Highly Selective Synthesis of Hydrosiloxanes by Au-Catalyzed Dehydrogenative Cross-Coupling Reaction of Silanols with Hydrosilanes

We report a highly selective synthesis of siloxane building blocks containing <i>SiH</i>₂ <i>or SiH</i> functionalities. AuCl­(PPh₃)/PPh₃ or AuCl­(PPh₃)/P^<i>n</i>Bu₃ system catalyzed the reaction of trihydrosilanes with silanols giving <i>SiH</i>₂-containing siloxanes exclusively. On the other hand, a highly selective reaction of dihydrosilanes with silanols to afford <i>SiH</i>-containing siloxanes was achieved by simply changing the phosphine ligand to a bidentate one, xantphos. Usefulness of <i>SiH</i>₂-containing siloxanes was demonstrated by the synthesis of a trisiloxane, Et₃SiOSi­(Ph)­(H)­OSi^<i>t</i>BuMe₂, and a pentasiloxane, Ph₂Si­(OSiHPhOSiEt₃)₂, bearing <i>SiH</i> functionalities

Acid-Catalyzed Condensation Reaction of Phenylsilanetriol: Unexpected Formation of <i>cis,trans</i>-1,3,5-Trihydroxy-1,3,5-triphenylcyclotrisiloxane as the Main Product and Its Isolation

<i>cis,trans-</i>1,3,5-Trihydroxy-1,3,5-triphenylcyclotrisiloxane was successfully isolated and fully characterized by spectroscopic methods and single-crystal X-ray diffraction. This compound was believed to be highly unstable and only exist as a transient species in low concentration during the condensation reaction of phenylsilanetriol or its precursors. The isolated pure cyclotrisiloxane is, however, surprisingly stable even in acidic solution and partially isomerizes to the <i>cis,cis</i> isomer