Selective synthesis of eight-membered siloxane rings with different substituents on the silicon atoms

Abstract The selective synthesis of eight-membered silicon-oxygen rings of the general formula (R 2 Si) 2 (R′ 2 Si) 2 O 4 can be achieved using the auxiliary reagent hexabutyldistannoxane. In a first step, the cycles [CH 2 –N(R)] 2 SiCl 2 [R = t Bu ( 1 ), Ph ( 2 )] are reacted with the double molar amount of hexabutyldistannoxane to form [CH 2 –N(R)] 2 Si(OSnBu 3 ) 2 3 (R = t Bu) and 4 (R = Ph). The syntheses are carried out without any solvent. The distannoxosilanes 3 and 4 are transformed to the eight-membered siloxane rings (R 2 Si) 2 (R′ 2 Si) 2 O 4 {R 2 = [CH 2 –N( t Bu)] 2 , R′ = Cl ( 5a ), R 2 = [CH 2 –N( t Bu)] 2 , R′ = Br ( 5b ), R 2 = [CH 2 –N(Ph)] 2 , R′ = Me ( 6 )} using either SiCl 4 , SiBr 4 or Cl 2 SiMe 2 as reactants at ambient temperature. The selective cleavage of the silicon–nitrogen bonds in 6 by addition of a solution of HCl in tetrahydrofuran leads to the chloro- and methyl-substituted cyclotetrasiloxane (Me 2 Si) 2 (Cl 2 Si) 2 O 4 ( 7 ). The new cyclotetrasiloxanes 5 – 7 have been characterised by spectroscopic methods as well as by single crystal X-ray analyses, revealing Si 4 O 4 eight-membered cycles with different substituents on the silicon atoms. Depending on the substitution pattern at silicon atoms, varying Si–O bonds and angle are found. To cite this article: M. Veith et al., C. R. Chimie 6 (2003) 000–000 .