CZoso-Carboranes

Bigger cages, up to but not including seven-coordinate vertices (i.e., less steric strain), tend to accompany increased stability thus l,6-C2B4Ha (IV-C2) and 2,4-C2B5H7 (V-C2) are progressively more stable. Compound C2BgHg (VI-C2) is apparently even more stable and, incidentally, is the only parent cZoso-carborane that is comprised of a dl-pair (172). 

A third group of unstable or unknown cZoso-carboranes is displayed in Fig. 4. 

Spencer, Green, and Stone (88) have recently described a new synthetic approach to metallocarboranes in which an organomctallic transition metal complex is thermally reacted with a neutral cZoso-carborane, resulting in the incorporation of the metal into the polyhedron ... 

The following reaction sequence leading to these complexes is believed to be similar to the stepwise reactions in which metallocarborane complexes are formed from neutral cZoso-carboranes ... 

Schirrmacher, E. Schirrmacher R. Beck, C. Mier, W. Trautman, N. Rosh, R Synthesis of a Tyr(3)-octreotate conjugated cZoso-carborane [HC2B10H10] a potential compound for boron neutron capture therapy. Tetrahedron Lett. 2003, 44, 9143-9145. 

FIGURE 22.15 Bis(phosphonito)-cZoso-carboranes investigated in hydroformylation. 

Even though the cZoso-carborane clusters are structures showing high stability with respect to strong acids, they react with Lewis bases yielding more opened structures, known as nido, by a partial deboronation process that implies the loss of a cluster s vertex. Several nucleophiles such as... 

FIGURE 10. (a) (He I) PE spectrum of l,2-dimethyl-l,2-disila-cZoso-dodecaborane(12) ((H3CSi)2 BioHio) with Koopmans assignment by MNDO eigenvalues as well as cluster orbital diagrams for the three radical cation states of lowest energy (b) comparison of MNDO charge distributions for both 1,2-carborane as well as 1,2-bis(silamethyl)-c/oso-dodecaborane(l 2)... 

Two methods have been reported for the preparation of closo-1,2-dicarbadodecaborane(12) (or(/io-carborane). The first procedure involves the direct reaction of acetylene with a (Lewis base)2BioHi2 compound. The second procedure involves the oxidative degradation of l,2-bis(hydroxymethyl)-cZoso-l,2-dicarb-adodecaborane(12). ... 

One of the most important features of a carborane system is its ability to enter into substitution reactions at both the carbon and boron atoms without degradation of the carborane cage. The susceptibility for removal of the most electrophilic boron atom in closed-cage carborane such as 1,2-dicarba-cZoso-dodecaborane is an added advantage for its transformation into open cage form... 

FIGURE 1.5 An effect of dipole moment on hydrophobicity of dicarbadodecaboranes 1,2-dicarba-c/oso-dodecaborane (orf/io-carborane) (1) 1,7-dicarba-c/oso-dodecaborane (mcfa-carborane) (2) 1,12-dicarba-cZoso-dodecaborane (para-carborane) (3). 

FIGURE 6.1 Neutral and anionic boron clusters, o-carborane (1), m-carborane (2), p-carborane (3), nido-o-carborane (4), nido-m-caiborane (5), nido-p-carboiane (6), 1-carbadodecaborate anion (7), dodecahydro-c/oso-dodecaborate anion (8), and decahydro-cZoso-decaborate anion (9). 

In order to solve the problem of the significant toxicity of liposomes prepared from ntdo-carborane lipids 2 and 3, ctoo-dodecaborate has been focused on as an alternative hydrophilic function of boron lipids. BSH is known as a water-soluble divalent c/050-type anion cluster and significantly lowered toxicity (Haritz et al., 1994), and thus has been utilized for clinical treatment of BNCT. Nakamura and coworkers succeeded in the synthesis of double-tailed cZoso-dodecaborate lipids 4a-c and 5a-c, which have a B,2H S-moiety as a hydrophilic function with chirality similar to natural phospholipids, such as distearoylphosphatidylcholine (DSPC), in their lipophilic tails (Lee et al., 2007 Nakamura et al., 2007a). 

Most known polyhedral boron hydrides are decahydro-doi o-decaborate [B,oH,o] , dodeca-hydro-c/oio-dodecaborate [B,2H,2] anions, and dicarba-cZoso-dodecaboranes [C2B,2Hi2] (see Figure 9.1). The first derivatives of [B,oH,o] and [Bi2Hi2] anions were prepared by M. F. Hawthorne, and A. R. Pitochelli [2], and the synthesis and properties of carboranes were first reported at the end of 1963 by chemists from the the Soviet Union and the United States [3,4]. 

J. Abe, N. Nemoto, Y. Nagase, Y. Shirai, T. lyoda, A new class of carborane compounds for second-order nonlinear optics Ab Initio molecular orbital study of hyperpolarizabilities for l-(l ,X -Dicarba-cZoso-dode-caborane-l -yl)-c/o c>-dodecaborate Dianion (X = 2, 7, 12). Inorg. Chem. 1998, 37,172. 

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