B-aminoborazine

B-Aminoborazines are of particular interest for fundamental studies. In these compounds, boron is bonded to three nitrogen atoms with two different types of environment. B-Aminoborazines are also useful precursors for the synthesis of thermally stable polymers. Quite a few polycondensates of aminoborazines and copolymerisates with organic difunctional molecules have been described 4>. Of major interest are difunctional borazines yielding linear polycondensates. The condensation of l,3,5-tris(2,6-dimethylphenyl)-2,4-dichloroborazine (cf. Section II.2.5) with aliphatic, aromatic, and heterocyclic diamines, as well as the preparation of the same linear polyborazines by transamination of 1,3,5-tris(2,6-dimethylphenyl)2,4-bis(diethyl-amino)borazine with diamines was studied 139). 

The reactions of [NP(NMe2)2]a[NPX(NMe2) ]b(NPX2) (X=C1, NH2) with B3N3Me3NH2 or B3N3Me3Cl3 followed by NHj have been utilized to generate poly(phosphazenes) with B-aminoborazine substituents. Pyrolysis of these polymers gave over 50% ceramic yield... 

In a two-step synthesis procedure, the B-trichloroborazine reacts with ammonia or amine derivatives as linking reagents to form B-aminoborazines which are subsequently thermolyzed at moderate temperatures to generate poly[B-aminoborazine] [25 7]. Pioneering works in this chemistry have described the preparation of B-aminoborazine-type polymers through a two-step procedure [31,32,34], but no attention has been given to the materials as BN precursors. 

In the 1970s, Tanigushi et al. reported the preparation of boron nitride fibers from a melt-spinnable poly[B-aminoborazine] (Eq. 14.4) [25], However, Uttle information has been provided and the lack of reproducibihty in the melt-spinning process rendered the production of BN fibers difficult. 

Unsymmetrically substituted aminoborazines resulted from the reaction of amines with B-alkylthioborazines 144>. The first optically active borazine has been obtained from the reaction of 2,4,6-trichloroborazine and (+)2-butylamine 145> using triethylamine as a hydrogen chloride acceptor. B-Monoaminoborazine, HaNsBaH NH ) and isotopically labeled derivatives thereof have been prepared by photochemical reaction from borazine and ammonia in a gas phasereaction 14fi-147>. 

The structure of this compound has been confirmed by X-ray analysis 172>. The first s-diazadiborines were obtained by pyrolysis of tris(t-butyl-amino)borane 166 167). Other less hindered tris(amino) boranes form aminoborazines or poly(aminoborazines) the nature of the product depends on pyrolysis time and utilized temperature 175>. Exocyclic B—N bonding appears to contribute to the stability of 1,3-diamino-diazaborines thereby explaining their chemical stability as compared to that of the corresponding tetraorganocompounds. 

A poly(aminoborazine), precursor for hexagonal boron nitride obtained by reaction of borazine B3N3H6 with ammonia, and its pyrolysis derivatives have been extensively characterised by and B MAS NMR. ... 

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