N,N-dimethylcarbamato derivatives of magnesium starting from the metal oxide

Magnesium oxide reacts with dimethylammonium dimethylcarbamate, [Me2NH2][O2CNMe2], in toluene yielding the carbonato-carbamato complex [Me2NH2](3)[Mg-8(CO3)(2)(O2CNMe2)(15)] 1, which gradually loses [Me2NH2][O2CNMe2] upon mild heating or by lowering the carbon dioxide pressure to give products of intermediate composition (Me2NH2](n)[Mg-8(CO3)(2)(O2CNMe2)(12+n)] with n ranging from 3 to 0, the neutral complex [Mg-8(CO3)(2)(O2CNMe2)(12)], 2, being obtained upon exhaustive treatment in vacuo. The equilibria may be shifted back from 2 to I by using an excess of [Me2NH2][O2CNMe2]. The same products were obtained in low yields by reacting magnesium with [Me2NH2][O2CNMe2]: in this case the reaction proceeds slowly, being presumably promoted by the presence of some MgO and/or H2O. The crystal and molecular structure of I has been studied by single-crystal X-ray diffraction methods, the anion containing a ring of eight edge-or apex-sharing {MgO6} distorted octahedra, with Mg-O distances in the range from 1.921 to 2.313 Angstrom. The framework is kept together by two p.-carbonato ligands and by the fifteen carbamato ligands. The ionic aggregates [NH2Me2](3)[Mg-8(CO3)(2)(OCONMe2)(15)] are alternated in the crystal with heptane molecules and only weak van der Waals interactions are present between adjacent octanuclear aggregates, in agreement with the solubility of the substance in toluene. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.