Diborane decomposition

The experimental data of Bragg et ah88 on diborane decomposition, like those of previous investigators, have been interpreted in terms of a mechanism involving monoborane (BH3) as a reactive intermediate. Fehlner92 proposed that a different mechanism based on the initial dissociation reaction... 

As might be expected, the principal product of diborane decomposition with Y iiation from Co (97) is the same as with ultraviolet light. At a few per cent decomposition, B Hio and only a trace of higher boranes are obtained. 

Silane, pure or doped, is used to prepare semiconducting siUcon by thermal decomposition at >600° C. Gaseous dopants such as germane, arsine, or diborane maybe added to the silane at very low concentrations in the epitaxial growing of semiconducting siUcon for the electronics industry. Higher silanes, eg, Si H and Si Hg, are known but are less stable than SiH. These are analogues of lower saturated hydrocarbons. 

Hydroboration affords an efficient preparation of the 5a-A -system (141, for example) from A" -3-ketones. Reaction with diborane followed by decomposition of the organoboron intermediate with refluxing acetic anhydride gives good yields of olefins. Ketones must be protected, and alcohols are transformed to acetates. A -7-Ketones yield 5oc-A -olefins (for example, 138). 

Olefins may be obtained by elimination from the organoboron intermediates formed from enol derivatives and diborane. " As in the reaction with a,jS-unsaturated ketones (section IX), the conversion is carried out in two parts first formation of the diborane adduct and second, decomposition in refluxing acetic anhydride. 

These methods deal with specific cases. The list of examples is not exhaustive. The low-T (200-300°C) decomposition of the transition-metal borohydrides M(BH4> , e.g., leads to titanium, zirconium, halfnium, uranium and thorium borides . Alternatively, the uranium diboride may be obtained by reacting uranium hydride with diborane in hydrogen at 200-400°C. 

It was shown that the rate of decomposition of diborane follows a rate law that corresponds to d(B2H6) = k B2H(, 2. This is consistent with the dissociation of diborane into BH3 as the rate determining step with formation of B3H9. This intermediate then decomposes with hydrogen evolution to give unstable B3H7 which on reaction with further BH3 produces B4H10 as the first isolable poly-borane ... 

B4H10 forms slowly by decomposition of diborane, B2H6, in a slightly exothermic reaction (AH = -14 kj mol 1) and it is produced in a hot-cold-reactor (120 °C/ -78 °C). At present the best method is to react Bu4N[B3H8] with BC13 or A1C13 in the presence of toluene as shown in Eq. (26) ... 

Interest in the photochemistry of boron compounds dates back as far as 1913 when Alfred Stock investigated the effects of light from a mercury vapor lamp on diboran 6) and on tetraboran 10). In the case of diborane(6) he commented UV light will also decompose B2H6. The volume of a sample in a quartz tube increased by 1/6 after 24 hours exposure to a mercury-arc lamp, and a pale yellow crystalline substance appeared. Stock also observed that B4H q decomposition to B2H is not noticeably influenced by sunlight. 

F) K.K. Andreev, "Termicheskoye Razlo-zheniye i Goreniye Vzryvchatykh Veshchestv (Thermal Decomposition and Combustion of Explosive Substances), GosEnergoIzdat, Moscow(1957) G) P. Breisacher et al, "Flame Front Structure of Lean Diborane-Air and Diborane-Hydrocarbon-Air Mixtures", 7thSympCombstn(1959), PP 894-902 H) M. Getstein, "A Study of Alkylsilane Flames , Ibid, pp 903-05 I) P.L. Harrison, "The Combustion.of Titanium and Zirconium , Ibid, pp 913-20 J) J.D. Lewis A.C, Merrington, "Combustion of n-Heptane Spray in the Decomposition Products of Concentrated Hydrogen Peroxide , Ibid, pp 953-57... 

Borazine, B3N3H6, was first prepared by thermolysis of the diborane ammonia adduct [(BH2)(NH3)2] [BH4] . More convenient procedures for the laboratory preparation of this important ring system in multigram quantities involve either (a) the decomposition of ammonia- borane [eqn (9.1)] or (b) the reaction between ammonium sulfate and sodium borohydride [eqn (9.2)]. The latter method provides a convenient and economical synthesis of borazine. 

All of the compounds discussed thus far (except diborane and decaborane) contain only two-center, two-electron bonds. A ample boron hydride containing three types of bonds is tetraborane, B4H 0 (Fig. 16.43). it is formed by the slow decomposition of diborane ... 

There, are at least six definitely characterized boron hydrides, as follows diborane(6), B H tetraborane(lO), B4 H, pentaborane(9) (stable), B3 H pentaborane( 11) (unstable). B5 Hu hexaborane(lO). H10 and decaborane(14). Bio H14. In these names, note that the prefix denotes the number of boron atoms, while the figure in parentheses denotes the number of hydrogen atoms. In addition to these compounds, which are all gases or volatile liquids except decaborane(L4), decomposition of the lower boron hydrides yields colorless or yellow solid boron hydrides, ranging in composition from (BItysty to (BII). This readiness to polymerize is evidence of the reactivity of these borane compounds, which readily form additional products with ammonia, with the amalgams of the active metals, and with many otganic compounds, as well as with CO. 

Tetrakis(acetato)di- U-amido-diborane is a white crystalline compound which is not too sensitive to moisture. It can be stored in a nitrogen atmosphere in a refrigerator for long periods without decomposition. It is sparingly soluble in most organic solvents and slowly dissolves in glacial acetic acid and acetic anhydride. Monoclinic and triclinic crystalline forms were obtained by recrystallization from acetic anhydride and glacial acetic acid, respectively.1 The infrared spectrum recorded (Beckman i.r.-12) by the KBr pellet technique contains major absorption bands (at frequencies cm.-1) 3280(s), 3230(s), 3100(s), 1740(w,sh),... 

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