Borazine Analogues

The cyclo trimer (CgHn)P-B(mes) 3 has been prepared and shown to be based on a planar ring of C, B and pyramidal P atoms. 

This boraphosphene compound is the phosphorus analogue of borazine (NH-BH)3 (9.60a) and, like the latter, is probably based on a delocalised p bonding system which can be at least partially represented as (9.60b) [24]. Equal ring distances and a planar ring have been found in (9.60c) [25]. 

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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... 

Fused Rings and Polymers. Borazine analogues of naphthalene and substituted phenalenes are known the latter compound is formed by reaction of distannylamine and a large excess of tris(methylthio)borane (137). A general method for the preparation of the polycyclic borazines using fused carbon—heteroatom rings, where X = O, NR and n = 2,3, has been given (137). 

Normally the trimeric borazines, analogues of benzenes, are produced. Some methods of preparing alkylborazines are indicated. The borazine ring is retained on nucleophilic replacement of chlorine in chloroborazines by a variety of other groups. 

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 ... 

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). 

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. ... 

The behavior of B-triamino-N-tris(trimethylsilyl)borazine was in good agreement with the ring opening mechanism. This compound was much more reactive than its phenyl analogues thus, the pure monomer could not be Isolated. The product obtained from the... 

Analogues of borazine are shown in Scheme 63 the planarity of 148 indicates some aromatic character. Some compounds with P and As were found to prefer... 

Scheme 63. Analogues of Borazine with Elements from the Same Groups of the Periodic System Representation Suggested in Ref 190b...

Its structure features a planar AI3N3 an ay with uniform Al—N bond lengths of 1.782(4) A. It is an Al—N analogue of the well-known borazines and may be written in the alumazene form... 

Renewed interest in borazine derivatives has resulted from their possible application as precursors to boron nitride ceramics. For example, the inorganic analogue of styrene, (H->C=CH)B3NjH5i has been polymerized and decomposed to produce BN.72... 

Borazines phenanthrene. Inorganic chemistry has two (at least) analogues of benzene borazincs. 

Borazine is isoelectronic with benzene, as B=N is with C=C, (Fig. 16.21). in physical properties, borazine is indeed a close analogue of benzene. The similarity of the physical properties of the alkyl-substituted derivatives of benzene and borazine is ever more remarkable. For example, the ratio of the absolute boiling points of the substituted borazines to those of similarly substituted benzene is constant. This similarity in physical properties led to a labeling of borazine as "inorganic benzene." This is a misnomer because tbe chemical properties of borazine and benzene are quite different Both compounds have aromatic rr clouds of electron density with potential for delocalization over all of the ring atoms. Due to the difference m electronegativity between boron and nitrogen, the cloud in borazine is "lumpy" because more electron... 

A boron-phosphorus analogue of borazine has been synthesized rather recently.73... 

Hydrogenation of borazine yields cyclic nonplanar B3N3H12, a cyclohexane analogue. Indeed, many if not most small hydrocarbons have their B-N counterparts, e.g.,... 

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