Stéphane Torelli

Dinuclear Zinc(II)−Iron(III) and Iron(II)−Iron(III) Complexes as Models for Purple Acid Phosphatases

The heterodinuclear ZnIIFeIII complex 1 and the isostructural FeIIFeIII complex 2 with the dinucleating ligand from 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methoxyphenol (HBPMOP, 3) were prepared and characterized by X-ray crystallography. Solution studies (UV/Vis spectroscopy; electrochemistry) are described. A pH-induced change in the coordination spheres of the metal centers is seen. These complexes serve as models for the mixed-valence oxidation state in purple acid phosphatases. The cleavage acceleration of the activated phosphodiester 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) was investigated in acetonitrile/water (1:1) in the presence of complexes of the ligand BPMOP and its methyl analogue BPMP with regards to its dependence on the pH value. At the optimum pH value (8.5 ± 0.2), the ZnIIFeIII complex from BPMOP shows a 2-fold higher rate acceleration compared with that of the complex containing BPMP. The diiron complex from BPMOP is 4-fold more reactive than the homologous complex from BPMP. The heterodinuclear ZnIIFeIII catalysts are at least 10-fold more reactive than the homonuclear FeIIFeIII catalysts.

Spectroscopic and computational studies of (μ-Oxo)(μ-1, 2-peroxo)diiron(III) complexes of relevance to nonheme diiron oxygenase intermediates

With the goal of gaining insight into the structures of peroxo intermediates observed for oxygen-activating nonheme diiron enzymes, a series of metastable synthetic diiron(III)-peroxo complexes with [Fe(III)(2)(mu-O)(mu-1,2-O(2))] cores has been characterized by X-ray absorption and resonance Raman spectroscopies, EXAFS analysis shows that this basic core structure gives rise to an Fe-Fe distance of approximately 3.15 A; the distance is decreased by 0.1 A upon introduction of an additional carboxylate bridge. In corresponding resonance Raman studies, vibrations arising from both the Fe-O-Fe and the Fe-O-O-Fe units can be observed. Importantly a linear correlation can be discerned between the nu(O-O) frequency of a complex and its Fe-Fe distance among the subset of complexes with [Fe(III)(2)(mu-OR)(mu-1,2-O(2))] cores (R = H, alkyl, aryl, or no substituent). These experimental studies are complemented by a normal coordinate analysis and DFT calculations.

Design of iron chelators: syntheses and iron (III) complexing abilities of tripodal tris-bidentate ligands.

The interest in synthetic siderophore mimics includes therapeutic applications (iron chelation therapy), the design of more effective agents to deliver Fe to plants and the development of new chemical tools in order to study iron metabolism and iron assimilation processes in living systems. The design of ligands needs a rational approach for the understanding of the metal ion complexing abilities. The octahedral arrangement of donor atoms is the most favourable geometry, allowing the maximum possible distance between their formal or partial negative charges. Hexadentate chelators, usually of the tris-bidentate type, can accommodate the metal coordination sphere and are well-suited to obtain high pFe values. The first part of this review is dedicated to selected synthetic routes, taking into account (i) the nature of the chelating subunits, connecting groups and spacers, (ii) the water-solubility and hydrophilic/lipophilic balance, (iii) the chirality and (iv) the possibility of grafting probes or vectors. In the second part, we discuss the role of the molecular design on complexing abilities (thermodynamics and kinetics). The bidentate 8-hydroxyquinoline moiety offers an alternative to the usual coordinating hydroxamic acids, catechols and/or α-hydroxycarboxylic acids groups encountered in natural siderophores. The promizing results obtained with the tris-hydroxyquinoline-based ligand O-TRENSOX are summarized. O-TRENSOX exhibits a high and selective affinity for Fe(III) complexation. Its efficiency in delivering Fe to plants, iron mobilization, cell protection, and antiproliferative effects has been evidenced. Other chelators derived from O-TRENSOX (mixed catechol/8-hydroxyquinoline ligands, lipophilic ligands) are also described. Some results question the relevance of partition coefficients to foresee the activity of iron chelators. The development of probes (fluorescent, radioactive, spin labelled) based on the O-TRENSOX backbone is in progress in order to get insights in the complicated iron metabolism processes.

