Di- and Mononuclear Iron Complexes of N,C,S-Tridentate Ligands Containing an Aminopyridyl Group: Effect of the Pendant Amine Site on Catalytic Properties for Proton Reduction

Abstract

A series of diiron complexes of N,C,S-tridentate ligands containing a 6-, 5-, or 4-amino-2-pyridyl group, [{Fe(μ-L-κ3N,C,S)(CO)2}Fe(CO)3] (2, L = o-apyBPT; 3, L = m-apyBPT; 4, L = p-apyBPT), was synthesized: apyBPT is a doubly deprotonated form of 3′-(amino-2″-pyridyl)-1,1′-biphenyl-2-thiol. Complexes 2–4 were converted to the mononuclear iron(II) complexes trans-[Fe(L-κ3N,C,S)(CO)(PMe2Ph)2] (6, L = o-apyBPT; 7, L = m-apyBPT; 8, L = p-apyBPT). In 2 and 6, the o-amino group is close to Fe bound to the aminopyridyl group. Cyclic voltammograms of 2–4 exhibit two consecutive one-electron reduction events, and catalytic current for proton reduction appears in the presence of acetic acid. The reduction potentials of 2–4 are similar to each other, while the overpotential for proton reduction with o-amino complex 2 is ca. 0.2 V lower than those with 3 and 4. In the mononuclear complexes 6–8, the redox potentials for the FeIII/FeII couple are dependent on the position of the amino group in the pyridine ring, which...