Borazines structure

Generally, during hydroboration polymerization of dicyano compounds, the formation of the borazine structures that have a six-membered boron-nitrogen ring (scheme 19a) and dihydroborated end groups (scheme 19b) as a structural defect is unavoidable. The borazine cross-linked structures often cause the gelation, and dehydroboration causes a decrease in molecular weight. 

Compounds belonging to the borazine structural class which is based on a six-membered ring of alternating boron and nitrogen atoms are readily prepared by a number of reactions including... 

Today, there exist a wide variety of boron-containing polymers including ring systems such as borazines (structure 11.41), boroxines (structure 11.42), and triphosphatoborins (structure 11.43),... 

To improve the thermal durability and inflammability of the materials, we have been investigating organoboron structures to hybridize with silicon polymers. In this field, the preceramic character of the borazine structure [2] and its catalytic function for anti-oxidation [3] are already known. Lately Chujo reported hydroboration polymerization to obtain boron-based polymers [4]. 

FIGURE 16.6 Cyclic pentamer, [H2NBH2]5 (a) and linked borazine structure (b). 

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. 

C21-0046. Borazine (B3 N3 Hg ) is a planar molecule analogous to benzene (Cg Hg ). Write the Lewis structure and describe the bonding of borazine. 

Figure 46 The planar structures of the boron ring systems, borazine (71) and boroxine (72), with nonexistent aromaticities and of triphosphatriborin (73) with an appreciable degree of aromaticity. (Adapted from ref. 95.)...

Clearly, branching chains containing other borazine units on the free aminoboryl site cannot be excluded, even though such chains are difficult to obtain because of steric hindrance. Nevertheless, a structure that is consistent with the characterization data is proposed in scheme 8. 

By analogy with B-trialkylaminoborazi ne and polyborazine derived therefrom, the first route envisioned to poly(borylaminoborazine) was the thermal condensation of molecular precursors under a convenient atmosphere. As detailed earlier the innovative idea behind this procedure is to tailor the polymeric precursor structure by increasing the distance between the two borazinic rings. For that purpose, we explored... 

In this section, syntheses of a variety of inorganic nitrogen compounds are described. The syntheses include those of triazanium chlorides alkylamino derivatives of boron, arsenic, and tin and trimeric and tetrameric boron-nitrogen ring structures as exemplified by borazine (HNBH)3. 

Boron also forms many other compounds with nitrogen. One of the most interesting of these is bora-zine, B3N3HS (m.p. -58 °C, b.p. 54.5 °C). Shown here is the structure ofborazine, which is similar to the structure of benzene. In fact, borazine has sometimes been referred to as "inorganic benzene."... 

When subjected to high temperature under vacuum, borazine loses hydrogen and polymerizes to yield products known as biborazonyl and naphthazine, whose structures are similar to biphenyl and naphthalene, respectively. 

On a larger scale, the reaction of (NH2)2CO with B(OH)3 at high temperature in an atmosphere of ammonia is used to produce borazine. Trichloroborazine, B3N3CI3H3, has the structure... 

Borazine, 21, is sometimes called inorganic benzene. Like benzene, it achieves a high-symmetry D6h equilibrium structure with equivalent NRT bond orders (1.380)... 

Tris(diphenylmethyleneamino)borane was obtained according to Eq. (30). Exchange reactions of monomeric and dimeric iminochloroboranes with various fluorides could not be effected. However, this lack of reaction is to be expected, since it is well known from borazine chemistry that substitutions which would require a structural change in order to obtain a stable product will not occur 20>. (Diphenylketimino)trimethylsilane (rather than diphenylketimine lithium) has been utilized successfully to prepare (diphenylmethyleneamino) dihaloboranes. This type of reaction is in accordance with earlier observa-... 

A theoretical study on the structures, magnetical properties, and energetics of phosphorus analogues of borazine, E2G3H6 191 (E = B, Al, Ga G = N, P, As), compared to those of other borazine analogues, E3J3H3 192 (J = O, S, Se) and to phosphazene (194),234 shows that results could vary with function of the reference system. Some compounds with P and As heteroatoms were found to prefer nonplanar geometries (Scheme 74). Contradictory results were... 

There are similar analogues to other aliphatic hydrocarbons, for example H2N - BH2, which is isoelectronic with ethene, and a most interesting compound called borazine, B3N3H6, which possesses physical properties remarkably like those of the aromatic analogue benzene, C6H6. Borazine has, in fact, a ring structure like benzene ... 

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