Bildung siliciumorganischer Verbindungen. CVII. Bildung und Struktur des trans-trans-trans-Nonamethyl-hexasilaperhydrophenalens

Article abstract of DOI:10.1016/0022-328X(88)89067-3

trans-trans-trans-2,2,4,6,6,8,10,10,12-Nonamethyl-2,4,6,8,10,12-hexasilaperhydrophenalene 6 (m.p. 170 deg C) is formed from the substituted cyclic carbosilane 3 at 25 deg C (5 h) in the presence of AlBr3 by elimination of SiMe4.At 35 deg C (5 h) the formation of the all-cis-isomer 6a is observed in addition to 6.On the other hand the thermal transformation of 6 into 6a was not observed below 420 deg C.None of the other possible isomers were detected.Compound 6 reacts with MeLi to give 7 via lithiation of the central C atom.The hydrolysis of 7 leads to a mixture of 6 and 6a in a 2/1 ratio.Compound 6 crystallizes orthorhombically space group P2₁2₁2₁ (no.19); a = 2221.3, b = 1651.3, c = 667.3 pm; Z = 4; 2169 hkl; R = 0.053).Owing to the different size of the substituents on both sides of the polycyclic system the molecule is arched and the six-membered rings are flattened.The Si-C bond lengths decrease progressively from the central C atom to the periphery of the molecule(188.5 to 186.2 pm).It is shown that only the curvature of the polycyclic system causes a decrease in the endocyclic bond angles at the Si atoms (to 108.2 deg) and an increase in those at the C atoms (to 118.0 deg) as well as the flattening of the six-membered rings.