Functionalized borazines as precursors for new silica gels

Abstract

Trialkynylborazines have been prepared in excellent yields by reacting alkynyl-bis(diisopropylamino)borane with powdered ammonium chloride in toluene. These were subsequently used in hydrosilylations with trichlorosilane and trialkoxysilanes using platinum on charcoal as heterogeneous catalyst. This reaction is stereoselective and gives the β-isomers as major product. The tris(β-tricholorsilylvinyl)-substituted derivative (Cl₃SiCHCH)₃B₃N₃H₃ was isolated in pure form and transformed into a highly functionalized silica gel by a sol–gel process. This gel has a specific surface of about 315 m² g⁻¹ and is the first containing intact borazine rings. The structures of (iPr₂N)₂B–CCH, B,B′,B″-(HCCH)₃B₃N₃H_3,B,B′,B″-(Me₃SiCCH)₃B₃N₃H₃ and B,B′,B″-(Cl₃Si–CHCH)₃B₃N₃H₃ were determined by X-ray structure analyses and are reported.