Anionic phosphinomethanides as building blocks for heterocycles containing elements of group 2 and 12

Anionic phosphinomethanides are very soft donors to coordination centers. Though at least the light earth alkaline metals are extremely hard acceptors and therefore normally do not form stable complexes with e.g. phosphine ligands, various complexes of Be, Mg, Ca or Sr with one or more metal to phosphorus bonds can be obtained with this type of anionic ligands. The complexes obtained possess a spiroeyclic or tricyclic backbone, depending on the nature of the phosphinomethanide and the metal. Diphosphinomethanides even form complexes with Be and Mg, where no other metal to ligand contacts are observed than metal-phosphorus bonds. In addition, also the metals of the zinc triad are included in the investigation. Most noteworthy, beryllium and zinc complexes with a given phosphinomethanide ligand turn out to be essentially isostructural, despite their highly different radii, which is explained by the covalent contribution to the bonding in these complexes.