed that as the concentrations of water and ethylene glycol were increased, an increase in reaction rate was observed as well as a change in order of proton donor. Deuterium kinetic isotope studies provided an average kH/kD of 1.75 for water and 1.8 for ethylene glycol over the entire concentration range. Activation parameters revealed a large negative ΔSŦ and a very small ΔHŦ showing a highly-ordered early transition state consistent with a primary isotope effect. Addition of acidic, non-coordinating proton donors slightly decreased the rate of reduction indicating that protonation does not arise from the bulk, but from two proton donors directly involved in the rate-limiting protonation.

Elucidating the role of SmI2-water and glycol in reductions: Mechanistic studies of anthracene reduction

249th National Meeting (2015)

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