SYNTHESIS AND STRUCTURE OF A DIPHOSPHA-2,3,4,6,7,8-HEXASILABICYCLO[3.2.1]OCTANE WITH AN NEW CYCLOSILAPHOSPHANE SKELETON

The reaction of tert-butyl-tris(chlorodimethylsilyl)silane 1 with thre e mole-equiv. [LiPH2(dme)] in THF from -40 to 25 degrees C surprisingl y furnishes the novel bicyclic cyclosilaphosphane 3, which has been is olated in the form of colorless crystals in 29% yield. The practically unstrained Si6P2 skeleton in 3 is a constitutional isomer of the high er symmetric 1,4-Diphospha-2,3,5,6,7,8-hexasilabicyclo[2.2.2]- octane. Multinuclear-NMR spectroscopic investigations and a single-crystal st ructure analysis prove the constitution of 3. Whereas the SI-P distanc es are without peculiarity, the Si-Si distances in the Si-2 and Si-3 b ridges are significantly different. This can be explained by different magnitudes of through bond interactions between the n-orbitals at pho sphorus and the sigma acceptor orbitals of the Si-Si bonds which depe nd on the bridge lengths and are in analogy to the electronic features observed in iphospha-2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane.