Alkaline earth metal-phosphorus cages of the type M2nP2m: Synthetic approach and topological relations

The metalation of triisopropylsilyl- and tri(tert-butyl)silylphosphane with alkaline earth metal bis[bis(trimethylsilyl)amides] yields the correspondi ng phosphanides. Depending on the stoichiometry, the dimeric and heterolept ic or homoleptic derivatives [(Me3Si)(2)N](n)M-2[mu -P(H)SiR3](4-n) with n = 0, 1, and 2 are isolated and can be regarded as steps on the way to M2nP2 m cage compounds in which the ratio n/m can vary between 1/2 [metal bis(pho sphanides)] and 1/1 (metal phosphandiides). The metalation of triisopropyls ilyl- and tri(tert-butyl)silyl-phosphane with dibutylmagnesium gives Mg2nP2 m cages with n/m = 1/1, 2/3, and 4/5. The heavier alkaline earth metals for m M2nP2m 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(phospha nide). All these cages can be derived from a M2P2 cycle which appears dimer ic (M4P4 heterocubane) or trimeric (hexagonal M6P6 prism) in which two oppo site planes can be capped by alkaline earth metal bis(phosphanide) molecule s.