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