Organogallium(ii) compounds bearing chelating ligands, bridging versus terminal co-ordination of gallium–gallium single bonds

Tetrakis[bis(trimethylsilyl)methyl]digallane(4) 1 containing gallium atoms in an oxidation state of +II and a Ga–Ga single bond is a versatile starting compound for the synthesis of a broad variety of derivatives. One of the most exciting reactions is the substitution of alkyl groups without cleavage of the Ga–Ga bond, which succeeds by the treatment of 1 with chelating protonic acids such as carboxylic acids and acetylacetone derivatives. In all cases, two chelating ligands were introduced, which depending on their structural parameters either occupy terminal positions with each one co-ordinated to only one gallium atom or bridge the Ga–Ga bond. The reason for the different co-ordination behavior is discussed here.