Boron-nitrogen rings

The ring compound MeAlNDipp 366a 73a (Fig. 11) is an analog of bora-zine, (HBNH)3 and its derivatives, which are in turn isoelectronic and isostructural with benzene. While this family of boron-nitrogen rings is... 

Turner, H. S., and R. J. Warne A New Boron-Nitrogen Ring System. The Tetrameric Borazynes, Boron-Nitrogen Chemistry. Advances in Chemistry, Series 42. Amer. Chem. Soc. p. 290 (1964). 

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. 

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. 

The procedure described represents the conversion, through a change in the coordination number of boron and nitrogen, of a six-membered boron nitrogen ring to a four-membered boron nitrogen ring.1 The absence of other reaction products in the direct union simplifies the purification problem. 

Preparative Aspects of Boron-Nitrogen Ring Compounds... 

Several recent reviews have discussed the chemistry of boron-nitrogen compounds with particular emphasis on boron-nitrogen ring systems x 7>. 

One of the major problems in the chemistry of three-coordinated boron-nitrogen compounds is their relative instability towards hydrolysis 79>8°). This feature reduces their possible applications in many areas such as in the medicinal field or utilization for polycondensation-products. However, steric hindrance by bulky substituents on the borazine ring leads to compounds with enhanced hydrolytic stability, particularly when no solvent is present in which they may dissolve. This observation has resulted in extensive research on sterically hindered boron-nitrogen ring compounds. 

While the mercury compound shows localized N—Hg bonds, the TADB-system (which is isoelectronic with cyclopentadiene) forms a low-spin complex with iron. This was the first identified example of a sandwich-compounds of a boron-nitrogen ring. The complex is prepared by adding an etheric solution of TADBLi to a suspension of FeCl2 in tetra-hydrofuran. 

The infrared spectrum of the compound shows the boron-nitrogen ring frequency at 1392 cm.-"1. Its XH n.m.r. spectrum shows a sharp singlet at —3.1 p.p.m. (TMS standard). 

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