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