Boroxoles

Fig. 9. The borate glass stmctural groups where = boron Q — oxygen (a) boroxol (b) pentaborate (c) triborate and (d) diborate (142).

In THF gelost wird Kohlenmonoxid bei 20° durch Diboran und Natriumboranat als Katalysator zu Trime-thyl-boroxol reduziert (vgl. Bd. XIII). ... 

Diboran reduziert Monocarbonsauren in THF oder 1,2-Dimethoxy-athan, mit dem Losungsmittel als Boran koordiniert, in zwei Schritten. Zuerst wird bei -20° schnell und quantitativ Triacyloxy-boran gebildet, im zweiten langsameren Schritt (25°, 1 Stde.) Trialkoxy-boroxol, das nach Hydrolyse den gewiinschten Alkohol liefert4. 

Phenyl-l,3,2-benzodioxaborole has B—O bond lengths of 1.394 A, appreciably longer than in boroxoles and boric acid (74AX(B)1876>. 

Trimethylborate is a colourless transparent liquid which boils at 68.7°C. It is used as gaseous welding flux and as a parent component for some boron derivatives, such as sodium and potassium boranes, trimethoxy-boroxol, etc. E.g., trimethoxyboroxol can be rather easily formed when trimethylborate interacts with boron anhydride. 

Figure 7 Structural representation of boron oxide (B2O3) glass. The giant 2-D skeleton is formed by BO3 triangles sharing comers. Specific B3O3O3/2 boroxol groups can be present in the structure...

Fig. 5.30. Two boroxol (BjOJ rings linked by a shared oxygen atom (filled circles, boron atoms open circles, oxygen atoms).

The boroxol ring, and its protonated form, HjBjO, have also... 

Tossell, J. A., and P. Lazzeretti (1990). Calculation of the structure, vibrational spectra, and polarizability of boroxine, H3B3O3, a model for boroxol rings in vitreous BjO,. J. Phys. Chem. 94, 1723-24. 

Reactions of this type are somewhat less satisfactory for preparation of mixed diboron derivatives containing boron-carbon bonds. Thus, while tetrakis(dimethylamino)diborane(4) is readily hydrolyzed to tetrahydroxy-diborane(4) in aqueous acid, l,2-bis(dimethylamino)-l,2-diethylborane(4) reacts with formation of hydrogen and cleavage of the boron-boron bond 14). Reaction of the dibutyl analog with a twofold excess of water gave the dimethylamine adduct of the boroxole... 

Table III. Infrared Vibrations of Boroxole Ring Structure Goubeau h- ...

Figure 7.13. One-dimensional B NMR spectra of B2O3 glass acquired using several different techniques for narrowing the spectra and improving resolution. Asterisks denote spinning sidebands. Peaks marked A and B arise from the boroxol ring site and the non-ring BO3 site respectively. Adapted from Youngman et al. (1996).

The names borazole, boroxole and borthiole, respectively, for the three compounds in Examples 4, 5 and 6 have been abandoned long ago as they imply five-membered rings in the Hantzsch-Widman system. The names borazin(e), boroxin and borthiin indicate six-membered rings with unsaturation and only one boron atom and one other heteroatom (although the order of the element name stems is wrong) and are also not acceptable. 

B03]3- in boroxol rings [BO3F] - and [B02F2p distorted tetrahedrons -O- bridges... 

Several authors prefer the name boroxyl to boroxol. In this book, boroxol is used as the nomenclature. 

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