In Situ Grignard Metalation Method for the Synthesis of Hauser Bases

Abstract

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R 2 N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R 2 N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR 2 ) 2 and MgBr 2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state.

Alkaline‐earth metal dimesitylphosphinites and their ether adducts – A structural study in solution and in the crystalline state

“…Metalation of 1 with diethylmagnesium and ethylmagnesium bromide in ethereal solution yielded the corresponding colorless ether adducts [(L)MgR(μ‐OPMes 2 )] 2 (L/R=thf/Et ( 2‐Et ); Et 2 O/Br ( 2‐Br )) as depicted in Scheme 1. Compound 2‐Br was also accessible via the in situ Grignard Metalation Method ( i GMM), [17] i. e. the addition of bromoethane to a suspension of an equimolar amount of dimesitylphosphane oxide and magnesium turnings. The 1 H NMR spectra of single crystals of the phosphinite 2‐Et , dissolved in [D 8 ]THF, show also signals of homoleptic Mg(OPMes 2 ) 2 due to an operative Schlenk equilibrium in solution.…”

“…[16] Metalation of 1 with diethylmagnesium and ethylmagnesium bromide in ethereal solution yielded the corresponding colorless ether adducts [(L)MgR(μ-OPMes 2 )] 2 (L/R = thf/Et (2-Et); Et 2 O/Br (2-Br)) as depicted in Scheme 1. Compound 2-Br was also accessible via the in situ Grignard Metalation Method (iGMM), [17] i. e. the addition of bromoethane to a suspension of an equimolar amount of dimesitylphosphane oxide and magnesium turnings. The reaction of 1 with halide-free [(dx)MgEt 2 ], synthesized via the dioxane method, [18] with two equivalents of 1 in THF gave the tris(tetrahydrofuran) adduct of homoleptic magnesium bis(dimesitylphosphinite) [(thf) 3 Mg(OPMes 2 ) 2 ] (2-thf) according to Scheme 2.…”

In Situ Generation of Magnesium‐ and Calcium‐Based Grignard Reagents for Amide Synthesis

“…The Hauser bases can be divided structurally into two types (Scheme 3), monomeric (type I ) and dimeric, halide‐bridged compounds (type II ). Type I is preferred for bulky amides or amides with secondary interactions such as carbazolates, [3f] substituted carbazoles [tetra‐ tert ‐butylcarbazolate [25] or 2,9‐diaryl‐4,7‐di‐ tert ‐butylcarbazolate (aryl=Mes, [25] 9’‐Ph‐Anthr), Ph=phenyl], [26] and perfluorinated diphenylamides [27] …”

Synthesis of Sterically Encumbered Alkaline‐Earth Metal Amides Applying the In Situ Grignard Reagent Formation

“…Direct metalation of amines with magnesium and calcium is not viable due to the inertness of these metals even after activation (e. g. as powders or amalgams). To circumvent multiple‐step procedures (preparation of Grignard reagent solution, magnesiation of amine, addition of stoichiometric amounts of anhydrous MgX 2 and LiX) the in situ Grignard Metalation Method (iGMM, [6] Scheme 1) proves to be highly advantageous. Here, bromoethane is added to an ethereal suspension of Mg turnings and amine yielding Hauser bases.…”