Verbrückende Koordination von Gallium–Gallium‐Bindungen durch Chelatliganden – Grenzen der Beständigkeit von Digallium‐Verbindungen

Bridging Coordination of Gallium–Gallium Bonds by Chelating Ligands – Limitations of the Stability of Digallium Derivatives The reactions of bis[bis(trimethylsilyl)methyl]‐di(μ‐acetato)digallium(Ga–Ga) ( 2 ) with lithium‐2‐amido‐1‐methylbenzimidazole in the molar ratios of 1 to 1 or 1 to 2 yielded by the precipitation of lithium aceatate new digallium compounds, in which the intact Ga–Ga bonds were bridged by two chelating ligands. The replacement of only one acetato group gave compound 5 , that possesses two different bridging ligands with the benzimidazole group coordinated by its terminal amido function and that nitrogen atom of the heterocycle which is not attached to a methyl group. If both acetato groups were replaced by imdazole ligands, two products were obtained, in which the chelates are transferred in each other either by a mirror plane parallel to the Ga–Ga bond (cis, 6 ) or by a twofold rotational axis perpendicular to the element–element bond (trans, 7 ). 7 is thermodynamically favored and was irreversibly formed by heating of the mixture. 5 and 7 were characterized by crystal structure determinations and have Ga atoms in a chiral environment. Weaker donor ligands such as diphenyl(lithiomethyl)(piperidinomethyl)silane, which in principal is able to coordinate via its carbanionic carbon atom and more weakly via its sterically shielded piperidino nitrogen atom, led to the cleavage of the Ga–Ga bond. The mononuclear compound 8 was isolated, in which the Ga atom is attached to one bis(trimethylsilyl)methyl group and two (piperidinomethyl)silyl substituents. Furthermore, the synthesis of a dialkyl‐bis(1,3‐dionato)digallium derivative ( 9 ) is reported, in which the chelating 1,3‐dionato groups are terminally coordinated to the Ga atoms of the unsupported Ga–Ga bond.