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