MgMe 2 ( 1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe 2(thf)} 2(μ-dabco)] ( 2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt 3, and tmeda ( N, N, N′, N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme ( 5); NEt 3 ( 6); tmeda ( 7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] ( 8) were obtained. Reactions of MgMeBr with pmdta ( N, N, N′, N″, N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] ( 9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) · MgBr 2(pmdta) ( 10) and [{MgMe 2(pmdta)} 7{MgMeBr(pmdta)}] ( 11) in 24% and 2% yield, respectively, as well as [MgMe 2(pmdta)] ( 12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and 1H and 13C NMR spectroscopy. The coordination-induced shifts of the 1H and 13C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe 2(pmdta)] ( 12) and [MgBr 2(pmdta)] ( 13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent 1H NMR spectroscopic measurements (from 27 to −80 °C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf ( 4); diglyme ( 5); NEt 3 ( 6); tmeda ( 7)) in thf-d 8 solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at −80 °C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4– 6 whereas in the case of the tmeda complex 7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] ( 9) in thf-d 8 revealed no dismutation into [MgMe 2(pmdta)] ( 12) and [MgBr 2(pmdta)] ( 13) even up to −100 °C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] ( 9c), [MgMe 2(pmdta)] ( 12c), and [MgBr 2(pmdta)] ( 13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ⇌ 12c + 13c) was calculated to be K gas = 2.0 × 10 −3 (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be K thf = 1.2 × 10 −3 and K ether = 3.2 × 10 −3 (298 K), respectively.