CRYSTAL AND MOLECULAR-STRUCTURE OF PROTONATED (N-PROPYL)-AMINOMETHYL FERROCENE, A PROTON-SENSITIVE REDOX-RESPONSIVE FRAGMENT

In order to rule out any possible 'chelate' iron-proton interaction wh ich could be responsible for the dramatic changes observed in the Fc()/Fc redox potential on proton addition in a series of N-substituted a minomethyl ferrocenes (4a-d), we report the results of electrochemical titration experiments with strong acids on the free amines in protic and aprotic solvents and the X-ray diffraction structure of (ferroceny lmethyl) propylammonium p-toluenesulfonate, [4aH][OTs]. Crystals of [4 aH][OTs] are orthorhombic, space group P2(1)2(1)2(1), with a = 11.919( 2), b = 21.313(3), c = 8.246(2) Angstrom, Z = 4. The conformation of t he FcCH(2)NH(2)C(3)H(7)(+) cation, which prevents any intramolecular i ron-proton interaction, seems imposed by the intermolecular N-H ... O hydrogen bonds that the amino H atoms form with oxygen atoms from p-to luenesulfonate anions. (C) 1998 Elsevier Science S.A.