Decaborane complexes

Boron forms a remarkable series of binary compounds with hydrogen—the boranes. These compounds include diborane, B2H6, and more complex compounds such as decaborane, B10H14. Anionic versions of these compounds, the borohydrides, are known the most important is BH4 as sodium borohydride, NaBH4. 

This sequence of reactions is a useful route to the pure element, but more complex boranes form when the heating is less severe. When diborane is heated to 100°C, for instance, it forms decaborane, B]0H14, a solid that melts at 100°C. Decaborane is stable in air, is oxidized by water only slowly, and is an example of the general rule that heavier boranes are less flammable than boranes of low molar mass. 

The literature3 contains some limited work on decaborane-based polymer systems. Typically, most utilize the Lewis acid/base reaction between decaborane (Lewis acid, B10H12) and amines and phosphines (Lewis bases, L) resulting in the formation of complexes (see scheme 2) having the general formulas B10H12L2. For example, the... 

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). 

Figure 13 CpFe complexes with phosphacarba-n/do-decaborane phosphadicarba-n/tfo-undecaborane.

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

Decaborane dianion, oxidative coupling, 26 73 Decaboron decahalides, 26 13, 48 hydrogenation of chloride, 26 48 pyrolysis of dianions, 26 48 Decabromotriselenate(lI,IV), 35 290 Decadiene complexes with silver, 12 340 Decaholotellurate(IV), structure, 35 249-251 Decarbonylation, thermal, of trifluoroacetyl derivatives, 27 295-300... 

The structures of some ethylated derivs of penta-borane and decaborane are reported by Williams(Ref 34). Stock Pohland(Ref 2) reported the formation of complexes by the reaction of NH3 with boranes. The structure props of these boron hydride ammo-niates were studied by Agronomov(Ref 7)... 

The open faces in 23 or in 25 invite for adding transition metal fragments. This has been carried out successfully in the case of 23 by adding two Fe(CO)j units (Scheme 6).23 The complex 26 has the same electron count as nidb-decaborane(14) and its structural features, as determined by X-ray analysis, are similar. Work is in progress to make use of the two open faces in 25. 

Most compounds have neutral (group VA or VIA) ligands bonded to Cu, but CuClj and [Bj Hij] yield the complex, (Et4N)j(Cl2CuBjgH,3). With [B,H, ], [BgHjjSj- and [BjjH, ] only ionic tetrakis(triphenylphosphine)Cu and -Ag salts are isolated. The decaborane CUjjBipHjp is also prepared by ... 

Hydroboration is faster than cleavage with borane, but H2BCI etherate cleaves unsaturated acetals without giving hydroboration (equation 10). Lower yields are obtained with the less reactive Me2S complex, but that reagent gives good yields of dihydroxy diethers from chiral bisacetals (equation 11). The diethyl acetal of benzaldehyde can be reduced to ethyl benzyl ether in moderate yield by decaborane in toluene at 120-130 C (equation 12). °... 

Heating B2H6 above 100°C leads to pyrolysis and generates a variety of more complex boranes of which tetraborane(lO) B4H10 and decaborane( 14) B1QH14 are the most stable. Other reactions can... 

In many catalytic processes and transition metal mediated reactions, a-bor-ane complexes have been shown to be intermediates. The bis(borane) complex Cp2Ti( 72-HBcat/)2 (HBcaT = HBcat-4-f-Bu) is a highly active catalyst for the hydroboration of vinylarenes [37]. A mechanism, shown in Scheme 3, has been proposed for the Ti-catalyzed hydroboration on the basis of a detailed mechanistic study [37]. Theoretical calculations provided further support to the proposed reaction mechanism and showed that the reductive elimination step, giving the product molecules, is rate-determining [38]. In the Cp2Ti(CO)2 catalyzed hydroboration of alkynes [36,37], the proposed reaction mechanism (Scheme 4) also involves a a-borane complex similar to 11 and 14. In the titanium-catalyzed decaborane-olefin hydroborations [47,48], a-borane complexes were also considered as intermediates. In the Cp2MH (M = Nb, Ta) mediated hydroboration reactions of olefins [39,41], Smith and his coworkers observed several interesting cr-borane complexes, such as 21-23 discussed above. 

The B spectra of some 1,10-disubstituted decaborane derivatives have been discussed by Knoth. A high field doublet is usually found for the equatorial boron atoms and a broad singlet at low field due to the apical boron atoms. Several octachloro-derivatives (l,10-BioClgX2) are also discussed by these authors. The B chemical shifts of some complexes of decaborane of the form B oHi2L2 have been tabulateda generalization was made that the doublet arising... 

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