SYNTHESIS, STRUCTURE, AND REACTIVITY OF THE PERMETHYLATED DECASILANE (ME(3)SI)(3)SI-SIME(2)-SIME(2)-SI(SIME(3))(3)

The reaction between ClMe(2)SiSiMe(2)Cl and two equivalents of (Me(3)Si)(3)SiLi . 3THF resulted in a 40% yield of (Me(3)Si)(3)Si-SiMe(2)-SiMe(2)-Si(SiMe(3))(3), I. I crystallized in space group P (1) over bar, a = 9.229(2) Angstrom, b = 9.312(2) Angstrom, c = 13.709(3) Angstrom, alpha = 104.15(2)degrees, beta = 91.35(2)degrees, gamma = 114.64(2)degrees. The internal Si-Si bond lengths ((Me(3)Si)(3)Si-SiMe(2)) (B) and (Me(2)Si-SiMe(2)) (C) are equivalent at 237.5(1) pm and 237.4(2) pm, respectively, and marginally longer than the terminal Me(3)Si-Si bonds A which are in the range 234.5(1)-236.1(2) pm. The Me(3)Si-Si-SiMe(2) angle of 115.3(1)degrees and Me(3)SiSi-SiMe(2)-SiMe(2) angle of 117.1(1)degrees are the major structural deformations that reflect the steric complexity of the molecule. Photochemical irradiation of I in CCl4 leads to predominant cleavage of the central Si-Si bond C with minor cleavage of bond B; photochemistry in hexane is more indiscriminate, both B and C were homolytically cleaved but silylene eliminations and secondary reactions also occurred. Treatment with Li or MeLi led to cleavage of Si-Si bonds B and C. In the case of Li, predominant cleavage of B was observed (> 90%), whereas with MeLi cleavage took place at bond C (> 90%).