1,1-substituted ferrocenes. Although we were able to isolate the persilylated derivative [FeC10DMS10] (6) the demonstrated synthetic approach is inconvenient for further synthetic applications in terms of selectivity and experimental effort. In order to generate highly overcrowded metallocenes in a selective manner we modified the substitutional pattern to 1,1'-disubstituted ferrocenes. Here the presence of methyl groups should in part compensate the electron-withdrawing and steric effects of the silyl substituents. The polybrominated compound [FeC10Br8Me2] (7) was synthesized by eightfold mercuration of 1,1'-dimethylferrocene followed by bromination with KBr3, in analogy to the synthetic protocol to decabromoferrocene. The silylation of the corresponding metallocene was carried out with elemental magnesium and DMSCl in anhydrous THF. In contrast to the analogous reaction of decabromoferrocene the perfunctionalized derivative was obtained selectively in high yields. Due to the high selectivity of the reaction step the purification of the substrates is accomplished easily by recrystallization instead of complex chromatographical methods. The obtained compound [FeC10DMS8Me2] (8) was analyzed by NMR, UV/VIS and single-crystal XRD. The polysilylated metallocenes show similar features in as [FeC10DMS10] (6). In the 1 H and 13 C NMR spectra the signals which were assigned to the methyl groups attached to silicon split into a set of four signals indicating again a hindered rotation along the Si-C Cp axis. In the UV/VIS spectra the observed absorption maximum in the visible region at λmax = 490 nm is again red-shifted, indicating decreased HOMO-LUMO energy gaps. The observed wavelengths are similar to those of [FeC10DMS8H2] (4b: λmax = 495 nm) with tetrasilylated Cp ligands. Single crystals of compound 8 were obtained upon crystallization from MeOH/THF mixtures. The molecular structure shows again elongated metal-Cp bonds of 2.082(4) -2.099(4) Å compared to those of unsubstituted ferrocene (Fe-C: 2.051(2) -2.063(2) Å ). The Cp rings deviate from a parallel arrangement by only 4.6(2)° due to the lower steric demand of the methyl groups. The silyl groups are found out of the Cp plane (5.3 -20.9°) in spite of the reduced steric demand induced by the methyl groups.