The intermediate dicarba-nido-boranes
| Autor: | S. Heřmánek, J. Plešek |
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| Rok vydání: | 1974 |
| Předmět: | |
| Zdroj: | Pure and Applied Chemistry. 39:431-454 |
| ISSN: | 1365-3075 0033-4545 |
| DOI: | 10.1351/pac197439040431 |
| Popis: | The formation of several nido-carboranes, their structures, chemistry, some comparisons with nido-boranes and general stability rules are briefly reviewed. Oxidation of the 7,8-C2B9H2 anion was found to afford selectively various new nido-carboranes, namely, 5,6-C2B8H,2, n-C4B,8H22, iso-C4B18H22 and the C4B15H3 anion. The 5,6-C2B8H,2 was used as the starting material in syntheses of further new or known compounds, e.g. 1,2-C2B8H,0, 1,10C2B8H,O, 6,9-C2B8H,4, 5-Cl-6,9-C2B3H,3, l,3-C2B7H13 etc. Analogous oxidations of substituted (Br, C6H5) C2B9H ions and the direct bromination and deuteration of the parent carborane in bridge-positions resulted in derivatives which made it possible to elucidate the ''B n.m.r. spectrum of 5,6-C2B8FI,2. The n-C4B,8H22 is a new carborane type, consisting of two C2B9H1, units, bonded by two three-centre exo-bonds. The structure was solved by combination of selected reactions [BH3-insertion, splitting with Lewis bases, reduction of the C4B, 8H salt] and elucidation of structures of the compounds formed. The accompanying iso-C4B, 5H22 is, according to its n.m.r. spectra, composed of the 5,6-C2B8H11 and o-carborane fragments attached by means of a B—B bond probably in position 8 of the former compound and 3 of the latter framework. The C4B,8H anion was revealed as a C2B9H, ,H-C2B9H,, system with a hydrogen bridge bound to B[9] of each unit. The reaction of the 7,8-C2B9H 12 anion with nitrous acid results in degradative insertion with the formation of novel l0-N-7,8-C2B8H,, and 8,9-NH 2-5,6C2B8H,, nido species. Under forced conditions, the p-carborane was degraded to a new 2,9C2B9H '2 anion, the acidification of which led to the relatively stable 2,9C2B9H,3 nido-carborane. On the basis of an intercomparison of various nido-carboranes with other members of this family and with nido-boranes, general stability rules for nidocarboranes are proposed. INTRODUCTION While the nido-boranes represent the oldest class, the analogous nidocarboranes are relatively the youngest and least investigated group of the borane family'. This article deals with the intermediate dicarba-nidoboranes of the C2B7 to C2B9 series. As the first representative of this dicarba-nido-borane group, 7,8-dicarbanido-undecaborane(13) was discovered by Wiesboeck and Hawthorne2. 431 J. PLEEK AND S. HEkMANEK This compound was obtained by alkaline degradation of 1,2-dicarba-closododecaborane(12) followed by acidification of the fairly stable nido-anion 7,8-C2 B9H 12• H OBH •CH Figure 1. Formation of 7,8-C2B9H13 from o-carborane2 Another important compound of this series, the nido-carborane 1,3C2B7H13 was observed by Hawthorne et al.3 as the main product in the oxidation of the 7,9-C2B9H ion. Figure 2. Oxidation of the 7,9-C2B9H anion to 1,3-C2B7H13 The 1,3-C2B7H13 carborane was used as the starting material in the synthesis of a further member, the 5,7-C2B8H12 carborane4. |
| Databáze: | OpenAIRE |
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