Valentín Miranda-Soto

Evolution of iridium-based molecular catalysts during water oxidation with ceric ammonium nitrate.

Organometallic iridium complexes have been reported as water oxidation catalysts (WOCs) in the presence of ceric ammonium nitrate (CAN). One challenge for all WOCs regardless of the metal used is stability. Here we provide evidence for extensive modification of many Ir-based WOCs even after exposure to only 5 or 15 equiv of Ce(IV) (whereas typically 100-10000 equiv are employed during WOC testing). We also show formation of Ir-rich nanoparticles (likely IrO(x)) even in the first 20 min of reaction, associated with a Ce matrix. A combination of UV-vis and NMR spectroscopy, scanning transmission electron microscopy, and powder X-ray diffraction is used. Even simple IrCl(3) is an excellent catalyst. Our results point to the pitfalls of studying Ir WOCs using CAN.

Imidazol-2-yl complexes of Cp*Ir as bifunctional ambident reactants.

Loss of chloride ion from imidazol-2-yl complex 4a activates the H-H bond of dihydrogen or the C-H bond of acetylene, forming an Ir(III) N-heterocyclic carbene (NHC) complex (3b or 9). Deprotonation of Ir(III) hydride 4b gives one new species, formulated as Ir(I) carbene complex 5. Protonation or alkylation of 5 occurs at the metal, returning the Ir(III) core of 6a,b. Deprotonation of cationic NHC complex 3a gives neutral imidazol-2-yl analogue 4a; as seen by X-ray diffraction, the Ir-C bond in 3a is shorter than that in 4a. These and other comparisons and interconversions of NHC complexes with an NH function and related imidazol-2-yl species expand the potential of NHC complexes by showing their bifunctional character.

A Labile and Catalytically Active Imidazol‐2‐yl Fragment System

N-heterocyclic carbenes (NHCs) and their complexes are excellent catalysts for a broad array of organic transformations, where the NHC ligands impart useful electronic and steric properties to metal centers. In these systems, with commonly used ancilliary NHC ligands that are substituted at nitrogen atom(s) by alkyl, aryl, or other groups, all catalytic transformations take place at the metal center, which is stabilized and/or activated by the NHC ligand. However, transformations that may possibly involve both the metal center and at one ring nitrogen of the NHC ligand are much less common, 5c,e–g] and are limited to protic NHC complexes or their conjugated bases. Thus, the N H function of a protic NHC complex (A or D ; Scheme 1) could

Finding the Proton in a Key Intermediate of anti-Markovnikov Alkyne Hydration by a Bifunctional Catalyst

The secondary structure of a bifunctional catalyst positions a crucial reactive proton in the final intermediate of anti-Markovnikov alkyne hydration to give an aldehyde. NMR coupling and isotopic labeling studies elucidate the location of this proton and its involvement in hydrogen bonding.

Selective interaction of N,N-bis(aminobenzyl)naphthalenediimides with fluoride anion

Abstract In this work, the optical properties of N,N-bis(aminobenzyl)naphthalenediimides 2a–2d (BzNDIs) and their interaction with fluoride were studied. The results demonstrated that the amino group position in the benzyl substituent exerts an effect in the absorption and emission properties. Particularly, the N,N-bis(2-aminobenzyl)NDI 2b presented non-typical absorption and emission bands which indicate an intramolecular charge transfer from the amino phenyl group to the NDI core. As the concentration of 2b increases, the solution turns from colourless to a pale orange colour. The interaction of BzNDIs 2a–2d with anions was selective towards fluoride and the affinity was in the order para > ortho > meta with respect to the position of the amino group in the aminophenyl ring. Interestingly, the colour change in the solution of 2b upon addition of fluoride makes it a good candidate for a fluoride colorimetric detection. The voltammetry analysis indicates the ability of these molecules to accept two electrons, in consequence the interaction of two fluoride anions with the BzNDIs was observed.

Synthesis, crystal structure, DFT studies and photophysical properties of a copper(I)–tri­phenyl­phosphane complex based on trans-(±)-2,4,5-tris­(pyridin-2-yl)-2-imidazoline

The possibility of using less expensive and nontoxic metals, such as copper, as substitutes for more expensive heavy metals in the synthesis of new transition-metal complexes to be used as sensitizers in dye-sensitized solar cells (DSSCs) has stimulated research in this field. The novel photoluminescent copper(I) complex bis(triphenylphosphane-κP)[trans-(±)-2,4,5-tris(pyridin-2-yl)-2-imidazoline-κ2N2,N3]copper(I) hexafluorophosphate, [CuI(C18H15N5)(C18H15P)2]PF6, has been successfully synthesized and characterized by IR and 1H NMR spectroscopy, as well as by single-crystal X-ray diffraction and thermogravimetric analysis. The complex showed interesting photophysical properties, which were studied experimentally in solution and in the solid state by UV-Vis and fluorescence spectroscopy. Density functional theory (DFT) calculations with dichloromethane as solvent reproduced reasonably well the HOMO and LUMO orbitals of the title compound.

New fluorescent metal receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acid analogues with naphthalene fluorophore

Abstract In this manuscript is described a research related with two ditopic receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acids bearing a naphthyl (2a) and naphthylmethyl fluorophores (2b), which interact with metal ions. The fluorescence properties of both receptors were influenced by the connectivity with the amide group. The non-spaced receptor 2a presents an electron delocalisation from the amide to the naphthyl group having a broad red-shifted emission band and high quantum yield. The spaced receptor 2b presented a photo-induced electron transfer (PET) process from the amide to the naphthyl group, and a structured emission band is present at the UV region with low quantum yield. The different chemical structure influenced the fluorescent response used to analyse the coordination with metallic ions. The 2a receptor has an ON–OFF response because of the inhibition of the ICT process. The 2b receptor shows an OFF–ON response because of the inhibition of the PET process. Additional analytical studies by 1H-NMR and FTIR demonstrated the strong interaction of the amide and carboxylic functional groups with the metallic ions. Competitive experiments with EDTA showed that a very stable complexes are obtained between metallic ions and the new receptors.