Improved synthesis of diethyl ferrocenylphosphonate, crystal structure of (FcPO3Et2)2 · ZnCl2, and electrochemistry of ferrocenylphosphonates, FcP(O)(OR)2, FcCH2P(O)(OR)2, 1,1′-fc[P(O)(OR)2]2 and [FcP(O)(OEt)2]2 · ZnCl2 (Fc = (η5C5H5)Fe(η5C5H4), fc = (η5C

An improved synthesis of diethyl ferrocenylphosphonate using the tBuLi/tBuOK system at low temperature is reported and the structure of [FcPO3Et2]2 · ZnCl2 complex is described. The electrochemical behaviour of FcP(O)(OEt)2, 1,1′-fc[P(O)(OEt)2]2, FcCH2P(O)(OEt)2, and their corresponding acids were compared. Each of them shows a reversible one-electron transfer reaction. Ferrocenylbisphosphonate is more difficult to oxidize than ferrocenylphosphonate due to the presence of two electron-withdrawing substituents. A methylene spacer between the ferrocenyl unit and the phosphonate group renders the compound easier to oxidize. The acids are easier to oxidize than the esters, and their salts, in which the phosphonate group behave as an electron-donating group, are even easier to oxidize than the ferrocene. The ferrocenylphosphonic acid may be, then, considered as a redox-active pH responsive molecule.