Toralf Peymann

Aromatic Polyhedral Hydroxyborates: Bridging Boron Oxides and Boron Hydrides

No explosion, but per-B-hydroxylation occurs if the icosahedral boron hydrides [closo-B12 H12 ](2-) (see picture), [closo-CB11 H12 ](-) , or closo-1,12-(CH2 OH)2 -1,12-C2 B10 H10 are refluxed in 30 % hydrogen peroxide. Thus, the three isoelectronic species [closo-B12 (OH)12 ](2-) , [closo-1-H-1-CB11 (OH)11 ](-) , and closo-1,12-H2 -1,12-C2 B10 (OH)10 were obtained. ○=BH, ○=BOH.

Aromatische polyedrische Hydroxyborate: eine Brücke zwischen Boroxiden und Borhydriden

Keine Explosion, sondern per-Borhydroxylierung tritt ein, wenn die ikosaedrischen Borhydride [closo-B12H12]2−, [closo-CB11H12]− oder closo-1,12-(CH2OH)2-1,12-C2B10H10 in 30proz. Wasserstoffperoxid unter Ruckflus erhitzt werden. Bei diesen Umsetzungen entstanden die drei isoelektronischen Verbindungen [closo-B12(OH)12]2− (Reaktion gezeigt), [closo-1-H-1-CB11(OH)11]− bzw. closo-1,12-H2-1,12-C2B10(OH)10. ○ = BH, ○ = BOH.

An unpaired electron incarcerated within an icosahedral borane cage: synthesis and crystal structure of the blue, air-stable {[closo-B12(CH3)12]·}– radical

Oxidation of the permethylated icosahedral borane [closo-B12(CH3)12]2– 1, by ceric(IV) ammonium nitrate in acetonitrile affords the blue, air-stable paramagnetic anion {[closo-B12(CH3)12]·}– 2, which has been characterized, among other means, by X-ray crystallography.

Recent Developments in the Chemistry of [B12H12]2-

The dodecaborate(2-) cluster [B12H12]2-, 1, is less frequently found as the boron component in drugs designed for BNCT than the isoelectronic carboranes C2B10H12. The carboranes contain C—H vertices that are easily modified by employing methods of organic chemistry.1 Thus, it is facile to link these carborane clusters to tumor-targeting moieties. Furthermore, the B—H vertices of the carboranes differ in reactivity depending on their position relative to the electron-withdrawing carbon atoms. This difference allows for the selective modification of certain B—H vertices. The anion 1, on the other hand, consists of 12 identical boron atoms. Therefore, it is difficult to control the degree of substitution and the regiospecifity of reactions performed on the icosahedral framework of 1. For example, the diiodination of 0-carborane gives exclusively the 9,12-isomer, whereas it leads to an isomeric mixture for 1.2 Relative to the carboranes, however, the dodecaborate(2-) cluster offers advantages such as its stability regarding basic degradation, water-solubility of its derivatives, and higher boron content.