| Some aspects of chemistry of the previously known inner methyl sulfonium salts of closo-[B12H12]2− , [Me2SB12H11]−, 1,7- and 1,12-(Me2S)2B12H10, and 1,2-(Me2S)2B12H10, which was isolated and characterized for the first time, have been studied. Reactions with nucleophiles such as phthalimide and thiolate lead to formation of methyl thioethers [MeSB 12H11]2− and [(MeS)(Me2S)B 12H10]−. Excess nucleophile produces methyl dithioethers [(MeS)2B12H10] 2−. Alternatively, [MeSB12H11] 2− and [(MeS)2B12H10] 2− can be obtained by reduction of the corresponding sulfonium salts by sodium or potassium in liquid ammonia. Various derivatives of these thiols have been synthesized through the alkylation and acylation reactions including (Bn2S)2B12H10, 1,7-( i-Pr2S)2B12H10 and [C 6H5C(O)SB12H11]2−. Methyl thioethers have been alkylated by a variety of alkyl halides and tosylates. By this method such functional groups as phosphonate and gem-bisphosphonate can be coupled to the B12-moiety. Propargylation followed by a reaction with B10H12(CH3CN)2 leads to the ortho-carborane-dodecaborane oligomers containing two or three icosahedral cages linked by S(CH3)-CH2 units.; Similar to meta-carborane, electrophilic substitution in 1,7-(Me2S)2B12H10 occurs at positions 9 and 10. Its chloro-, bromo-, iodo-, arylthio- and phenylselenoderivatives have been prepared as well as the bromo- and iododerivatives of the 1,12-isomer. Contrary to the behavior of ortho-carborane, 1,2-(Me 2S)2B12H10 did not produce a single product upon bromination or iodination. The iododerivatives of 1,7- and 1,12-(Me 2S)2B12H10 enter the palladium-catalyzed boron-carbon cross-coupling reactions with Grignard reagents providing B-alkyl- and arylsubstituted derivatives not easily available by any other methods.; All new compounds have been characterized by multinuclear NMR and either mass-spectrometry or elemental analysis. For some the molecular structures have been obtained by X-ray single-crystal diffraction. Several experimental facts have led to the conclusion that in methyl thioethers and thiols the electron density is donated from the cage to a sulfur atom resulting in a partial double-bond character for a B-S bond. (Abstract shortened by UMI.)... |
