PROPOSED STRUCTURE OF THE 1ST HYPHO CARBABORANE, C3B4H12

The reaction between arachno-B4H10 and propyne under hot/cold conditio ns affords in low yield the first unsubstituted neutral hypho carbabor ane, C3B4H12, a colourless volatile liquid. The new tricarbaborane has been characterized by high-resolution mass spectrometry and H-1, H-1{ B-11}, H-1{B-11 selective}, 2D H-1 - H-1{B-11} COSY, H-1{B-11} n.O.e., B-11, B-11{H-1}, 2D B-11 - B-11{H-1} COSY and C-13 NMR spectroscopy. The data imply a mirror-plane symmetry and are consistent with an unpr ecedented open seven-vertex carbaborane framework.