Ferrocifen is a potent alternative to tamoxifen, the classic antiestrogenic breast cancer drug, combining simultaneous increased antiestrogenicity and cytotoxicity against cells not expressing the estrogen receptor. The currently proposed mechanism involves oxidation at the ferrocene (Fe(II) to Fe(III)), letting the phenolic proton be easily abstracted by a weak base. This creates a neutral phenoxy radical, which may then be delocalized over the molecular framework, namely onto the carbon alpha to the ferrocene, resulting in a quinone methide. To confirm the presence of a delocalized carbon-centered radical, we have created a number of oxidized ferrocenylmethylidenes with varying levels of conjugation. Preliminary X-band electron paramagnetic resonance studies show both definitive carbon-centered radicals (g = 1.9-2.0) with peak widths of ~150 gauss and iron-centered radicals  (g = 4.0-4.2) that have intensities inversely related to temperature.

Evidence for a carbon-centered radical delocalized over a weakly-conjugated molecular framework in ferrocenylmethylidines

243rd National Meeting (2012)

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