Dimethylsulfide-dicarbaborane chemistry. Isolation and characterisation of isomers [9-(SMe2)-nido-7,8-C2B9H10-X-Me] (where X = 1, 2, 3 and 4) and some related compounds. An unusual skeletal rearrangement

Abstract

Oxidative coupling by FeCl₃ of the [nido-7,8-C₂B₉H₁₁-9-Me]⁻ anion 1a with SMe₂ yields a mixture of four isomers of 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-X-Me, where X = 1, 2, 3 and 4 (compounds 2a, 2b, 2c and 2d respectively). On high dilution of the reaction mixture, the 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-10-Me 2e isomer is also isolated in a low yield. The isomers are separated by HPLC, and are identified and characterised by NMR spectroscopy and by single-crystal X-ray diffraction analyses of 2c and 2d. The formation of the products implies an unexpected cluster rearrangement, which is discussed in terms of dsd and vertex-flip reaction pathways. Two additional isomers, 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-5-Me 2f and 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-6-Me 2g occur when [nido-7,8-C₂B₉H₁₁-5-Me]⁻1b is used as the starting substrate, in a reaction in which no cluster rerarrangement is observed. The corresponding bromide, [nido-7,8-C₂B₉H₁₁-5-Br]⁻1c, behaves similarly, forming only 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-5-Br 2h and 9-(SMe₂)-nido-7,8-C₂B₉H₁₀-6-Br 2i.