Vertex rearrangement

There is a special and very important feature of the anticipated open nido twelve-vertex structures in Fig. 12 repetition of single Lipscomb dsd rearrangements (denoted by the two-headed arrows) monotonically allows the six skeletal atoms about the open face to rotate about the second tier of five skeletal atoms (two-tier dsd rotation). Each dsd rearrangement [85, 163) (valence bond tautomerism) recreates the same configuration and involves only the motion of two skeletal atoms (in the ball-and-stick representation) and would allow carbons, if located in different tiers, to migrate apart. Such wholesale valence bond tautomerism is known to accompany the presence of seven-coordinate BH groups, e.g., and CBjoHu 142,155). 

XII- N12). Actually, carbon would prefer to be about the open face, which suggests that the ideal carbon positions upon the twelve-vertex nido skeleton would be those displayed in XIII-N12 and, given the fluxional characteristics that accompany seven-coordinate BH groups, intermediate XII-N12 should be able to rearrange into the more stable... 

On the other hand, there is no automorphism of the Mobius ladder of Figure 38 which could rearrange the vertices as illustrated in Figure 40. This is because the Mobius ladder of Figure 38 has vertex number 3 adjacent to vertex number 7, but the Mobius ladder of Figure 40 does not have these two vertices adjacent. 

These ten-vertex monometallic complexes exhibit thermal polyhedral rearrangements similar to those mentioned previously. In fact, they were... 

A novel ten-vertex bimetallocarborane, (CsHo C C BeHs, is produced upon the polyhedral expansion of 1,7-C2B6H8 (16). The expected monometallic nine-vertex species, C5H5CoC2B6H8, is also produced in this reaction (see Fig. 4). An X-ray crystal structure of the bimetallic product (61) showed the 2 cobalt atoms to occupy adjacent positions on the two equatorial belts of the bicapped square antiprism. The carbon atoms occupy the low-coordinate caps. Thermal rearrangement (30) produced an isomeric complex in which the metals are separated from each other, but the carbon atoms remain in the low-coordinate sites. 

The deltahedron for n = 10, a bicapped square antiprism, exhibits two four-connect and eight five-connect vertices. Hence, for one heteroatom in a ten vertex c/oso-cluster we have 1 - and 2-isomers and two heteroatoms in 1,10-, 1,6-1,2-, 2,3-, 2,4-, 2,6- 2,8-isomers. Different placements generate different cluster stabilities. A rule of thumb is that the more electronegative element prefers the lower-connectivity vertex. Multiple heteroatoms more electronegative than B prefer non-adjacent positions as far apart as possible. Rearrangement to the most stable isomeric form need not be fast. In the case of icosahedral clusters, for example, the barrier to rearrangement is large and isomers can be isolated. 

Compound 10 was found to undergo boron elimination upon treatment with ethanol to give the previously reported6 11-vertex complex 8, while thermal rearrangement of 10 at 350 °C leads to quantitative formation of the isomer 6. 

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