Bridging Electrochemistry and Photoelectron Spectroscopy in the Context of Birch Reduction: Detachment Energies and Redox Potentials of Electron, Dielectron, and Benzene Radical Anion in Liquid Ammonia

TL;DR

This study characterizes key intermediates in Birch reduction by combining electrochemical and spectroscopic techniques, providing insights into electron binding energies and reaction mechanisms in liquid ammonia.

Contribution

It uniquely integrates cyclic voltammetry, photoelectron spectroscopy, and electronic structure calculations to analyze Birch reduction intermediates.

Findings

Quantified electron binding energies of intermediates

Connected electrochemical and spectroscopic data for Birch reduction

Provided mechanistic insights into electron transfer processes

Abstract

Birch reduction is a time-proven way to hydrogenate aromatic hydrocarbons (such as benzene), which relies on the reducing power of electrons released from alkali metals into liquid ammonia. We have succeeded to characterize the key intermediates of the Birch reduction process - the solvated electron and dielectron and the benzene radical anion - using cyclic voltammetry and photoelectron spectroscopy, aided by electronic structure calculations. In this way, we not only quantify the electron binding energies of these species, which are decisive for the mechanism of the reaction but also use Birch reduction as a case study to directly connect the two seemingly unrelated experimental techniques.