Boron subhalides

See also Borates Boric acid Sodium borates boron oxides, 4 246-249 boron oxides table,4 242t environmental concerns, 4 284—285 health and safety factors, 4 285-288 occurrence, 4 245—246 Boron perchlorates, 18 278 Boron phosphate, 4 242t, 283 Boron removal, from water, 14 418 Boron-stabilized carbanions, 13 660-661 Boron subhalides, 4 141 Boron suboxide, 4 242t Boron tribromide, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t, 325 reactions, 4 141 specifications, 4 147t uses of, 4 149 Boron trichloride, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t reactions, 4 141... 

Boron subhalides are binary compounds of boron and the halogens, where the atomic ratio of halogen to boron is less than 3. The boron monohalides, BC1, [20583-55-5], bromoborane(l) [19961-29-6], BBr, and iodoborane(l) [13842-56-3], BI, are unstable species that have been observed spectroscopically when the respective trihalides were subjected to a discharge (5). Boron dihalide radicals have been studied, and structural and thermochemical data for these species ( BX2) have been deduced (5). 

Rednction of boron trihaUdes to elemental boron can be accomplished by heating with alkali metals, alkaline earth metals, or hydrogen. Under the proper conditions, rednctions of this type can also yield diborane and, under selected conditions, boron subhalides (see below). Metal hydrides also react with boron trihalides to give diborane. Boron nitride and boron carbide have been prepared by the high-temperature reductions of boron trihalides with ammonia and methane, respectively, and deposited on metal substrates by CVD. 

Diboron tetrachlorides undergo a variety of reactions, including facile additions to aUcenes similar to hydroboration (equation 20). The reactions of boron subhalides, particularly B2CI4, with organic and organometallic compounds, have been studied in some detail. 

Group 13 clusters with electron counts less than the 2n - - 2 electrons corresponding to closo deltahedra have also been described. The classic examples of these are the boron subhalides, B C1 where n = 4, 8 -12 (and a more limited set of bromides and iodides), which have an electron count of 2n and are known as hypercloso clusters. These are based on the same closo structures expected for the 2n - - 2 electron clusters, namely, tetrahedral, dodecahedral, and tricapped trigonal prismatic for n = 4, 8, and 9. The 2n - - 2 dianions B C1 also show the expected deltahedral structures. The stability of the B C1 clusters has been attributed to a combination of the r-donor properties of the halides and steric effects. ... 

Studies of the general chemistry of compounds containing the B—B linkage have been reviewed (IJ, 56). The boron subhalides have also been discussed at some length in general reviews of boron halide chemistry (67, 101). 

Similar reactions occur between boron subhalides and a number of chloro- and bromoolefins. The halogen originally present in the olefin appears, in differing amounts, as boron-bonded halogen in the addition product and as boron trihalide. 

Boron Halides.— Timms has published a short review on the preparation and properties of boron subhalides. ... 

D. Saulys and J. A. Morrison, Inorg. Chem., 1980, 19, 3057. Boron subhalide chemistry. Formation of octabromomethylnonaborane, CHsBgBrs, and other alkylated nonaboranes from triethylammonium decabromodecaborate. 

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