Complexes of the B7C2H92- Ligand

The cesium salt of (B7C2H9)2Co (I) can be rearranged at 315°C in 24 hours to an isomeric product (III) in almost quantitative yield (6). The cyclopentadienyl derivative (A) can also be rearranged under the same conditions to a new isomer (B). The low-field doublet present in the nB NMR spectra of (I) and A is not seen in the spectra of the products. The 

A third isomeric species (II) has been isolated when B7C2H,, 2 is reacted with cobalt(ll) chloride at 70° C. This compound has only one carborane (CH) resonance in the proton NMR, suggesting that the two carbon atoms occupy equivalent positions in the cage. The favored structure of the three possible choices is illustrated in Fig. 10 (II). This choice is based on the 

Two electrophilic substitution reactions of neutral complex A have been reported. These are Friedel-Crafts acetylation and bromination. The proposed positions of substitution are indicated in Fig. 11 (20). 

When B7C2Hn2- was treated with BrMn(CO)5 at reflux in tetrahydro-furan, the expected B7C2H9 complex was not isolated. Instead a 48% yield of a new type of complex, (B6C2H8)Mn(CO)3, was obtained (15). The 11B NMR spectrum contained a 1 2 2 1 pattern of doublets. The proton NMR spectrum suggested that the two carborane CF1 units are equivalent. 

Based on these data, the structure shown in Fig. 12 was proposed. This is a symmetrically tricapped trigonal prism in which the manganese atom occupies a vertex of the trigonal prism. 

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