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-Me(2)SCH(2)-nido-7,8-C(2)B(9)H(11) (compound 1), the first representative of the eleven-vertex hypho family of tricarbaboranes, 2,5,12-C(3)B(8)H(15)]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-C(2)B(6)H(13)]- anion (anion 3) in alkaline medium. The PPh4]+ salt of anion 2 converted quantitatively to the 6-CH3-arachno-5,10-C(2)B(8)H(12)]- anion (anion 4) if passed through a silica column or to the neutral 5-CH3-arachno-6,9-C(2)B(8)H(13) (compound 5) on treatment of its NMe4]+ salt with dilute HCl. Moreover, the reaction of compound 2 with RhCl2(C(5)Me(5))]2 afforded the eleven-vertex ruthenadicarbaborane 1-C(5)Me(5)-4-CH(3)-closo-1,2,3-RhC(2)B(8)H(9)] (compound 8). All these reactions resulted in an extrusion of one of the cluster carbon atoms into an exoskeletal position.