Silicon boron hydrides

The reaction of HCl and silicon, germanium, and boron hydrides is cataly2ed by aluminum chloride and is useful for preparing chloro-substituted silanes andgermanes. 

Boron creates an electron deficiency in the silicon lattice resulting in ay>-type semiconductor forp—n junctions. Boron compounds are more commonly used as the dopant, however (see Boron HYDRIDES). 

Diborane(6), B2H6. This spontaneously flammable gas is consumed primarily by the dectronics industry as a dopant in the production of silicon wafers for use in semiconductors. It is also used to produce amine boranes and the higher boron hydrides. Callery Chemical Co., a division of Mine Safety Appliances Co., and Voltaix, Inc., are the main U.S. producers of this substance. Several hundred thousand pounds were manufactured worldwide in 1990. 

Borides Carbon boride, CB6. and silicon borides SiB3 and SiB6 are hard, crystalline solids, produced in ihe electric furnace magnesium boride, Mgi B2, brown solid, by reaction of boron oxide and magnesium powder ignited, forms boron hydrides with HC1 calcium boride, Ca3 B2, forms boron hydrides and hydrogen gas with IIC1. 

But carbon is not unique in forming bonds to itself because other elements such as boron, silicon, and phosphorus form strong bonds in the elementary state. The uniqueness of carbon stems more from the fact that it forms strong carbon-carbon bonds that also are strong when in combination with other elements. For example, the combination of hydrogen with carbon affords a remarkable variety of carbon hydrides, or hydrocarbons as they usually are called. In contrast, none of the other second-row elements except boron gives a very extensive system of stable hydrides, and most of the boron hydrides are much more reactive than hydrocarbons, especially to water and air. 

Stock, A., 1964, Hydrides of Boron and Silicon, Cornell University Press, Ithaca, N.Y. In connection with this presentation of his pioneering research on boron hydrides, Stock describes the chemical vacuum line techniques which he invented. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Some preliminary information is also available on the reactions of S( D) atoms with silicon and boron hydrides. 

In summary, myriad boron hydride and silicon hydride reduction methods are available for the reduction of indoles to indolines. It is interesting to compare the various methods for the stereoselective reduction of 2,3-dimethylindole to cis- and trfl/is-2,3-dimethylindoline (Table 1). While most methods show a preference for the more stable trans isomer, only with Zn(BH4>2 is this preference pronounced. 

The method seems to offer promise of alkylating certain boron hydrides (compare 126). In addition, hydrides of tin and silicon seem to undergo an analogous reaction. Thus it has been observed that triphenyltin hydride reacts with methyllithium to yield mainly lithium hydride and triphenyl-methyltin (50). 

In 1912 Alfred Stock (1876-1946) developed techniques to explore two new series of exotic compounds silicon hydrides and boron hydrides. The latter were synthesized as a mixture through reaction of magnesium boride with hydrogen chloride as shown below (not balanced). 

But organic chemistry has also benefitted from the exploration of (some would say takeover bid for) the rest of the periodic table. The organic chemistry of silicon, boron, lithium, tin, copper, zinc, and palladium has been particularly well studied and these elements are common constituents of organic reagents used in the laboratory. You will meet many of them throughout this book. Butyllithium, trimethylsilyl chloride, tributyltin hydride, diethylzinc, and lithium dimethylcuprate provide examples. 

The hydrides of B and Si are volatile and flammable compounds. The boranes, as the boron hydrides are termed, form many interesting hydrogen-bridged structures that are seldom observed with other main group elements. Both boron and silicon form numerous and complex oxygen-containing structures knovm as the borates... 

Why did I decide to undertake my doctorate research in the exotic field of boron hydrides As it happened, my girlfriend, Sarah Baylen, soon to become my wife, presented me with a graduation gift, Alfred Stock s book. The Hydrides of Boron and Silicon. / read this book and became interested in the subject. How did it happen that she selected this particular book This was the time of the Depression. None of us had much money. It appears she selected as her gift the most economical chemistry book ( 2.06) available in the University of Chicago bookstore. Such are the developments that can shape a career. 

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