Modulation of the electronic communication between two equivalent ferrocene centers by proton transfer, solvent effects and structural modifications

Abstract

A series of six new dinuclear ferrocene compounds with the bridging fragment CH2-N(R)-CH2 were prepared and characterized. Bis(ferrocenylmethyl)-t-butylamine (1), bis(ferrocenylmethyl)-isopropylamine (2), bis(ferrocenylmethyl)-hexylamine (3), bis(ferrocenylmethyl)-p-methoxyaniline (4), bis(ferrocenylmethyl)aniline (5) and bis(ferrocenylmethyl)-p-nitroaniline (6), as well as the quaternized amine bis(ferrocenylmethyl)hexylmethylammonium hexaflurophosphate (3+·PF6-), were investigated using electrochemical techniques, 1H NMR spectroscopy and single crystal X-ray diffraction analysis. The voltammetric data indicate that the extent of electronic communication between the equivalent ferrocene centers increases in low polarity solvents and when bulky aliphatic groups are covalently attached to the central tertiary nitrogen. The observed experimental data are consistent with through-space communication effects, essentially electrostatic in nature. The extent of electronic communication can be modulated by reversible and irreversible reactions in the solution phase. Protonation or methylation of the tertiary nitrogen in the middle of the bridge disrupts the electronic communication between the ferrocene residues. © 2001 Elsevier Science Ltd.