Carbon‐Nanotube‐Appended PAMAM Dendrimers Bearing Iron(II) α‐Keto Acid Complexes: Catalytic Non‐Heme Oxygenase Models

Iron(II)-α-keto acid complexes of tridentate ligands on gold nanoparticles: the effect of ligand geometry and immobilization on their dioxygen-dependent reactivity

Two mononuclear nonheme iron(II)-benzoylformate (BF) complexes [(6Me₂-Me-BPA)Fe(BF)](ClO₄) (1a) and [(6Me₃-TPMM)Fe(BF)](ClO₄) (1b) of tridentate nitrogen donor ligands, bis((6-methylpyridin-2-yl)methyl)(N-methyl)amine (6Me₂-Me-BPA) and tris(2-(6-methyl)pyridyl)methoxymethane (6Me₃-TPMM), were isolated and characterized. The structural characterization of iron(II)-chloro complexes indicates that the ligand 6Me₂-Me-BPA binds to the iron(II) centre in a meridional fashion, whereas 6Me₃-TPMM behaves as a facial ligand. Both the ligands were functionalized with terminal thiol for immobilization on gold nanoparticles (AuNPs), and the corresponding iron(II) complexes [(6Me₂-BPASH)Fe(BF)(ClO₄)]@C₈Au (2a) and [(6Me₃-TPMSH)Fe(BF)(ClO₄)]@C₈Au (2b) were prepared to probe the effect of immobilization on their ability to perform bioinspired oxidation reactions. All the complexes react with dioxygen to display the oxidative decarboxylation of the coordinated benzoylformate, but the complexes supported by 6Me₃-TPMM and its thiol-appended ligand display faster reactivity compared to their analogues with the 6Me₂-Me-BPA-derived ligands. In each case, an electrophilic iron-oxygen oxidant was intercepted as the active oxidant generated from dioxygen. The immobilized complexes (2a and 2b) display enhanced O₂-dependent reactivity in oxygen-atom transfer reactions (OAT) and hydrogen-atom transfer (HAT) reactions compared to their homogeneous congeners (1a and 1b). Furthermore, the immobilized complex 2b displays catalytic OAT reactions. This study supports that the ligand geometry and immobilization on AuNPs influence the dioxygen-dependent reactivity of the complexes.

The Effects of Ultrasound Treatment of Graphite on the Reversibility of the (De)Intercalation of an Anion from Aqueous Electrolyte Solution

Low cycling stability is one of the most crucial issues in rechargeable batteries. Herein, we study the effects of a simple ultrasound treatment of graphite for the reversible (de)intercalation of a ClO₄^- anion from a 2.4 M Al(ClO₄)₃ aqueous solution. We demonstrate that the ultrasound-treated graphite offers the improved reversibility of the ClO₄^- anion (de)intercalation compared with the untreated samples. The ex situ and in situ Raman spectroelectrochemistry and X-ray diffraction analysis of the ultrasound-treated materials shows no change in the interlayer spacing, a mild increase in the stacking order, and a large increase in the amount of defects in the lattice accompanied by a decrease in the lateral crystallite size. The smaller flakes of the ultrasonicated natural graphite facilitate the improved reversibility of the ClO₄^- anion electrochemical (de)intercalation and a more stable electrochemical performance with a cycle life of over 300 cycles.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Catalytic O2 activation with synthetic models of α-ketoglutarate dependent oxygenases

An iron complex bearing the facially capping tridentate 1,4,7-triazacyclononane ligand mimics structural and functional features of alpha-ketoglutarate (α-KG) dependent enzymes, and engages in enzyme-like catalytic O2 activation coupled to α-ketoacid decarboxylation, oxygenating sulfides. This system constitutes a rare case of non-enzymatic catalytic O2 activation, cycling between FeII and FeIV(O).