Communication pubs.acs.org/IC
Formation, Characterization, and Reactivity of a Nonheme Oxoiron(IV) Complex Derived from the Chiral Pentadentate Ligand asN4Py Dóra Lakk-Bogáth,† Róbert Csonka,† Gábor Speier,† Marius Réglier,‡ A. Jalila Simaan,*,‡ Jean-Valère Naubron,§ Michel Giorgi,§ Károly Lázár,∥ and József Kaizer*,† †
Department of Chemistry, University of Pannonia, 8201 Veszprém, Hungary Aix Marseille Université, CNRS, Centrale Marseille, iSm2 UMR 7313, 13397 Marseille, France § Aix Marseille Université, CNRS, Centrale Marseille, Spectropole FR1739, 13397 Marseille, France ∥ Research Centre for Energy, Hungarian Academy of Sciences, H-1525 Budapest, Hungary ‡
S Supporting Information *
chemistry of nitrogen-rich pentadentate ligands has received much attention. These ligands have demonstrated the ability to stabilize high-valent metal centers and participate in hydrogenatom-transfer and oxygen-atom-transfer (OAT) reactions.11 Despite such attention, the element of chirality has been noticeably absent in these ligands. There are only a few examples of chiral pentadentate ligands reported that contain similar nitrogen-rich donor sets.12 As a synthetic model of nonheme monoiron enzymes, a new chiral pentadentate ligand and its iron(II) complex were synthesized, characterized, and used as a precursor of chiral oxoiron(IV) species. The formation kinetics, characterization, reactivity, and (enantio)selectivity of this intermediate in an OAT reaction were investigated in detail and compared to a similar pentadentate ligand-containing system. A chiral N4Py-type ligand, N,N-bis(2-pyridylmethyl)1,2-bis(2-pyridyl)ethylamine (asN4Py), was synthesized and characterized by NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and X-ray crystallography (Figures S1−S4). Chiral separation of the racemic ligand has been carried out by high-performance liquid chromatography in a heptane/ ethanol (50/50) mixture, and electronic circular dichroism was used to establish the absolute configurations (+)-(S) and (−)-(R) of asN4Py (Table S1 and Figures S5 and S6). Using the racemic mixture, asN4Py forms the monomeric iron(II) complex [FeII(asN4Py)(CH3CN)]2+ (1; Figure 1). The structure of 1·2ClO4 was revealed by X-ray structure analysis (Figure 1 and Figure S7). The distances and angles of the iron(II) core in 1 are almost equivalent to those in similar iron(II) complexes of N4Py-type ligands. The replacement of a pyridyl arm by a 2-pyridylethyl arm results in a lengthening of the Fe−Ndiv, Fe−Namine, and Fe−NMeCN bond distances by 0.07, 0.011, and 0.029 Å, respectively, with respect to [FeII(N4Py)(MeCN)](ClO4)2. The short Fe−N bond lengths (1.9−2.0 Å) are in agreement with the presence of a low-spin iron(II) center in 1·2ClO4, as observed for [FeII(N4Py)(MeCN)](ClO4)2 and some previously reported pentadentate ligand containing iron(II) complexes (Tables S2−S4).11d,13 The ESI-MS spectrum of 1·2ClO4 in acetonitrile (MeCN) exhibited three major peaks
ABSTRACT: The chiral pentadentate low-spin (S = 1) oxoiron(IV) complex [FeIV(O)(asN4Py)]2+ (2) was synthesized and spectroscopically characterized. Its formation kinetics, reactivity, and (enantio)selectivity in an oxygen-atom-transfer reaction was investigated in detail and compared to a similar pentadentate ligand-containing system. ononuclear nonheme iron enzymes,1 including the α-keto acid dependent taurin dioxygenase,2 prolyl-4-hydroxy3 lase, clavaminate synthase,4 and 4-hydroxyphenylpyruvate dioxygenase,5 the ascorbate-dependent 1-aminocyclopropane1-carboxylate oxidase,6 as well as the pterin-dependent phenylalanine and tyrosine hydroxylase,7 are responsible for a broad range of oxidative reactions (hydroxylation, desaturation, epoxidation, oxygenation, etc.), where the formation of FeIVO species frequently involved reactive intermediates.8 Chiral sulfoxides are found in many biologically active compounds as subunits. Bioinspired chemistry may help to work out a highly efficient catalytic system for the asymmetric oxidation of sulfides to sulfoxides. Chiral iron porphyrins with ArIO or ROOH as a terminal oxidant have proven to be efficient catalysts for sulfoxidation in high yields (67−84%), but the enantioselectivities were moderate (
