Alkaline Earth Metal-Phosphorus Cages of the Type M_2nP_2m: Synthetic Approach and Topological Relations

Abstract

The metalation of triisopropylsilyl- and tri(tert-butyl)silylphosphane with alkaline earth metal bis[bis(trimethylsilyl)amides] yields the corresponding phosphanides. Depending on the stoichiometry, the dimeric and heteroleptic or homoleptic derivatives [(Me₃Si)₂N]_nM₂[μ-P(H)SiR₃]_4-n with n = 0, 1, and 2 are isolated and can be regarded as steps on the way to M_2nP_2m cage compounds in which the ratio n/m can vary between 1/2 [metal bis(phosphanides)] and 1/1 (metal phosphandiides). The metalation of triisopropylsilyl- and tri(tert-butyl)silyl-phosphane with dibutylmagnesium gives Mg_2nP_2m cages with n/m = 1/1, 2/3, and 4/5. The heavier alkaline earth metals form M_2nP_2m cages with n/m = 1/2 and 3/4 (M = Ca, Sr, Ba) in which the ratio n/m = 1/2 represents the homoleptic dimeric alkaline earth metal bis(phosphanide). All these cages can be derived from a M₂P₂ cycle which appears dimeric (M₄P₄ heterocubane) or trimeric (hexagonal M₆P₆ prism) in which two opposite planes can be capped by alkaline earth metal bis(phosphanide) molecules.

Keywords::

• Alkaline Earth Metals
• Cages
• Metalations
• Phosphandiides
• Phosphorus