The Synthesis and Structural Characterization of Polycyclic Derivatives of Cobalt Bis(dicarbollide)(1(-))
Abstract
The cobalt bis(dicarbollide) anion [(1,2-C2B9H11)2-3,3'-Co]- (1-) is an 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. 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 and NMR spectroscopy. The synthetic method described presents a facile route to new cobalt bis(dicarbollide) derivatives substituted by polycyclic structural motifs with potential biological activity.