Protonation-induced Intramolecular Electron Transfer in the Ferrocene-Quinone Conjugated System

the quinonoid compound linked to ferrocene by a 7C-conjugated spacer model provides insight into proton-coupled intramolecular electron transfer, because the redox potentials of the two molecules are similar and the redox potential of the quinonoid molecule can be readily controlled by external perturbation such as pro- 

1-FcAq [1-FvAqH] l,8-Fc2Aq [1,8-FcFvAqHf l,5-Fc2Aq [1,5-FcFvAqH] [l,5-FcFvAqH2f l,l -FcAq2 -1.85 (2e , Aq) 

The number of electrons for the reaction is one except otherwise stated in parentheses. 

The deprotonated form, 1-FcAq, shows reversible two-step 1 e reduction at = -1.26 and -1.71 V versus ferrocenium/ferrocene (Fc /Fc) derived from the anthraquinone moiety, and reversible 1 e oxidation at = 0.22 V due to the fer-rocenyl moiety in BU4NCIO4-CH2CI2 (Table 3.4). The first reduction potential shifts dramatically in the positive direction to E = -0.06 V, and the oxidation potential shifts moderately in the positive direction to E = 0.33 V in the protonation product, [1-FvAqH], whereas the second reduction potential is little changed. These results correspond to the structural changes in both ferrocenyl and anthraquinone moieties by protonation. 

Protonation reaction pathway of l,8-Fc2Aq and l,5-Fc2Aq The arrow - indicates conjugation between Fc and carbonyl groups. 

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Protonation-induced Intramolecular Electron Transfer in the Ferrocene-Quinone Conjugated System... 

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