Synthesis and reactivity towards DIBAL-H of Cyclo-Siloxanes cyclo-[R2SiOSi(Ot-Bu)2O]2, cyclo-(t-BuO)2Si(OSiR2)2O, and cyclo-R2Si[Osi(Ot-Bu)2]2O (R=Me, Ph)

The six-, eight- and twelve-membered cyclo-siloxanes, cyclo-[R₂SiOSi(Ot-Bu)₂O]₂ (R = Me (1), Ph (2)), cyclo-(t-BuO)₂Si(OSiR₂)₂O (R = Me (3), Ph (4)), cyclo-R₂Si[OSi(Ot-Bu)₂]₂O (R = Me (5), Ph (6)) and cyclo-[(t-BuO)₂Si(OSiMe₂)₂O]₂ (3a) were synthesized in high yields by the reaction of (t-BuO)₂Si(OH)₂ and [(t-BuO)₂SiOH]₂O with R₂SiCl₂ and (R₂SiCl)₂O (R = Me, Ph). Compounds 1 - 6 were characterized by solution and solid-state ²⁹Si NMR spectroscopy, electrospray mass spectrometry and osmometric molecular weight determination. The molecular structure of 4 has been determined by single crystal X-ray diffraction and features a six-membered cyclo-siloxane ring that is essentially planar. The reduction of 1 - 6 with i-Bu₂AlH (DIBAL-H) led to the formation of the metastable aluminosiloxane (t-BuO)₂Si(OAli-Bu₂)₂ (7) along with Me₂SiH₂ and Ph₂SiH₂.