Amine-boranes

Amine antioxidants Amine boranes Amine Guard... 

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. 

Amine Boranes. Trialkylamine and dialkylamine boranes, such as tri-Z-butylamine borane and dimethylamine borane, are mainly used in... 

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. 

Borane complexes are the most widely used commercial boron compounds, after sodium borobydride. Examples used in organic synthesis are amine borane complexes and borane complexes of tetrahydrofuran and dimethyl sulfide. 

Amine—borane adducts have the general formula R3N BX where R = H, alkyl, etc, and X = alkyl, H, halogen, etc. These compounds, characterized by a coordinate covalent bond between boron and nitrogen, form a class of reducing agents having a broad spectmm of reduction potentials (5). 

Dimethyl amine borane [74-94-2] important as a reducing agent in electroless plating (qv) (8), can be synthesized as shown in equation 2 (9). 

The synthesis of a number of other amine—borane complexes from THF BH [14044-65-6] have also been described (10). 

Using a procedure similar to the synthesis of amine boranes, a series of amine cyanoboranes where the amine = (CH3)3N, (CH3)2NH, (CH3)NH2, C3H3N, or (CgH3)NH2 have been prepared as shown in equation 4 (11). 

Compounds of the type LBH2X can be prepared by the reaction of the appropriate amine borane and hydrogen haHdes or halogens. The synthesis of the trimethyl amine iodoborane [25741-81-5] adduct (eq. 8) yields a precursor for the preparation of the trimethyl amine isocyanoborane [60045-36-5] adduct as shown in equation 9 (15). 

Properties and Reactions. Amine boranes are usually colodess, crystalline compounds, which exhibit sharp melting points and thermal stability when pure. Primary and secondary amine boranes are generally soHds at ambient temperatures. With the exception of trimetbylamine borane, the ahphatic /-amine boranes are Hquids. The nature of the bonding in amine boranes has been the subject of theoretical investigations (21—23). 

Experimental results are consistent with this representation nucleophilic reagents always attack B in amine—borane complexes, electrophilic reagents preferentially attack N. 

Amine boranes have been examined by a variety of spectroscopic methods (24—29). The boron-substituted alpha-amino acids have been utilized in animal model studies. These compounds along with their precursors and selected derivatives have been shown to possess antineoplastic, antiarthritic, and hypolipidemic activity (30—32). The boron amino acid analogues are also being evaluated for possible utility in boron neutron capture therapy (BNCT) (33). 

The influence of boron-bonded ligands on the kinetics and mechanistic pathways of hydrolysis of amine boranes has been examined (37,38). The stoichiometry of trimetbyl amine azidoborane [61652-29-7] hydrolysis in acidic solution is given in equation 10. It is suggested that protonation occurs at the azide ligand enabling its departure as the relatively labile HN species. 

The reaction between a trinuclear metal carbonyl cluster and trimetbyl amine borane has been investigated (41) and here the cluster anion functions as a Lewis base toward the boron atom, forming a B—O covalent bond (see Carbonyls). Molecular orbital calculations, supported by stmctural characterization, show that coordination of the amine borane causes small changes in the trinuclear framework. 

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

A more convenient high-yield synthesis of Bi2Hi2 is by the direct reaction of amine-boranes with BiqHu in the absence of solvents ... 

Amine-borane adducts have the general formula R3NBX3 where R = alkyl, H, etc., and... 

The nature of the bonding in amine-boranes and related adducts has been the subject of considerable theoretical discussion and has also been the source of some confusion. Conventional representations of the donor-... 

Amin-Borane haben gegeniiber den komplexen Borhydriden den Vorteil, daB sie neben Wasser auch in den meisten organischen Losungsmitteln loslich und nur wenig saureemp-findlich sind. 

AUgemein werden Amin-Borane durch Umsetzung von Amin-Hydrochloriden mit Alkalimetall-oder Erdal-kalimetall-boranat hergestellt2 ... 

Benzoxazole reagieren mit Diboran in 1,2-Dimethoxy-athan bei 25° unter Amin-Boran-Bildung, nachfolgender Umlagerung und Verseifung der 2,3-Dihydro-(benzo-1,3,2-oxazaborole), mit Salzsaure zu den entsprechenden o-Amino-phenolen2 ... 

Bei der Reduktion mit Diboran verbrauchen unsubstituierte Carbonsaure-amide sie-ben, monosubstituierte sechs und disubstituierte ftinf Hydrid-Aquivalente. Die gegeniiber den komplexen Metallhydriden mehr verbrauchten Hydrid-Aquivalente werden vom Amin-Stickstoff-Atom als Amin-Boran (R3N BH3, s. S. 7ff.) gebunden. Man fiihrt die Reaktion in siedendem THF oder in Bis-[2-methoxy-athyl]-ather durch. Mono- und disubstituierte Carbonsaure-amide werden in einer Stunde, unsubstituierte aliphatische in zwei, aromatische in acht Stunden reduziert1. 

---