The [2,5,12-C3B8H15]− anion, the first representative of the eleven-vertex hypho family of tricarbaboranes

Abstract

In one synthetic step from the readily available 9-Me₂SCH₂-nido-7,8-C₂B₉H₁₁ (compound 1), the first representative of the eleven-vertex hypho family of tricarbaboranes, [2,5,12-C₃B₈H₁₅][X] (X[NMe₄]⁺ or [PPh₄]⁺) (compound 2), has been isolated in 32% yield and structurally characterised by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy, mass spectrometry, and computational methods. Both [NMe₄]⁺ or [PPh₄]⁺ salts of anion 2 were found to undergo degradative conversion to the [hypho-6,7-C₂B₆H₁₃]⁻ anion (anion 3) in alkaline medium. The [PPh₄]⁺ salt of anion 2 converted quantitatively to the [6-CH₃-arachno-5,10-C₂B₈H₁₂]⁻ anion (anion 4) if passed through a silica column or to the neutral 5-CH₃-arachno-6,9-C₂B₈H₁₃ (compound 5) on treatment of its [NMe₄]⁺ salt with dilute HCl. Moreover, the reaction of compound 2 with [RhCl₂(C₅Me₅)]₂ afforded the eleven-vertex ruthenadicarbaborane [1-C₅Me₅-4-CH₃-closo-1,2,3-RhC₂B₈H₉] (compound 8). All these reactions resulted in an extrusion of one of the cluster carbon atoms into an exoskeletal position.