Ten-Vertex Metallocarboranes

The original preparation of ten-vertex metallocarboranes involved the deprotonation of the nido-carboranc 6,8-C2B7H13, followed by reaction with a transition metal halide. Additional hydrogen gas was liberated during the complexation, and cZoso-metallocarborane compounds were formed (38)  

Mixed-sandwich complexes could be synthesized by adding cyclopentadie-nide ion to the reaction mixture (38, 48). 

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

Another route to ten-vertex monometallocarboranes is through polyhedral expansion of 4,5-C2B7H9. A new isomer of C5H5C0C2B7H9 with carbon atoms in positions 3 and 10 is produced in this reaction. Side products included the nine-vertex species C5H5C0C2B6H8 (Section VIII) and the eleven-vertex C5H5C0C2B8H10 (24). 

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. 

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Ten-vertex metallocarboranes containing both cobalt and nickel in the same polyhedron have been synthesized from the nine-vertex anionic species C5H5C0CB7HS- (Section VIII) by polyhedral expansion (87). The resulting neutral complexes, of formula (C5Hs)2CoNiCB7H8 and con-... 

The chemical reactions of monometallic ten-vertex metallocarboranes have been examined (40). Fricdel-Crafts acylation of C5H6Co(l, 6-C2B7H9) produced a monosubstitution product. Attack occurred on the boron atom farthest removed from the polyhedral carbon vertices. No substitution on the cyclopentadienyl ring was observed. 

Reactions of monometallic eleven-vertex metallocarboranes have been discussed in previous sections and may be summarized briefly as (a) polyhedral expansion to bimetallic twelve-vertex complexes and (6) thermal metal transfer to bimetallic twelve-vertex compounds. Polyhedral contraction to ten-vertex monometallocarboranes is discussed in Section VII. 

The first metallocarborane of this geometry to be synthesized was an unexpected product. In an attempt to prepare a ten-vertex manganese carbonyl complex, the C2B7Hii2 ion, discussed in Section VII, was reacted with BrMn(CO)5. Surprisingly, the only metal-containing compound isolated from the reaction mixture had just 6 boron atoms (36, 50). The course of the reaction may be outlined as follows ... 

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