Structure carborane

Hosmane, N. S., Zh. Yinghuai, J. A. Maguire, W. Kaim, and M. Takagaki. 2009. Nano and dendritic structured carboranes and metaUacarboranes From materials to cancer therapy. J. Organomet. Chem. 694 1690-1697. 

Substantial improvements in the heat-resisting capability of silicone rubbers were achieved with the appearance of the poly(carborane siloxanes). First described in 1966, they were introduced commercially by the Olin Corporation in 1971 as Dexsil. The polymers have the essential structure... 

Carboranes (or more correctly carbaboranes) are compounds having as the basic structural unit a number of C and B atoms arranged on... 

R. E. Williams, Coordination number-pattern recognition theory of carborane structures, Adv. Incrg. Chem. Radiochem. 18, 67-142 (1976). R. E. Williams, Chap. 2 in G. A. Olah, K. Wade and R. E. Williams (eds.). Electron Deficient Boron and Carbon Clusters, Wiley, New York, 1991, pp. 11-93. 

Figure 6.21 Relation between C2B9Hn and C sHs". In this formalism the c/o.ro-carboranes C2B10H12 are considered as a coordination complex between the pentahapto 6-electron donor C2B9H] - and the acceptor BH (which has 3 vacant orbitals). The o/oso-structure can be regained by capping the open pentagonal face with an equivalent metal acceptor that has 3 vacant orbitals.

The structure of the bimetallic 10-vertex cluster was shown by X-ray diffraction to be (84). When the icosahedral carborane l,2-C2BioHi2 was used, the reaction led to the first supraicosahedral metallocarboranes with 13- and 14-vertex polyhedral structures (85)-(89). Facile isomerism of the 13-vertex monometallodicarbaboranes was observed as indicated in the scheme above (in which = CH and O = BH). 

C = 12 internationally adopted as the unified atomic weight standard by both chemi.sts and physicists. 6-coordinate carbon established in various carboranes by W. N. Lipscomb and others. (Nobel Prize 1976 for structure and bonding of boranes). 

To conclude, we shall mention some metal-atom reactions with boranes (172) and carboranes (173). When cobalt atoms reacted with pentaboraneO) and cyclopentadiene, a number of new metalloborane clusters were formed (172), two of which were 65115003(17-05115)3 and cyclopentyl-B5H40o2(i7-05H5)3. Possible structures for the former are shown in Fig. 42. The reaction of cyclopentadiene, pentaboraneO), and 2-butyne with cobalt atoms yielded the metallocarborane species illustrated in Fig. 43 (173). 

Coordination Number Pattern Recognition Theory of Carborane Structures Robert E. Williams... 

Some group-IB and -IIB boranes or carboranes, especially of Cu, possess M — H—B structure units and are not discussed here because no direct metal-boron bond exists. 

The structure of the disilanol l,7-bis[hydroxy(dimethyl)silylmethyl]-m-carborane has a hydrogen-bonded network reminiscent of the sil-oxanediol type shown in Fig. 10c, in which pairs of molecules are hydrogen-bonded together and then these pairs are further linked to give a double chain (290). 

But the discovery of the carboranes in the early 1960s revealed that bonding possibilities other than simple o-- or 7r-bonds between B and C centers were necessary to understand the structure of such compounds as 1,5-dicarba-closo-pentaborane(5) [6 in Eq. (1)], which is obtained in low yield in an electrical discharge.6 Ordinary valence conventions cannot account for the bonding of boron to five other atoms, and hence the concept of electron-deficient bonding must be invoked for boron. Although carbon seems to adhere to normal tetravalence, again it should be remembered... 

Quite a number of silylnickel and silylenenickel compounds have been reported, and only a few can be cited here2305-2309 Bis(silyl)nickel complexes have been implicated as important intermediates in Ni-catalyzed double silylation of various organic substrates. Using an o-bis(dimethylsilyl)carborane ligand, complex (930) could be isolated and structurally characterized 2310 Its unusual thermal stability is attributed to the advantageous steric and electronic properties of the carboranyl unit. (930) undergoes... 

Hawthorne and co-workers have also produced a series of macrocyclic Lewis acid hosts called mercuracarborands (156, 157, and 158) (Fig. 84) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. They were synthesized by a kinetic halide ion template effect that afforded tetrameric cycles or cyclic trimers in the presence or absence of halide ion templates, respectively.163 These complexes, which can bind a variety of electron-rich guests, are ideal for catalytic and ion-sensing applications, as well as for the assembly of supramolecular architectures. 

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