Decaborane

In most of the other investigations of boron hydride pyrolysis no kinetic data are reported usually only the reaction products and in some cases also active intermediates are detailed. For these studies the reader is referred to existing literature reviews81,85. 

This survey has shown that the homogeneous decomposition of hydrides of the elements becomes more complex when moving from right to left in the main 

The temperatures of measurable decay range from room temperature for tetraborane to several thousand degrees for water. While the reactions at high temperature are real dissociations to smaller particles, the decomposition occurring at lower temperatures are generally condensations with the simultaneous formation of hydrogen. In the latter case the possibilities for the initial and subsequent elementary steps increase enormously. In these cases it is extremely difficult to obtain the rate of the initial step and even harder to describe the overall reaction in terms of the kinetics of the single steps. 

In some cases where the gas-phase decomposition has been studied by classical methods using static systems the question of the degree of homogeneity of the reactions is unsolved. 

Although the main purpose of this chapter is to provide a critical review of the field, we hope that it will also stimulate future work. 

---

Other boron hydrides are known, most of them having the general formula B H + 4- for example pentaborane, B5H9, decaborane, BjqHi4. Each can be made by heating diborane in suitable conditions for example at 420 K, decaborane is obtained. Boron hydrides have been tried as rocket fuels. 

Examples BjHg, diborane Bj(,Hj4, decaborane(14) BjqHjj, decaborane(16) P2H4, diphos-phane SnjHg, distannane HjSej, diselane HjTej, ditellane H2S5, pentasulfane and PbH4, plum-... 

G in the presence of a catalytic amount of a Lewis base such as dimethylether, (GH2)20. In addition to the gas-phase pyrolysis of diborane, can be prepared by a solution-phase process developed at Union Garbide Gorp. Decaborane is a key intermediate in the preparation of many carboranes and metaHa derivatives. As of this writing, this important compound is not manufactured on a large scale in the western world and is in short supply. Prices for decaborane in 1991 were up to 10,000/kg. 

Except for a more detailed consideration of the interaction of donor ligands with boranes is beyond the scope of this review. Decaborane is... 

B2qH240H] anion (75). Both B2QH24OH2 and [B2qH240H] are isoelectronic with the [B qH ] anion (77). The hydropolyborate ions formed by proton abstraction from decaborane are usehil intermediates for the preparation of metaHaboranes and heteroboranes. 

The base-promoted closure of decaborane(14) yields salts of the [B qH q] anion (eq. 34). Relatively strong Lewis bases, such as trialkylamines, are required to accomplish this reaction as weaker bases, such as diethylsulfide and acetonitrile, form stable 6,9-L2B2qH22 species where L = (C2H )2S, H CCN, etc (90). 

The related mono-A/-alkylated carboranes, 7-(NH2R)-7-CB2qH22, can be prepared by treatment of decaborane(14) with alkyl isocyanides (125). 

The silacarborane analogue of C,C-dimethyl-o / o-carborane, closo-l]l-((C i]) -l]lSi[ fri [128270 8 ] h.3.s been reported (179). This o-sdacarborane, which has an icosahedral framework much like o-carborane and is reported to be stable to air and moisture, was obtained in low yield from the reaction of decaborane and bis (dimethyl amino)metbyl silane in refluxing benzene. 

Polyhedral Boron Hydrides. Although relatively large quantities of polyhedral boron hydrides and carboranes have been produced under various government contracts, these materials are not currendy produced on a regular commercial basis. Pentaborane(9) nido- and decaborane(14) and carboranes, such as the ortho and meta-carboranes closo-1 1 well as various other derivatives, are... 

Dead Sea Bromine Group, 177 Dead Sea Magnesium Ltd., 177 Decaborane, 49 Decabromodiphenyl ether, 49 DECP, 50... 

The cyclobutadiene analogue diazadiboretidine reacts with hexafluoroacetone to give a nng expansion product [776] (equation 90) 6-(3-Fluoroaryl)decaborane is formed by alkylation of decaboranyl anion and separation of the two isomers (5- and 6-benzyl) formed by reaction with dimethyl sulfide [777] (equation 91). 

Decaborane is the most studied of all the polyhedral boranes and at one time (mid-1950s) was manufactured on a multitonne scale in the USA as a potential high-energy fuel. It is now obtainable in research quantities by the pyrolysis of B2H9 at 100-200°C in the presence of catalytic amounts of Lewis bases such as Me20. B10H14 is a colourless, volatile, crystalline solid (see Table 6.2, p. 163) which... 

The stability of the phosphine adducts is notable as is the fact that thioethers readily form such adducts whereas ethers do not. Bis-ligand adducts of moderate stability play an important role in activating decaborane for several types of reaction to be considered in moie detail in subsequent paragraphs, e.g. ... 

Plane projection of the slructure or/ B gH2]. The two decaborane units are fused at the S(7 > and 6(6 ) positions to give a non rTJmetric structure with Cj symmetry... 

---