Iron Coordination Chemistry with New Ligands Containing Triazole and Pyridine Moieties. Comparison of the Coordination Ability of the N‑Donors

• Published in: Inorganic chemistry 2013-01, Vol.52 (2), p.691-700
• Main Authors: Ségaud, Nathalie, Rebilly, Jean-Noël, Sénéchal-David, Katell, Guillot, Régis, Billon, Laurianne, Baltaze, Jean-Pierre, Farjon, Jonathan, Reinaud, Olivia, Banse, Frédéric
• Format: Article
• Language: English
• Subjects: Catalysis; Coordination Complexes - chemistry; Iron - chemistry; Ligands; Molecular Structure; Nitrogen Compounds - chemistry; Pyridines - chemistry; Triazoles - chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic301834x

We report the synthesis, characterization, and solution chemistry of a series of new FeII complexes based on the tetradentate ligand N-methyl-N,N′-bis(2-pyridyl-methyl)-1,2-diaminoethane or the pentadentate ones N,N′,N′-tris(2-pyridyl-methyl)-1,2-diaminoethane and N,N′,N′-tris(2-pyridyl-methyl)-1,3-diaminopropane, modified by propynyl or methoxyphenyltriazolyl groups on the amino functions. Six of these complexes are characterized by X-ray crystallography. In particular, two of them exhibit an hexadentate coordination environment around FeII with two amino, three pyridyl, and one triazolyl groups. UV–visible and cyclic voltammetry experiments of acetonitrile solutions of the complexes allow to deduce accurately the structure of all FeII species in equilibrium. The stability of the complexes could be ranked as follows: [L5FeII-py]2+ > [L5FeII–Cl]+ > [L5FeII-triazolyl]2+ > [L5FeII-(NCMe)]2+, where L5 designates a pentadentate coordination sphere composed of the two amines of ethanediamine and three pyridines. For complexes based on propanediamine, the hierarchy determined is [L5FeII–Cl]+ > [L5FeII(OTf)]+ > [L5FeII-(NCMe)]2+, and no ligand exchange could be evidenced for [L5FeII-triazolyl]2+. Reactivity of the [L5FeII-triazolyl]2+ complexes with hydrogen peroxide and PhIO is similar to the one of the parent complexes that lack this peculiar group, that is, generation of FeIII(OOH) and FeIV(O), respectively. Accordingly, the ability of these complexes at catalyzing the oxidation of small organic molecules by these oxidants follows the tendencies of their previously reported counterparts. Noteworthy is the remarkable cyclooctene epoxidation activity by these complexes in the presence of PhIO.