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-Bu 2 Mg • LiCl • 4 thf] with two tert-butyl anions at the magnesium center and incorporated lithium chloride.

Morphological Plasticity of LiCl Clusters Interacting with Grignard Reagent in Tetrahydrofuran

“…Attempts to determine the nature of turbo Grignard reagents suffer from the fact that experimental characterization, by crystallization or spectroscopic methods, requires experimental conditions different from those at which reactions occur. Thus, for decades, no neutral Li:Mg moiety was reported in either the gas phase or solid state, but this was not conclusive on their existence in solution. , Indeed, very recently tBu 2 MgClLi­(THF) 4 was isolated and characterized by X-ray crystallography, and its presence in solution was assessed by NMR spectroscopy, its monomeric form possibly being promoted by the bulky tBu groups …”

“…These charged moieties could interact with the organomagnesium compounds present in solution, yielding other species of diverse reactivity. The LiCl-assisted enrichment of dialkylmagnesium confirms the original proposal by Knochel about its presence in solution, and it is also in line with its recent characterization as tBu 2 MgClLi­(THF) 4 in the solid state . This work urges further investigation on the fragmentation of Li:Mg:X clusters into neutral and ionic compounds as a function of R, halides, and solvent and on the consequences for turbo Grignard reagents.…”