A Ruthenium(II)–Copper(II) Dyad for the Photocatalytic Oxygenation of Organic Substrates Mediated by Dioxygen Activation

Dioxygen activation by copper complexes is a valuable method to achieve oxidation reactions for sustainable chemistry. The development of a catalytic system requires regeneration of the Cu(I) active redox state from Cu(II). This is usually achieved using extra reducers that can compete with the Cu(II)(O2) oxidizing species, causing a loss of efficiency. An alternative would consist of using a photosensitizer to control the reduction process. Association of a Ru(II) photosensitizing subunit with a Cu(II) pre-catalytic moiety assembled within a unique entity is shown to fulfill these requirements. In presence of a sacrificial electron donor and light, electron transfer occurs from the Ru(II) center to Cu(II). In presence of dioxygen, this dyad proved to be efficient for sulfide, phosphine, and alkene catalytic oxygenation. Mechanistic investigations gave evidence about a predominant (3)O2 activation pathway by the Cu(I) moiety.

N2O reduction at a dissymmetric {Cu2S}-containing mixed-valent center

Through our bio-inspired approach toward replicating nitrous oxide reductase (N2Or) activity, treatment of the LMe(MAM)S–S ligand with [Cu(CH3CN)4](OTf) (OTf = trifluoromethanesulfonate ion) leads to the isolation of a new dissymmetric mixed-valent (MV) dicopper(II,I) [2·(H2O)(OTf)]+ containing a {Cu2S} core with labile triflate and water molecules at the copper centers. Whilst [2·(H2O)(OTf)]+ is prone to ligand exchange under particular conditions, a raft of spectroscopic investigations, combined with theoretical calculations demonstrate that its structure is retained in acetone solution. Compared to our previously reported inactive parent complex [1] (Angew. Chem. Int. Ed., 2010, 49 (44), 8249–8252) featuring a symmetric and saturated coordination sphere (N and S atoms from the ligand), [2·(H2O)(OTf)]+ is reactive towards nitrous oxide in acetone. Spectroscopic and theoretical studies combined with kinetic measurements show that exchangeable positions are required for N2O interaction. The isolation of the final product and its characterization by X-ray crystallography as a doubly bridged (μ-thiophenolato)(μ-hydroxo) dicopper(II) species [3·(μ-OH)(OTf)2] help to support the proposed reaction pathway. Implications for N2Or mechanism are discussed.

Heterodinuclear Cu(II)Zn(II) complexes: 19F NMR as a versatile tool to control the synthesis

Abstract The dinucleating ligands 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (H-BPMP) and 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-fluorophenol (H-BPFP) were used to synthesize heterodinuclear (μ-phenoxo)(μ-hydroxo) Cu(II)Zn(II) complexes. The labeled ligand with a fluorine atom allows the use of 19F NMR spectroscopy, which turned to be a rapid and powerful tool to tune the synthesis of the heterodinuclear paramagnetic complex [CuZnBPFP(μOH)](ClO4)2 and avoid mixing of complexes with statistical distribution. When applied to the non-fluorinated ligand, this experimental procedure leads to prepare and isolate easily the complex [CuZnBPMP(μOH)](ClO4)2. The X-ray structure is described.

Redox-Innocent Metal-Assisted Cleavage of S–S Bond in a Disulfide-Containing Ligand

Due to their redox capabilities, thiols have an important role in biological oxidative/reductive processes through the formation of disulfides or their oxidation to into sulfenic, sulfinic, or sulfonic derivatives being also relevant for specific enzyme activities. The mechanisms of these biological pathways often involve metal ion(s). In this case, deciphering metal-assisted transformation of the S-S bond is of primary interest. This report details the reactivity of the disulfide-containing 2,6-bis[(bis(pyridylmethyl)amino)methyl]-4-methylmercaptophenyldisulfide (L(Me(BPA)S-S)) ligand with Cu(II) using different experimental conditions (anaerobic, H2O-only, H2O/O2, or O2-only). Crystallographic snapshots show the formation of tetranuclear disulfide, dinuclear sulfinate, and sulfonate complexes. Mechanistic investigations using Zn(II) as control indicate a non-metal-redox-assisted process in all cases. When present, water acts as nucleophile and attacks at the S-S bond. Under anhydrous conditions, a different pathway involving a direct O2 attack at the disulfide is proposed.

Valence Localization at a Bio‐inspired Mixed‐Valent {Cu2S}2+ Motif upon Solvation in Acetonitrile: Effect on Nitrous Oxide Reductase (N2Or) Activity

We demonstrate, based on experimental and theoretical evidence, that the isolated [2(CH3 CN)2 ]2+ complex prepared in CH3 CN and containing a mixed-valent {Cu2II,I S} core evolves towards a new [2(CH3 CN)3 ]2+ species upon solvation in CH3 CN. Unlike its type III structural analogue [2(H2 O)(OTf)]+ active toward N2 O reduction, this new type I compound is inactive. This outcome opens new perspectives for a rational for N2 O activation using bio-inspired Cu/S complexes, especially on the role of the valence localization/delocalization and the Cu-Cu bond on the reactivity.