Solution Structure of Turbo‐Hauser Base TMPMgCl⋅LiCl in [D₈]THF

Abstract

What is the most significant result of this study? The most comprehensive three dimensional structural information we currently can have from molecules stem from X-ray diffraction of the solid state. We need to have this information because we have to identify reactive species which might have to be modified to further foster their chemical performance. Turbo-Hauser bases are such outstanding performers, as they show enhanced reactivity while being gentle to many other present functional groups at the same time. Knowing their structure from the solid state, however, is not sufficient to rationalize their modus operandi in solution, because it is not guaranteed that their solid-state structure is retained. Our ECC Diffusion Ordered NMR SpecroscopY helps to reliably estimate their molecular weights, and hence facilitates the identification of all species present in solution. This opens the avenue to understand reaction pathways and provides ah andle for modifying reactivity. What was the biggest challenge? Hauser bases react with many other substrates because they are hot metal amides. In the established DOSY NMR spectroscopy an internal standard had to be added to provide ar eliable calibration curve. With Hauser bases this is most inconvenient, because it is difficultt of ind such suitable and inert molecules. So am ethod to establish an External Calibration Curve had to be developed first. Now this can be transferred to virtually any other system and will further provide rich insights to solution structures. What was the biggest surprise? The Hauser base structure we established in this paper is neither in tune with the solid-state structure nor with the well-founded predictions from colleagues. Although it persists in THF solution there is less solvent coordinated to the magnesium atom than in the solid-state structure. To our understanding it is that vacant coordination site that provides the reactivity to the substrate. Did you expect avery differentoutcome? If so, what was your initial guess? Yes, for sure!W et hought in THF solution there most likely is even more donor solvent coordinated to the metal cations and like other colleagues we would have predicted as olvent-separated ion pair. Invited for the cover of this issue are D. Stalkea nd R. Neufeld from the University of Gçttingen. The image symbolizes for the authors' navigation to the solution structure of the turbo-Hauser base, TMPMgCl·LiCl. Read the full text of the article at

Intermolecular Pummerer Coupling with Carbon Nucleophiles in Non‐Electrophilic Media

“…Without base, only as mall amount of the desired product 2a is formed (entry 1). Unlike the TMP-derived Hauser base 4a (entry 2), the presence of the DIPA-derivative 4b [15b] has ap ositive effect under these restrictive conditions,b ut cannot produce satisfactory yields of 2a.I nspired by the recent studies on Knochel-Hauser bases [17] (and in stark contrast to 4b), to our surprise we found that the rare DIPAMgCl·LiCl (4d) [18] promoted the formation of 2a in 91 %y ield (entry 5). [17b, 18] Thesynergy between an optimal Li/Mg ratio (entries 6and 7; see Tables S1 and S2 in the Supporting Information) and the specific diisopropylamide base (entries 4a nd 5) are both critical at enabling this reaction.…”

The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy

“…The other experimental methods suggested that a more complicated series of equilibria were actually occurring in solution [210]. Similar studies were conducted on other mixed metal complexes, such as the Hauser bases, iPr 2 NMgCl [211] and TMPMgCl [212] and their turbo-derivatives, revealing that the Schlenk equilibrium can be replaced by a more complicated series of equilibria between different aggregations states and identifying the effect of more hindered amides [213] on the solution phase structures. Other alkaline earth metal species characterised by diffusion NMR methods and external calibration calculations include s-block bimetallic catalysts containing two magnesium atoms, stabilised by differing amounts of Na(THF) 3 depending on the solvent used [214], and multinuclear complexes of calcium-and containing π ligands [215].…”

Suitability of Carbazolyl Hauser and Turbo‐Hauser Bases as Magnesium‐Based Electrolytes

“…1 H, 29 Si and 13 C{ 1 H} NMR spectra were recorded on Bruker Avance III 400 (BBO, BBFO probes), Avance III HD 500 (BBO Prodigy probe) or Avance III HD 600 (TCI cryo probe) spectrometers. Chemical shifts are reported in parts per million relatively to SiMe 4 ( 1 H, 13 C) as an external standard referenced to the solvents residual proton signal using xiref AU program for 7 Li-NMR spectra. DOSY-NMR spectra were measured using the ledbpgp2 s standard pulse sequence.…”

“…[6] Expectedly, equilibria between diverse species have been observed in solution by DOSY-NMR spectroscopy. [5,7] The preparation of these turbo-Hauser bases proceeds smoothly by deprotonation of secondary amines with Grignard reagents in the presence of lithium halide or with turbo-Grignard reagents such as iPrMgCl • LiCl. [8] Besides the widely used application of Hauser and turbo-Hauser bases as selective metalation reagents, we are interested in magnesium batteries.…”