Closo solubility

Precise placement of metal complexing sites within the infrastructure of a cascade molecule is of importance from a variety of perspectives. In the construction of the above noted Micellane family (cf. Sect. 3.1), we reported the construction of dendrimers with four alkyne moieties at sites equidistant from each other in the interior (17, Fig. 8) [60]. These were treated with decaborane (B10H14) to afford 1,2-dicarba-closo-dodecaboranes (o-carboranes) [71]. Rendering boron clusters soluble in water is of interest because of their use in cancer treatment by Boron Neutron Cancer Therapy. First and second generation water-soluble dendrimers containing four and twelve precisely located boron cluster sites, respectively, were synthesized (e.g., 18). These water soluble dendrimers and their precursors were characterized by 13C-, and nB-NMR spectroscopy (Fig. 8). 

Therefore, the simplest strategy to increase the water solubility of C2B10-containing compounds is degradation of the closo-cage to the nido-anion, and this has been applied to C2Bio-containing amino acids and porphyrins (see Scheme 2.2-13). 

The early stages of the hydrolysis-condensation of [M(OR)n]m can be characterized by x-ray diffraction for oxophilic metals (Table 4). These include centrosymmetric polynuclear oxoalkoxides of titanium, zirconium, and niobium. Their stmcture is often related to that of polyoxoanions TiyOalOEOao is isostructural with Mo7024, and Nb80io(OEt)20 has a cagelike structure that compares well with that of the paratungstate H2Wi2042 b-. These oxoalkoxides are soluble as a result of their closo structure, and NMR has been developed as a technique to follow the hydrolysis of titanium(IV) alkoxides with... 

The synthesis and the basic physical-chemical properties of BNCT agents such as neutral octa-closo-carboranyl-alkylthio-porphyrazines and their water-soluble counterparts obtained by mild deboronation of the closo-polyedra were described by Pietrangeli and Ricciardi (2009). These compounds show negligible cell toxicity and good cellular uptake. 

These are shown in Figure 14.22. The B12H.12 anion, known officially as the dodecahydrododecaborate anion, is a perfect icosahedron and is one of the most stable molecular ions known. It is also highly water-soluble and incredibly heat-resistant. Table 14.6 shows the relationship between the closo, nido, and arachno structural classes starting with four of the closo dianions, (n = 6, 7,... 

However, the chemistry of c/oi o-decaborate is much less studied than the c/oio-dodecaborate chemistry. The carba-c/oio-dodecaborate anion [CB,H,2] combines advantages of both its iso-structural and isoelectronic analogs, [C2B10H12] and [B,2H,2] the good solubility in water as the sodium salt and the presence of carbon atom available for functionalization using standard methods of organic chemistry [20], It should be noted that the practical importance of the cwha-closo-dodecaborate anion was very limited up to recently when convenient methods for the synthesis of the parent cluster and its C-phenyl derivatives were developed [21], A few examples of incorporation of [CBiiHi2] into various porphyrins have been reported quite recently [22],... 

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