The Synthesis and Structural Characterization of Polycyclic Derivatives of Cobalt Bis(dicarbollide)(1^–)

The cobalt bis­(dicarbollide) anion [(1,2-C₂B₉H₁₁)₂-3,3′-Co]⁻ (1^–) is an increasingly important building block for the design of new biologically active compounds. Here we report the reactions of lithiated 1^– with N-(ω-bromoalkyl)­phthalimides Br-(CH₂)_n-N­(CO)₂NC₆H₄ (where n = 1 to 3) that give a number of new compounds substituted at dicarbollide carbon atom positions. For n = 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-a]­isoindol-5­(9bH)-1,2,3-dihydro-9b-yl)-(1-cobalt­(III) bis­(1,2-dicarbollide)­(1^–) (2^–) and 1-(2H-[1,3]-oxazino­[2,3-a]­isoindol-6­(10bH)-1,3,4-dihydro-10b-yl)-(1-cobalt­(III) bis­(1,2-dicarbollide)­(1^–) (4^–) ions with isoindolone functions containing either five- or six-membered lateral oxazine rings. Additionally, products (tetrahydro-2-benzo­[4,5]­furan-1­(3H)-1-[3,3]-yl-)-1,1′-μ-cobalt­(III) bis­(1,2-dicarbollide)­(1^–) (3^–) and (2-(azetidin-yl-carbonyl)­benzoyl-)-1-cobalt­(III) bis­(1,2-dicarbollide)­(1^–) (5^–) 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 n = 1, only the anticipated methylene amine derivative [(1-NH₂CH₂-1,2-C₂B₉H₁₁)­(1′,2′-C₂B₉H₁₁)₂-3,3′-Co]⁻ (6^–) was isolated in low yield after cleavage of the phthalimide intermediate species. The molecular structures of all isolated cyclic products 2^– to 5^– were confirmed by single-crystal X-ray diffraction studies, and the structure of cobalt bis­(dicarbollide)-1-CH₂NH₂ 6^– 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.