Synthesis of nido-Carborane Derivatives with a Pendant Dimethylammonium Group

An efficient method was developed for the introduction of a dimethylammonium group into the pendant substituent at nido-carborane based on the alkylation of the trimethylammonium salt of 1-mercapto-ortho-carborane with α,ω-dihaloalkanes and subsequent reaction of the obtained ω-haloalkyl derivatives with dimethylamine. Thus, the reaction of (Me3NH)[1-S-1,2-C2B10H11] with an excess of 1,2-dibromoethane and 1,3-dibromopropane afforded the corresponding ortho-carborane derivatives 1-Br(CH2)nS-1,2-C2B10H11 (n = 2, 3). Reactions of these derivatives with an excess of dimethylamine in tetrahydrofuran resulted in the exchange of the halogen atom for a dimethylamino group and were accompanied by deboronation of the closo-carborane cage to the anionic nido-form. As a result, two C-substituted nido-carborane derivatives with a pendant Me2NH-group and varying spacer lengths between the carborane cage and the donor fragment, 7-Me2HN(CH2)nS-7,8-C2B9H11 (n = 2, 3), were synthesized. The obtained compounds are of interest as heterofunctional ligands of the η5κ1-type.