Amines boron hydrides

Despite the fact that many boron hydride compounds possess unique chemical and physical properties, very few of these compounds have yet undergone significant commercial exploitation. This is largely owing to the extremely high cost of most boron hydride materials, which has discouraged development of all but the most exotic appHcations. Nevertheless, considerable commercial potential is foreseen for boron hydride materials if and when economical and rehable sources become available. Only the simplest of boron hydride compounds, most notably sodium tetrahydroborate, NajBHJ, diborane(6), B2H, and some of the borane adducts, eg, amine boranes, are now produced in significant commercial quantities. 

Diborane(6), B2H. This spontaneously flammable gas is consumed primarily by the electronics industry as a dopant in the production of siHcon wafers for use in semiconductors. It is also used to produce amine boranes and the higher boron hydrides. Gallery Chemical Co., a division of Mine Safety AppHances Co., and Voltaix, Inc., are the main U.S. producers of this substance. Several hundred thousand pounds were manufactured worldwide in 1990. 

Sodium borobydride reacts with Lewis acids in nonprotic solvents to yield diborane [19287-45-7] 2 6 which can then be used to generate other useful organoboranes such as amine boranes, alkyl boranes, and boron hydride clusters. 

Enantioselective reduction of ketoxime ethers with chiral boron hydrides produces chiral 0-alkylhydroxylamines with variable ee. Reduction of oxime ethers of type 94 (equation 65) with norephedrine-derived oxazoborolidine 95 proceeds with very high ee. However, an analogous reduction of acyclic aromatic oximes with chiral oxab-orazolidines produced a mixture of amine and hydroxylamine . 

A qualitatively similar dependence of ADh on boron orbital hybridization is noted in boron hydrides (104). -1bh = 81 cps for BHr where boron is tetrahedral while ABH = 136 cps for borazole where boron presumably is sp2. A ijh for BH3 adducts with ethers, amines, and phosphines range between 90 and 103 cps and for these compounds boron quadrupole coupling constants have been interpreted (22) in terms of a boron hybridization intermediate between sp2 and sp2. However, the simple dependence of... 

Aminoboronhydride Compounds. Many amino-boronhydride compds and their derivatives are volatile and self-inflammable. A series of papers by H.I.Schlesinger et al published in JACS on boron hydrides(qv) include the prepn and props of the following amino-boronhydrides and their derivatives borine-amine, H,N BH, or BHSN dimethylamino-borine(or dimethylaminoboric add) (CH,)2 BNHa dimethylamioodiborane(CH,)2NB2Hs bor-inetriamine B,N,Hg borinetrimethylene (CHJ,NBH aminodiborane HaN BaH, or BjHjN methylaminodiborane CH,HN "... 

As a result of the hydridic nature of the hydrogen attached to boron, amine-boranes are interesting and useful reducing agents and have been employed in the reduction of numerous organic carbonyl compounds. They have been utilized in studying the kinetics and mechanism of hydride reactions and are precursors for the synthesis of substituted boranes, borazines, boronium ions, higher boron hydrides, and carboranes. 

Asymmetric reduction of (5s)-sulfmimine 110 with diisobutylaluminum hydride (DIBAL) afforded a diastereomeric mixture of sulfinamides 111 in 92% yield and in a ratio of 96 4.34 Use of sodium boron hydride, lithium aluminum hydride, or lithium alkoxyaluminum hydride resulted in lower optical yields.33,34,75 The sul-finyl group can be removed by treating 111 with trifluoroacetic acid (TFA) and methanol to give a-phenylethyl amine (112). 

The modification of aluminum or boron hydrides with chiral protic substances, such as R OH or RR NH, generates useful reagents for the asymmetric reduction of prochiral ketones or imines leading to optically active secondary alcohols and amines, respectively. Some reviews have appearered in the literature. ... 

The tri-2-phenylpropylborane formed can be oxidized and hydrolyzed to 2-phenylpropanol-l, thus representing [as with aluminum alkyls (146)] an overall anti-Markownikoff hydration of a-olefins. Besides employing trialkylboranes as a source of boron hydrides, similar additions have been accomplished by heating olefins with boron hydride-amine complexes. As the latter are not as oxygen-sensitive, they are easier to handle (73) ... 

Discovery of the diammoniate of diborane (B2He, 2NH3) and bor-azene (B3N3H6), better known by its older name of borazole, by Stock (131) indicated that the boron hydrides could be used to prepare interesting boron-nitrogen compounds. This approach to boron chemistry was rapidly extended when the principles discussed in the preceding section were clearly recognized. Thus the compound (CH3)3N BH3, the first borane adduct to be characterized (39), pointed the way to the synthesis of a number of similar substances directly from diborane and amines for exam-... 

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