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.