Magnesiation of triisopropylsilylphosphane: Synthesis and structures of new Mg2nP2m polyhedra

The magnesiation of triisopropylsilylphosphane with dibutylmagnesium in tol uene yields the octanuclear complex [Mg-8((PSiPr3)-Pr-i)(6){P(H)(SiPr3)-Pr- i}(4)] (1) which consists of (MgPSiPr3)-Pr-i units forming a hexagonal Mg6P 6 prism, with two opposite Mg2P2 moieties capped by additional Mg[P(H)(SiPr 3)-Pr-i](2) groups. If a small amount of THF is present during the metalati on reaction [(THF)(4)Mg-6((PSiPr3)-Pr-i)(6)] (2) also containing a hexagona l Mg6P6 prism can be isolated. The magnesiation of H2P-(SiPr3)-Pr-i in tetr ahydrofuran leads to the formation of the tetrameric complex [(THF)(MgPSiPr 3)-Pr-i](4), (3) with a slightly distorted Mg4P4 cubane-like structure. The structures depend strongly on the steric strain caused by the trialkylsily l substituents and the neutral coligands at the magnesium center. The highe st steric strain, which is induced by coordination to every magnesium atom, leads to the smallest MgnPn polyhedron - the central Mg4P4 heterocubane mo iety. In compounds 1 and 2 the hexagonal Mg6P6 prism is formed, however, wi th reduced steric strain as observed for 2 where the Mg-P bond lengths beco me more similar.