Florencia Vattier

Nitrous oxide (N ₂ O) is a significant contributor to climate change owing to its dual role as greenhouse gas and ozone-depleting molecule. Herein, the catalytic reduction of N ₂ O to N ₂ using methanol (MeOH) as a terminal reductant was investigated employing a series of Ru complexes supported by proton-responsive picoline- and lutidine-derived pincer ligands incorporating N-heterocyclic carbene donors (CNC and CNN). Among the complexes examined, a Ru catalyst featuring a picoline-derived CNN ligand incorporating a secondary amine functionality displayed the highest activity, achieving turnover numbers (TONs) up to 417 after 72 h, in the reduction of N ₂ O to N ₂ . Under catalytic conditions, the formation of metal nanoparticles from this catalytic precursor was observed. These nanoparticles were independently synthesized and found to be catalytically active in the reduction of N ₂ O with MeOH. Finally, control experiments further demonstrated that both homogeneous and nanoparticle species contribute to the overall catalytic process, participating in the methanol reforming and N ₂ O reduction steps.

A manganese( i ) complex featuring a CNN pincer ligand incorporating two acidic sites serves as catalyst for ester hydrogenation.

A manganese(I) complex featuring a picoline-derived CNN pincer ligand with two acidic sites ‒the methylene linker and a secondary amino group‒ has been synthesized. In the presence of an alkoxide base, this complex catalyzes the hydrogenation of esters to the corresponding alcohols under relatively mild conditions (1.0 mol% Mn, 10 mol% KOR, 20 bar H2, 110 oC). Stoichiometric reactions of the Mn(I) precursor with an excess of strong base (3 equiv of KHMDS or KOtBu) yield a manganate(I) species (Mn-CNN**) via the deprotonation of both acidic sites of the pincer ligand. X-ray photoelectron spectroscopy (XPS) evinces that the Mn-CNN** complex features a Mn center coordinated by a dianionic CNN** ligand. Finally, detailed DFT calculations were carried out on the two key steps of the catalytic cycle ‒H2 activation and hydride transfer to the ester substrate‒ considering neutral and anionic manganese species. The results indicate that ester hydrogenation proceeds via a Mn(I)-mediated anionic–dianionic manifold, where ligand deprotonation facilitates both H2 cleavage and hydride transfer.

H/D exchange in N-heterocycles with D ₂ gas was investigated using ultrasmall Ru/Co nanoparticles stabilized by NHC ligands. Catalytic performance is governed by both nanoparticle composition and substrate nature.

Nickel nanoparticles (Ni·MIC) stabilized with mesoionic 1,2,3-triazolylidene (MIC) ligands were prepared via decomposition of the [Ni(COD)₂] (COD = 1,5-cyclooctadiene) complex with H₂ (3 bar) in the presence of 0.2 or 0.5 equiv of ligand. The obtained monodisperse and small-sized (3.2-3.8 nm) nanoparticles were characterized by high-resolution transmission electron microscopy (TEM, HRTEM) and inductively coupled plasma (ICP) analysis. Further analysis of the nickel nanoparticles by X-ray photoelectron spectroscopy (XPS) demonstrated the coordination of the MIC ligands to the metal surface. Finally, the Ni·MIC nanoparticles were applied in the isotopic H/D exchange in hydrides of group 14 elements (Si, Ge, Sn) using D₂ gas under relatively mild conditions (1.0-1.8 mol % Ni, 1 bar D₂, 55 °C). High and chemoselective deuterium incorporation at the E-H (E = Si, Ge, Sn) bond in these derivatives was observed.

Tb-doped TiO₂ (anatase) micro-hollow spheres (HSs) with nano-shells, in the range 0.00–3.00 at.% Tb, were successfully synthesized by a simultaneous chemical implantation route of both Ti and Tb cations from chlorides to a poly-styrene (PST)-co-poly-divinyl benzene (PDVB) sacrificial template, followed by controlled hydrolysis and polycondensation reactions. After water addition to the mixture of the precursors with the template, a decrease in the intensity and a shift to lower wavenumbers of the C=O absorption band in the IR spectra can indicate not only the anchoring of Ti and Tb ions to the carbonyl group of the template but also the hydrolysis of the implanted precursors. This latter process can involve a proton attack on the Ti–Cl, Tb–Cl and C=O bonds, the occupation of a vacant site by a water molecule, and then the dissociation of the dangling Ti–Cl, Tb–Cl ligands and C=O bonds. It gives rise to Ti_1−xTb_x[(OH)_4−uCl_v]@PST–PDVB and Ti_1−xTb_x[(OH)_4−y]@PST–PDVB complexes (x = 0.00, 0.0012, 0.0170 and 0.030). Finally, polycondensation of these species leads to Ti_1−xTb_xO_2−w′@PST–PDVB compounds. After subsequent thermal removal at 550 °C of the template, the IR bands of the core (template) totally vanished and new bands were observed in the 400–900 cm⁻¹ region which can be attributed to the metalloxane bondings (M–O, M’–O, M–O–M, M–O–M’ and/or M’–O–M’, being M and M’ = Ti and Tb, respectively, i.e., mainly vibration modes of anatase). Then, micron-sized HSs of TiO₂ and Tb-doped-TiO₂ (anatase) were obtained with nano-shells according to field emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) observations. Furthermore, X-ray photoelectron spectroscopy (XPS) measurements confirmed the presence of Tb⁴⁺ (38.5 and 41.2% for 1.70 and 3.00 at.% Tb, respectively) in addition to Tb³⁺ in the resulting HSs, with increasing Tb⁴⁺ content with both Tb doping and higher calcination temperatures. Then, these HSs can be considered as rare earth (RE) co-doped systems, at least for 1.70 and 3.00 at.% Tb contents being the transition to rutile phase favored by Tb doping for those compositions. Finally, diffusion of Tb from the inner parts to the surface of the HSs with the calcination treatments was also observed by XPS.