R$\rm{^{{\ast}}_{4}}$Tl(3)Cl and R$\rm{^{{\ast}}_{6}}$Tl(6)Cl(2) (R*=SitBu(3))-The First Compounds with Larger Clusters Containing Covalently Linked Thallium Atoms Compounds of Silicon, Part 143. Supersilyl Compounds of Boron and Its Homologues, Part 12. This work was supported by the Deutsche Forschungsgemeinschaft and by the Fonds der Chemischen Industrie. Part 42: N. Wiberg, W. Niedermayer, J. Organomet. Chem. 2001, in press; Part 11. M. Kehrwald, W. Köstler, A. Rodig, G. Linti, T. Blank, N. Wiberg, Organometallics 2001, in press.