S. P. Knyazev

The structure of a new isomer of dicarba-nido-undecaborane(13)

Abstract The intramolecular rearrangement involved in the electrophilic methylation of 7,8-B9C2H112− leads after protonation to the methyl derivative of a new isomer of dicarba-nido-undecaborane(13). By an X-ray structure analysis the latter compound is shown to be 11-methyl-2,7-dicarba-nido-undecaborane(12). It has the structure of an icosahedron with one missing vertex, with the carbon atoms adjacent, one in the open face of the polyhedron and the other in its closed part. The methyl group is attached to the boron atom of the open face bonded to both carbon atoms. The open face has two BHB-bridges which are symmetric relative to its carbon atom. The main interatomic distances are: av. BB 1.794(8), av. BC 1.685(7), CC 1.606(6), BMe 1.551(8), av. BH (terminal) 1.08(3), av. BH (bridging) 1.26(4), av. CH 0.92(4) A.

Two isostructural carboranes: 3-phenyl-1,2-dicarba-closo-dodecaborane(12) and 1-phenyl-1,7-dicarba-closo-dodecaborane(12)

Two phenyl-substituted carboranes, 3-phenyl-1,2-dicarba-closo-dodecaborane(12), C8H16B10, (I), and 1-phenyl-1,7-dicarba-closo-dodecaborane(12), C8H16B10, (II), were found to be isostructural. Comparison of the bond angles at the ipso-C atoms of the phenyl substituent for (I) and (II) [117.71 (3) and 118.45 (10) degrees, respectively] indicates that electron donation of the carborane cage for B- and C-substituted carboranes is different.

2‐Methyl‐1‐propenyl‐1,2‐dicarba‐closo‐dodecaborane(12)

The title compound, C6H18B10, is the first X-ray investigated carborane with a propenyl substituent. The C—C bond length in the carborane cage is 1.688 (2) A.

Synthesis and the structure of tribromo(7-bromobicyclo[4.1.0]hept-7-yl)germane

A general procedure was developed for the synthesis of halocyclopropylgermanes. This procedure was used for the preparation of tribromo(7-bromobicyclo[4.1.0]hept-7-yl)germane. The molecular structure was established by GLC-mass spectrometry, 1H NMR spectroscopy, and X-ray diffraction analysis.

The crystal and molecular structure of cesium 9,10,11-trimethyl-7,8-dicarba-nido-undecaborate(1-) Cs[9,10,11-Me3-7,8-C2B9H9]

ConclusionsBy a complete x-ray diffraction study of cesium 9,10,11-trimethyl-7,8-dicarba-nido-undecaborate(1-) we proved the axial orientation of the Me group attached to the B10 atom of the open face of the nido-carborane polyhedron. This serves as an additional proof of the stereospecificity of the alkylation reaction of the dicarbollide ions and the necessity for a migration stage of the boron atom with the substituent to the site of the deficient apex of the icosahedron to form a derivative with an equatorial disposition of the alkyl group.