Site-selective functionalization of Si₆R₆ siliconoids

The recent progress in the synthesis of partially substituted neutral silicon clusters (siliconoids) revealed unique structures and electronic anisotropies that are reminiscent of bulk and nano surfaces of silicon. Here, we report the selective 2-lithiation of the global minimum Si₆R₆ siliconoid at a different vertex than in the previously reported isomeric 4-lithiated derivative (R = 2,4,6- Pr₃C₆H₂). In order to enable an intuitive distinction of the vertices of the global minimum Si₆R₆ scaffold (which can be considered the silicon analogue of benzene in terms of thermodynamic stability), we introduce a novel nomenclature in analogy to the ortho-meta-para nomenclature of disubstituted benzenes. By treatment of the 2-lithiated Si₆ cluster with Me₃SiCl, SiCl₄ H₃B·SMe₂, (Me₂N)₂PCl as well as with carboxylic acid chlorides RCOCl (R = Bu, Ph) various 2-functionalized Si₆ clusters were obtained and characterized in solution and - in most cases - the solid state. The structural and spectroscopic effect of the position of the newly introduced functional group is discussed by comparison to the corresponding 4-functionalized derivatives.