Cage fusion

B3.5 Cluster-forming and cage fusion in metallacarborane chemistry... 

In the area of synthesis, the structural and theoretical framework contributed by Lipscomb provided a foundation for the monumental synthetic work of M. F. Hawthorne and his students, who transformed boron cluster chemistry first by their synthesis of the polyhedral borane anions BioHio and Bi2Hi2 (30) and later by the synthesis of metallacarboranes (31). In our own laboratory, considerations of charge distribution in borane anions (14) prompted us to explore reactions of transition metal ions with small borane and carborane anions (32). This, in turn, led to a number of advances including the first closed polyhedral metallaboranes (33), the discovery of metal-induced oxidative cage fusion (34), and the synthesis of B12H16, the only neutral Bi2 hydride, via metal-promoted fusion of BeHQ (35)... 

Reduction of the pentaalkyl-1,5-dicarba-closo-pentaboranes(5) 44 with elemental K opens the cluster and subsequent reaction with I2 enforces oxidative fusion of two C2B3 units to give a C4B6 cage (Scheme 3.2-36). The peralkylated hexaboraadamantane derivatives 70 (R = Me, Et X-ray structure analysis for R = Me [89]) rearrange irreversibly into the carboranes 71 with a wido-C4B6 framework [89] (X-ray structural analysis for R = Et [90]). The structure of the nido-C Bf, cluster is fluxional in solution [91]. 

All fullerenes (C ) are composed of sp2 hybridized carbon atoms forming a 3-D network of fused (n - 20)/2 six-membered and 12 five-mem-bered rings. As enshrined in the Isolated Pentagon Rule (IPR), so far, none of the structures isolated have two pentagons fused together. The curvature of the cage results in some strain, and the three angles around a carbon atom sum to 348° instead of the ideal value of 360° for . The [6,6] fusions have most double-bond character and are invariably where complexation occurs. For there are 30 such equiva-... 

X-ray diffraction and NMR studies have shown that metal fragments add exclusively across the [6,6] fusions to give rj2-type adducts. In contrast, organic derivatives add either to the [6,6] to form a closed adduct, or to the [6,5] fusions to form either an open or closed adduct (66). The ease with which some metal fragments dissociate off and on to the cage, in contrast to the organic derivatives, may explain the exclusive formation of the thermodynamically most stable [6,61-adducts. 

The basic structural unit of Agi2(C2)2(CF3CO2)8(2-pyzCONH2)3C0mprises the fusion of a distorted triangulated dodecahedral Ags cage containing an embedded C f dianion and an open fish-like Ag6(//6-C2) motif... 

Grimes153 have prepared 11-13 atom nido-cages by the insertion of transition metal atom moieties into carboranes. Recently, 13 and 15-vertex m rfo-carboranes have been prepared by Hosmane and Grimes1S4) by the oxidative fusion of carboranes and borane anions. 

The Incorporation of [a,c]-Fusion into the Molecular LEGO Set — The Synthesis of Angular Belts and Cages... 

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