Ferrocene-Fused Acenequinones: Synthesis, Structure and Reaction Chemistry

The synthesis of anti-[1.1](2,17)(6,13)ferrocenophane-1,12-dione (2) is discussed. By addition of LiAlH4, NaBH4 or Wittig's reagent only one keto group reacted to give HO- or (c) C3H4-functionalized [1.1](2,17)(6,13)ferrocenophan-12-hydroxy-1-one (3) and [1.1](2,17)(6,13)ferrocenophan-12-cyclopropane-1-one (4). Exchange of CO by CS groups is possible upon addition of Lawesson's reagent to 2 forming [1.1](2,17)(6,13)ferrocenophan-1,12-dithioketone (5). Theoretical studies confirm the different reactivities of the CO groups. Electrochemical studies on 2-5 showed separated reversible one-electron events for 2-4 (125-925 mV) and an irreversible one for 5. The ferrocenyls in 4 are easier to oxidize, due to their higher electron-richness. In 2 a larger redox separation comes about suggesting a stronger intermetallic interaction between Fe-II/Fe-III in the mixed-valent species. In situ UV-vis/NIR studies confirm that 2 is a weak coupled class II system according to the classification of Robin and Day. Compounds 3 and 4 display electrostatic interactions among the ferrocenyls as oxidation progresses.