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

Lithium-ion batteries pose certain drawbacks and alternatives are highly demanded. Requirements such as low corrosiveness, electrochemical stability and suitable electrolytes can be met by magnesium-ion batteries. Metalation of carbazole with Mg in THF in the presence of ethyl bromide yields the sparingly soluble Hauser base [(thf)$_{3}$Mg(Carb)Br] (1) which shows a Schlenk-type equilibrium with formation of [(thf)$_{3}$Mg(Carb)$_{2}$] and [(thf)4MgBr2]. A THF solution of 1 shows a low over-potential and a good cyclability of electrodeposition/-stripping of Mg on a Cu current collector. An improved performance is achieved with the turbo-Hauser bases [(thf)(Carb)Mg(μ-Br/X)$_{2}$Li(thf)$_{2}$] (X=Br (2) and Cl (3)) which show a significantly higher solubility in ethereal solvents. The THF solvation energies increase from (thf)$_{x}$MgBr$_{2}$ over (thf)$_{x}$Mg(Carb)Br to (thf)$_{x}$Mg(Carb)$_{2}$ for an equal number x of ligated THF molecules.