Boron halides, reactions

The boron halides are made either by direct reaction of the elements at a high temperature or from boron oxide. The most important is boron trifluoride, BF, an industrial catalyst produced by the reaction between boron oxide, calcium fluoride, and sulfuric acid ... 

Coatings and monolithic components of h-BN are usually produced by CVD by the reaction of a boron halide with ammonia. MOCVD and plasma-CVD are also used. The reaction of boron trichloride and ammonia is as follows ... 

Reaction between boron halides and Grignard reagents... 

This reaction is used with different boron halides and manganese carbonyl derivates in 12 at RT to yield B—Mn compounds (Table 1). 

As an alternative method, poly(cyclodiborazane)s were prepared by the reaction of bis(silylimine)s with chlorodialkylboranes or with methyl dialkylborinates (scheme 18).32 This reaction proceeds via the condensation between V-silylimine and boron halide, eliminating trimethylsilyl halide followed by dimerization. However, the isolated polymer became insoluble after several hours of exposure under air, which resulted from the cross-linking reactions of unreacted trimethylsilyl groups to form trimerized hydrobenzamide derivatives. 

As has already been mentioned, boron halides are electron-deficient molecules. As a result, they tend to act as strong Lewis acids by accepting electron pairs from many types of Lewis bases to form stable acid-base adducts. Electron donors such as ammonia, pyridine, amines, ethers, and many other types of compounds form stable adducts. In behaving as strong Lewis acids, the boron halides act as acid catalysts for several important types of organic reactions (see Chapter 9). 

In addition to functioning as Lewis acids, boron halides undergo many other types of reactions. As is typical of most compounds containing covalent bonds between a nonmetal and a halogen, the boron halides react vigorously with water to yield boric acid and the corresponding hydrogen halide. 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Tetraalkyl-l,6-dihalogeno-2,3,4,5-tetracarba-nido-hexaboranes(6) 56d were obtained in high yield by another route (Scheme 3.2-30), taking advantage of the exchange reactions of the spirotin compounds 57 with boron halides. 

B2H6 from BHg. The simplest reaction observed involves the abstraction of hydride ion from BHi by a boron halide to generate BH3 units which combine to form B2H6. Reaction (16) represents the general reaction observed. 

Bidentate boranes with an o-phenylene backbone constitute some of the simplest examples of polydentate Lewis acids with rigid backbones. They can be prepared by the reaction of boron halides with a 1,2-dimetallated benzene derivative. Thus, the reaction of 1,2-bis(chloromercurio)benzene (5) with boron trichloride affords 1,2-bis(dichloroboryl)benzene (6, Scheme 3). ... 

When the distannyl reagent 7 is employed, the fate of the reaction apparently depends on the reaction conditions. Indeed, Eisch observed that the reaction of 7 with boron trichloride at —40 °C in hydrocarbon solvent is not always selective and leads to the formation of both a monoborylated intermediate (10) that slowly converts into 6 (Scheme 5). The outcome of these reactions is apparently further complicated by a fast methyl group transfer from the tin to the boron centers yielding the undesired monoborylated derivative 11. Eisch also found that such reactions are not limited to the case of boron trialide but can be performed with dialkyl boron halide starting materials. For example, the reaction of the distannane... 

Reactions with halogens give boron halides. While reaction with chlorine can be explosive with diborane, it is slow with bromine. Diborane reacts with alkanes forming alkylboranes. Reactions with aromatics give arylboranes. 

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