Zur Synthese der Heptaphospha-nortricyclane R3P7R = Et,i-Pr,n-Bu,i-Bu,SiH2Me,SiH3, Et2P–SiMe2

Concerning the Synthesis of the Heptaphospha-nortricyclanes R₃P₇ R = Et, i-Pr, n-Bu, i-Bu, SiH₂Me, SiH₃, Et₂P—SiMe₂ The preparative access to the compounds Et₃P₇ 1 ,i-Pr₃P₇ 2 ,n-Bu₃P₇ 3 ,i-Bu₃P₇ 4 , (H₃Si)₃P₇ 5 , (MeH₂Si)₃P₇ 6 , and (Et₂P—SiMe₂)₃P₆ 7 through the reaction of Li₃P₇ · 3 DME with either EtBr, i-PrBr, n-BuBr, H₃SiI, MeSiH₂Br or Et₂P—Sime₂Cl, respectively, is described. At 20°C the compounds 1 to 4 are yellow-greenish, viscid liquids (viscosity increases with the size of R), which are well soluble in ethers and non-polar solvents. 5 forms colorless crystals, which (similar to those of 6 ) decompose, when exposed to sunlight. 6 and 7 are generated quantitatively, these compounds, however, cannot be isolated undecomposed. While the formation of 1 occurs quantitatively via the red intermediate Li₂EtP₇, it is possible to isolate Li(i-Pr)₂P₇ from the residue of the reaction leading to i-Pr₃P₇. This Li-phosphide is said to cause the formation of higher, P-rich phosphanes like i-Pr₃P₉. Treatment of Li₃P₇ with (Me₃C)₃SiBr does not yield (Me₃C)₃Si]₃P₇. The ratio R₃P₇(sym.): R₃P₇(asym.) — being 1:3 in Et₃P₇ or Me₃P₇-shifts with increasing size of R, favouring the symmetrical isomer. There are no hints for the formation of an asymmetrical isomer in (H₃Si)₃P₇ — as already known from (Me₃Si)₃P₇, where an asymmetric isomer does not exist either.