Ferrociphenols (FCs) and their oxidized, electrophilic quinone methide metabolites (FC-QMs) are organometallic compounds related to tamoxifen that exhibit strong antiproliferative properties. To evaluate the reactivity of FC-QMs towards cellular nucleophiles, we studied their reaction with selected thiols. A series of new compounds resulting from the addition of these nucleophiles, the FC-SR adducts, were thus synthesized and completely characterized. Such conjugates are formed upon metabolism of FCs by liver microsomes in the presence of NADPH and thiols. Some of them exhibit antiproliferative properties comparable to those of their FC precursors. Under oxidizing conditions they either lead to their FC-QM precursors or to new quinone methides containing the SR moiety, FC-SR-QM. These results not only provide interesting data about the reactivity and mechanism of antiproliferative effects of FCs, but also open the way towards new series of organometallic anti-tumor compounds.