Borazines

Borazine, B3N3H6, was first prepared by thermolysis of the diborane ammonia adduct [(BH2)(NH3)2] [BH4] . More convenient procedures for the laboratory preparation of this important ring system in multigram quantities involve either (a) the decomposition of ammonia- borane [eqn (9.1)] or (b) the reaction between ammonium sulfate and sodium borohydride [eqn (9.2)]. The latter method provides a convenient and economical synthesis of borazine. 

An alternative route to -substituted mono-, di- and trialkylborazines involves the RhH(CO)(PPh3)3-catalysed reactions of borazines with alkenes, as illustrated in eqn (9.4) for the trialkyl-substituted derivatives.  

The electronegativity difference between boron and nitrogen (2.0 and 3.0, respectively, on the Pauling scale) results in a polar B-N bond. The regio-selectivity of the reactions of borazines with electrophiles and nucleophiles can be understood in this context. Thus the reaction of borazine with three equivalents of HCl produces (C1HBNH2)3 in which the proton seeks out the nitrogen centres and the chloride ions become attached to boron.  

5 -Trialkylated borazines R3B3N3H3 are deprotonated by organolithium reagents, but other reaction pathways also occur.For example, the reaction of Me3B3N3H3 with one equivalent of methyllithium produces the solvated monolithium derivative [(Me3B3N3H2)Li(OEt2)]2 (9.9), which is dimeric in the solid state. The formation of di- or trilithiated derivatives. 

Synthetic methods are available for the incorporation of other p-block elements into a borazine ring. An illustration of the potentially versatile methodology using an NBNBN building block is given for the tellurium-containing borazine 9.11 in eqn (9.5).  

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There are similar analogues to other aliphatic hydrocarbons, for example HjN BHj, which is isoelectronic with ethene, and a most interesting compound called borazine, B3N3H6, which possesses physical properties remarkably like those of the aromatic analogue ... 

Borax stability Boraz anaphthalene Borazine [6569-51-3] Boraz ines Borazon... 

The emphasis in the approaches to boron nitride [10043-11 -5] BN, precursors has been concentrated on cycHc compounds. There have been recent reports of trimethylsilyl-substituted aminoboranes being evaluated as B—N precursors. These are linear borylamines containing up to four boron atoms. Compounds were also synthesized with free —NH2 groups amenable to condensation with either dihaloboranes or dihaloborazines (65) and offering suitable monomers for linear B—N polymer synthesis and borazine-ring-linking appHcations. 

This works well for all nido- and arachno-boranes but not for the c/o o-dianions, which are much less reactive. Reactions of B2H6 with NH3 are complex and, depending on the conditions, yield aminodiborane, H2B(/r-H)(/r-NH2)BH2, or the diammoniate of diborane, [BH2(NH3)2]-[BH4] (p. 165) at higher temperatures the benzene analogue borazine, (HNBH)3, results (see p. 210). 

The cyclic borazine (-BH-NH-)3 and its derivatives form one of the largest classes of B-N compounds. The parent compound, also known as inorganic benzene , was first isolated as a colourless liquid from the mixture of products obtained by reacting B2H6 and NH3 (A. Stock and E. Pohland, 1926) ... 

Numerous other reactions have been documented, most of which are initiated by nucleophilic attack on B. There is no evidence that electrophilic substitution of the borazine ring occurs and conditions required for such reactions in benzenoid systems disrupt the borazine ring by oxidation or solvolysis. However, it is known that the less-reactive hexamethyl derivative B3N3Mee (which can be heated to 460° for 3 h without significant decomposition)... 

IV-substituted and B-substituted borazines are readily prepared by suitable choice of amine and borane starting materials or by subsequent reaction of other borazines with Grignard reagents, etc. Thermolysis of monocyclic borazines leads to polymeric materials and to polyborazine analogues of naphthalene, biphenyl, etc. ... 

Borazine, (HBNH)3, analogous to benzene prepared by A. Stock and E. Pohland. 

The aromaticity of such inorganic ring systems as borazine, the phosphonitrilic halides (69), and the thiazyl halides (70) has been studied extensively from a theoretical viewpoint. ... 

B-C bonds, 3, 97 B-N bonds, 3, 97 B-O bonds, 3,94 B-P bonds, 3, 97 B-Si bonds, 3, 97 oxo acid anion complexes, 3, 96 Borates, alkoxo-, 3, 94 Borates, amidotrihydro-, 3,92 Borates, aryloxo-, 3, 94 Borates, carboxylato-, 3,96 Borates, catechol, 3,95 Borates, chlorosulfato-, 3,97 Borates, dicarboxylato-, 3,96 Borates, dipyrazol-l-yl-, 3, 92 Borates, halogeno-, 3,92 Borates, halogenohydro-, 3,90 Borates, hydro-, 3,90 Borates, hydrohydroxo-, 3,90 Borates, hydropyrazol-l-yl-, 3, 92 Borates, hydroxo-, 3,94 Borates, hydroxycarboxylato-, 3,96 Borates, inositol, 3, 95 Borates, monoalkyl-, 3, 92 Borates, monophosphido-, 3, 92 Borates, peroxohydroxo-, 3, 94 Borates, polyol, 3, 95 Borates, pyrrol-l-yl-, 3, 92 Borates, sulfato-, 3, 97 Borates, tetrabromo-, 3, 92 Borates, tetrachloro-, 3, 92 Borates, tetrafluoro-, 3, 92 minerals, 6, 847 Borates, tetrahalogeno-mixed, 3, 93 nB NMR, 3, 92 Borates, tetraiodo-, 3, 92 Borates, tetranitrato-, 3, 96 Borates, tetraperchlorato-, 3, 97 Borates, tripyrazol-l-yl-, 3, 92 Borax, 3,101 Borazines... 

Borazine, B3N3Hft, a compound that has been called inorganic benzene because of its similar hexagonal structure (but with alternating B and N atoms in place of C atoms), is the basis of a large class of boron—nitrogen compounds. Write its Lewis structure and predict the composition of the hybrid orbitals used by each B and N atom. 

Another useful deposition reaction is the decomposition of borazine. This is a condensation reaction which produces an amorphous BN with residual hydrogen incorporation ]... 

One of the first reports related to the preparation of macrocyclic ring systems with boron atoms deals with the transformation of m-difunctionalized borazines into cyclic di-, tetra-, or hexaborazines [16-19]. 

The cyclic dimeric borazine derivatives 2 and 3 can be prepared by reaction of 2,4-dichloro-l,3,5,6-tetramethylborazine with aromatic 1,3-dihydroxy and l-amino-3-hydroxy compounds (Fig. 2). The products are obtained in yields... 

By reaction of 2-alkyl-4,6-dichloro-l,3,5-trimethylborazines (alkyl = methyl, ethyl, i-propyl) with bis(trimethylsilyl)amine the tetrameric borazine ring systems 4-6 are produced (Fig. 2) they can be purified by several successive vacuum sublimations (yields 4-60%). If the borazines carry n-propyl and tert-butyl groups in the 2-position or if methylbis(trimethylsilyl)amine is used to bridge the borazine molecules, the macrocyclic ring formation is inhibited [17, 18]. 

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