The Synthesis and Structural Characterization of Polycyclic Derivatives of Cobalt Bis(dicarbollide)(1<sup>–</sup>)

The cobalt bis­(dicarbollide) anion [(1,2-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>)<sub>2</sub>-3,3′-Co]<sup>−</sup> (<b>1</b><sup><b>–</b></sup>) is an increasingly important building block for the design of new biologically active compounds. Here we report the reactions of lithiated <b>1</b><sup><b>–</b></sup> with <i>N</i>-(ω-bromoalkyl)­phthalimides Br-(CH<sub>2</sub>)<sub><i>n</i></sub>-N­(CO)<sub>2</sub>NC<sub>6</sub>H<sub>4</sub> (where <i>n</i> = 1 to 3) that give a number of new compounds substituted at dicarbollide carbon atom positions. For <i>n</i> = 2 and 3, substitution of the cobalt bis­(dicarbollide) anion is accompanied by cyclocondensation of the organic moieties to give polycyclic ring structures attached to the cage. Predominant products correspond to oxazolo­[2,3-<i>a</i>]­isoindol-5­(9b<i>H</i>)-1,2,3-dihydro-9<i>b-</i>yl)-(1-cobalt­(III) bis­(1,2-dicarbollide)­(1<sup>–</sup>) (<b>2</b><sup><b>–</b></sup>) and 1-(2<i>H</i>-[1,3]-oxazino­[2,3-<i>a</i>]­isoindol-6­(10b<i>H</i>)-1,3,4-dihydro-10<i>b</i>-yl)-(1-cobalt­(III) bis­(1,2-dicarbollide)­(1<sup>–</sup>) (<b>4</b><sup><b>–</b></sup>) ions with isoindolone functions containing either five- or six-membered lateral oxazine rings. Additionally, products (tetrahydro-2-benzo­[4,5]­furan-1­(3<i>H</i>)-1-[3,3]-yl-)-1,1′-μ-cobalt­(III) bis­(1,2-dicarbollide)­(1<sup>–</sup>) (<b>3</b><sup><b>–</b></sup>) and (2-(azetidin-yl-carbonyl)­benzoyl-)-1-cobalt­(III) bis­(1,2-dicarbollide)­(1<sup>–</sup>) (<b>5</b><sup><b>–</b></sup>) were isolated, which display unusual cyclic structures featuring a bicyclic benzofuranone ring attached in a bridging manner by a quarternary carbon to two skeletal carbon atoms and a ketobenzoic acid amide substituent with a side azetidine ring. However, in the case of <i>n</i> = 1, only the anticipated methylene amine derivative [(1-NH<sub>2</sub>CH<sub>2</sub>-1,2-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>)­(1′,2′-C<sub>2</sub>B<sub>9</sub>H<sub>11</sub>)<sub>2</sub>-3,3′-Co]<sup>−</sup> (<b>6</b><sup><b>–</b></sup>) was isolated in low yield after cleavage of the phthalimide intermediate species. The molecular structures of all isolated cyclic products <b>2</b><sup><b>–</b></sup> to <b>5</b><sup><b>–</b></sup> were confirmed by single-crystal X-ray diffraction studies, and the structure of cobalt bis­(dicarbollide)-1-CH<sub>2</sub>NH<sub>2</sub> <b>6</b><sup><b>–</b></sup> was delineated using density functional theory applied at BP86/AE1 level in combination with NMR spectroscopy. Thus, the synthetic method described herein presents a facile route to new cobalt bis­(dicarbollide) derivatives substituted by polycyclic structural motifs with potential biological activity.