All reactions including Grignard formation were carried out with DMSCl or DMSOTf in tetrahydrofuran (THF) by variation of conditions in terms of temperature and reaction time (ESI, Table ). For all reactions mass spectrometry reveals that the Grignard formation is complete since no brominated species were observed. However, the silylation step seems to proceed very slowly at high degrees of silylation, as the formation of decasilylferrocene (m/z = 766.2530 for [FeC10DMS10] + ) was only observed in traces. Instead, mixtures of [FeC10DMS7H3] (m/z = 592.1711 for [FeC10DMS7H3] + ) and [FeC10DMS8H2] (m/z = 650.1946 for [FeC10DMS8H2] + ) as main products were obtained (Scheme 1, bottom) in presence of DMSCl indicating that the nucleophilicity of the Grignard species {FeC10DMSn(MgBr)10-n} (n = 8, 9, 10) is decreased with every DMS group attached to it. Therefore, additional reactions were carried out with DMSOTf as a more electrophilic silylation reagent. In the reactions including DMSOTf, however, silylation of attached DMS groups takes place rather than the formation of the persilylferrocene, causing oligomerization of the attached silyl groups as well as polymerization of the solvent.