Diborane g-

Table 1. Reported values of the bridge dissociation energy of diborane[G)...

A solution of 1.05 M diborane in THF (25 ml, 26 mraol) was added slowly to a stirred suspension of 3-acetyl-5-hydroxy-2-methylindole (1.0 g, 5.3 mmol) in THF (10 ml). After hydrogen evolution ceased, the mixture was heated at reflux for I h, cooled and poured into acetone (75 ml). The mixture was heated briefly to boiling and then evaporated in vacuo. The residue was heated with methanol (50ml) for 20min. The solution was concentrated and 3NHC1 (40ml) was added. The mixture was extracted with ether and the extracts dried (MgSO ) and evaporated to yield a yellow oil. Vacuum sublimation or recrystallization yielded pure product (0.76 g, 82%). 

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. 

Boron Hydrides" under "Boron Compounds" in ECT 1st ed., Vol. 2, pp. 593—600, by S. H. Bauer, Cornell University "Boron Hydrides and Related Compounds" under "Boron Compounds," Suppl. 1, pp. 103—130, by S. H. Bauer, Cornell University "Diborane and Higher Boron Hydrides" under "Boron Compounds," Suppl. 2, pp. 109—113, by W. J. Shepherd and E. B. Ayres, Gallery Chemical Company "Boron Hydrides" under "Boron Compounds" in ECT 2nd ed., Vol. 3, pp. 684—706, by G. W. Campbell, Jr., U.S. Borax Research Corporation "Boron Hydrides and their MetaHo Derivatives" under "Boron Compounds," in ECT 3rd ed., Vol. 4, pp. 135—183, by R. W. Rudolph, The University of Michigan. 

A solution of cholest-4-en-3-one (139), 1 g, in diethylene glycol dimethyl ether (20 ml) is treated for 1 hr with a large excess of diborane at room temperature under nitrogen and then left for a further 40 min. Acetic anhydride (10 ml) is added and the solution refluxed for 1 hr. The mixture is concentrated to a small volume, diluted with water and extracted with ether. The extracts are washed with 10% sodium hydroxide solution, then with water and dried over sodium sulfate. Removal of the solvent leaves a brown oil (1.06 g) which is purified by chromatography on alumina (activity I). Hexane elutes the title compound (141), 0.68 g mp 76-77°. Successive crystallization from acetone-methanol yields material mp 78-79°, [a]p 66°. 

Cluster expansion reactions with diborane provide an alternative route to intermediate closo-carboranes, e.g. ... 

X = alkyl, H, halogen, etc. They are usually colourless, crystalline compounds with mp in the range 0-100° for X = H and 50-200° for X = halogen. Synthetic routes, and factors affecting the stability of the adducts have already been discussed (p. 165 and p. 198). In cases where diborane undergoes unsymmetrical cleavage (e.g. with NH3) alternative routes must be devised ... 

Free borane (2) exists as gaseous dimer—the diborane BaHg. In addition Lewis acid/Lewis base-complexes, as for example formed in an ethereal solvent, e.g. 4, are commercially available ... 

A solution of 28.2 g (0.30 mole) of norbornene in 100 ml of THF is placed in the flask. The gas dispersion tube is immersed in the reaction liquid and connected with Tygon tubing to a 250-ml three-necked flask serving as the diborane generator. 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

F) 9 g of the diketo-pyrazino-morphanthridine compound obtained above are reduced with diborane to give mianserin. 

To 78 ml of a 1 M solution of diborane in tetrahydrofuran under nitrogen and cooled to 0°C is added dropwise over a period of 40 minutes 13.5 g of N-tert-butyl-2-(5-benzyloxy-6-hy-... 

H.12 The reaction of boron trifluoride, BF,(g), with sodium borohydride, NaBH4(s), leads to the formation of sodium tetrafluoroborate, NaBF4(s), and diborane gas, B2Hfc(g). The diborane reacts with the oxygen in air, forming boron oxide, B20 j(s), and water. Write the two balanced equations leading to the formation of boron oxide. 

X 14.111 (a) Examine the structures of diborane, B2H6, and AI2CI6(g), which can be found on the Web site for this book. Compare the bonding in these two je compounds. How are they similar (b) What are the differences, if any, in the types of bonds formed (c) What is the hybridization of the Group 13/III element (d) Are the molecules planar If not, describe their shapes. 

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