Synthesis and characterization of sulfide, sulfide-sulfonium, and bissulfide derivatives of [B12H12]2-. Additivity of Me2S and MeS- substituent effects in 11B NMR spectra of disubstituted icosahedral boron clusters

The 1,2-, 1,7-, and 1,12-isomers of (Me2S)2B12H10 (O, M, and P) react with potassium phthalimide in DMF or EtSNa in CH3CN/EtOH upon reflux producing the corresponding isomers of [(MeS)(Me2S)B12H10]- (O1-, M1-, P1-). If excess of either nucleophile is used, [Me2SB12H11]- (1) and O, M, P can be converted into dianions [MeSB12H11]2- (2) and [(MeS)2B12H10]2- (O2-, M2-, P2-). The use of EtSNa is recommended since it facilitates the isolation of products compared to the potassium phthalimide method. When 1 or O, M, P are treated with an excess of an alkali metal (Na, K) in liquid ammonia at -40 degrees C, sulfide 2 or bissulfide dianions O2-, M2-, P2- are obtained cleanly and almost instantly. While both the nucleophilic substitution and alkali metal reduction methods are useful for the synthesis of dianions 2, O2-, M2-, and P2-, only the former method is suitable for the synthesis of the sulfide-sulfonium anions O1-, M1-, P1-. The analysis of the 11B NMR spectra of 1, O, M, P and anions derived from them demonstrated that the spectra of the disubstituted species can be predicted qualitatively, keeping in mind the simple substituent effects obtained from the spectra of monosubstituted anions 1 and 2. Some evidence is found for small partial double bond character of the B-SMe bonds in anions. [MePPh3]+ salts of [MeSB12H11]2- (2) and [1-(MeS)-7-(Me2S)B12H10]- (M1-) are structurally characterized by single-crystal X-ray diffraction analysis. Crystal data: [MePPh3]2[MeSB12H11], P2(1) (No. 4), a = 9.243(1) A, b = 18.272(1) A, c = 12.548(1) A, beta = 103.17(1) degrees, Z = 2; [MePPh3][1-(MeS)-7-(Me2S)B12H10], P1 (No. 2), a = 9.278(2) A, b = 12.003(5) A, c = 14.819(7) A, alpha = 112.18(4) degrees, beta = 105.61(3) degrees, gamma = 92.91(3) degrees, Z = 2.