Rethinking the Sn2 Reaction to Achieve Catalysis
The Sn2 reaction is a fundamental transformation in organic chemistry that is usually described as the displacement of a leaving group from an alkyl group by a nucleophile. This formulation obscures the fact that in the reverse direction, the roles of the nucleophile and leaving group are interchanged, so every nucleophile is also a potential leaving group. The ability of a Lewis base to act as both a nucleophile and as a leaving group is encapsulated in the measurement of the rate of the (degenerate) reaction where the same group acts as both, a so-called self-exchange rate. Groups that have high self-exchange rates can potentially act as catalysts, as exemplified by the naturally occurring Vitamin B12-dependent methyltransferase enzymes.
We have recently measured unprecedentedly high Sn2 self-exchange rates for some synthetic cobalt complexes. This project will involve
- Measuring self-exchange rates and the stereospecificity of self-exchange reactions
- Documenting the ability of the cobalt complexes to serve as Sn2 catalysts
- Preparing new complexes to assess the effect of reaction thermodynamics on kinetics and catalysis
- Testing the ability of the cobalt complexes to perform enantioselective alkylations
The Brown group brings together a group of graduate and undergraduate students to study chemical reactivity. The overarching theme of our research is to understand unusual aspects of bonding and electronic structure and to explore how those bonding features translate to novel patterns of reactivity. In addition to the project described above, the other main emphasis of the lab is in preparing and studying high-valent terminal oxo and nitrido complexes of the late transition metals (especially iridium).