FACILE SYNTHESIS OF FERROCENE BISCROWN ETHERS AND FERROCENE CRYPTANDS- NMR COMPLEXATION STUDIES AND THE REDOX-SWITCHED BONDING OF H+ AND NA+

The reaction of 1,1'-ferrocenylene-bis(methylenepyridinium) tosylate c hloride (1) with aza-x-crown-y (x/y = 12/4; 15/5; 18/6) gives the thre e novel ferrocene biscrown ethers 1,1'-ferrocenylene-bis(methylene-aza -x-crown-y) (x/y = 12/4, 2; 15/5, 3; 18/6, 4). The reaction of 1 with diaza-18-crown-6 represents a new and simple route to the known ferroc ene cryptands ene(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane)] (5) a nd ene(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane)] (6). The solid-s tate structure of 5 is described. The ferrocene bridge compresses the diaza crown ether leading to an internitrogen distance of 458 pm. The stoichiometry of Na+ and K + complexes with 2 and 3 in CD3CN determine d in NMR titration experiments suggests the formation of Na+ and K+ cr own ether sandwich complexes in solution. Cyclic voltammograms of 2 an d 5 in the presence of varying amounts of H+ and Na+ have been recorde d. The redox potential of ferrocene is shifted by + 180 mV in the case of 5 . Na + and up to +600 mV in the case of 5 . H+H+ relative to 5, but only by +70 mV with 2 . Na+ and 2. The protonation of 5 give rises to several isomers (exo and endo protonation) which differ significan tly in their redox potential. The extremely large positive shift of th e oxidation potential of the diprotonated ferrocene cryptand correspon ds to an increase in the acidity of 5 . H+H+ upon oxidation by more th an ten orders of magnitude and makes this system a candidate for the d irected membrane transport of protons.