Comprehensive Study of the Enhanced Reactivity of Turbo-Grignard Reagents

Abstract

Since its introduction in 2004, Knochel's so called Turbo-Grignard reagents revolutionized the usage of Grignard reagents. Through the simple addition of LiCl to a magnesium alkyl an outstanding increase in reactivity can be achieved. Though the exact composition of the reactive species remained mysterious, the reactive mixture itself is readily used not only in synthesis but also found its way into more distant fields like material science. To unravel this mystery, we combined single-crystal X-ray diffraction with in-solution NMR-spectroscopy and closed our investigations with quantum chemical calculations. Using such a variety of methods, we have gained insight into and an explanation for the extraordinary reactivity of this extremely convenient reagent by determining the structure of the first bimetallic reactive species [t-Bu₂ Mg ⋅ LiCl ⋅ 4 thf] with two tert-butyl anions at the magnesium center and incorporated lithium chloride.

Keywords: Grignard Reaction; Metal-Halogen Exchange; Turbo-Grignard; X-Ray Diffraction.