title: Association and Dissociation of Grignard Reagents RMgCl and Their Turbo Variant RMgCl⋅LiCl.
abstract: Grignard reagents RMgCl and their so-called turbo variant, the highly reactive RMgCl⋅LiCl, are of exceptional synthetic utility. Nevertheless, it is still not fully understood which species these compounds form in solution and, in particular, in which way LiCl exerts its reactivity-enhancing effect. A combination of electrospray-ionization mass spectrometry, electrical conductivity measurements, NMR spectroscopy (including diffusion-ordered spectroscopy), and quantum chemical calculations is used to analyze solutions of RMgCl (R=Me, Et, Bu, Hex, Oct, Dec, iPr, tBu, Ph) in tetrahydrofuran and other ethereal solvents in the absence and presence of stoichiometric amounts of LiCl. In tetrahydrofuran, RMgCl forms mononuclear species, which are converted into trinuclear anions as a result of the concentration increase experienced during the electrospray process. These trinuclear anions are theoretically predicted to adopt open cubic geometries, which remarkably resemble structural motifs previously found in the solid state. The molecular constituents of RMgCl and RMgCl⋅LiCl are interrelated via Schlenk equilibria and fast intermolecular exchange processes. A small portion of the Grignard reagent also forms anionic ate complexes in solution. The abundance of these more electron-rich and hence supposedly more nucleophilic ate complexes strongly increases upon the addition of LiCl, thus rationalizing its beneficial effect on the reactivity of Grignard reagents.
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schnegelsberg
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, 37077, Göttingen, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Bachmann
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany.
authors.forename: Marlene
authors.initials: M
authors.lastname: Kolter
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Auth
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: John
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, 37077, Göttingen, Germany.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Stalke
authors.affiliation: Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077, Göttingen, Germany. konrad.koszinowski@chemie.uni-goettingen.de.
authors.forename: Konrad
authors.initials: K
authors.lastname: Koszinowski
keywords: Grignard reagents; NMR spectroscopy; mass spectrometry; reactive intermediates; salt effect