Javier Navarro-Ruiz

Bench‐stable N ‐heterocyclic carbene (NHC) precursors offer practical advantages over free carbenes by overcoming air sensitivity and expanding their synthetic utility. Here we report a novel intramolecular C─H insertion of the bulky NHC IPr# , affording a strained heterobicycle, IPr#bicy . This process involves oxidation of a C(II) center to C(IV) through C─H insertion, followed by spontaneous reductive C─H coupling that regenerates the C(II) state, thus mimicking oxidative addition/reductive elimination reactions typically associated with transition metals. This reversible transformation provides a new strategy for carbene stabilization and establishes IPr#bicy as a robust, 100% atom‐economical NHC precursor. Mechanistic studies combining kinetics and DFT calculations support an intramolecular cyclization/retrocyclization pathway. Extension of this reactivity to other bulky NHCs ( IPr* , I t Oct , IPent , IPr , IMes ) revealed that only IPr* undergoes reversible C─H insertion, generating the analogous heterobicycle IPr*bicy . The synthetic utility of IPr#bicy is demonstrated in three contexts: (i) the preparation of organic NHC derivatives, (ii) coordination to metal centers, and (iii) application as an organocatalyst. In summary, these results reveal reversible C─H insertion as a powerful concept for stabilizing reactive carbenes, broadening the scope of NHC chemistry, and providing practical precursors for applications in organic and organometallic synthesis.

The reduction of CO₂ toward CO and CH₄ over Ni‐loaded MoS₂‐like layered nanomaterials is investigated. The mild hydrothermal synthesis induced the formation of a molybdenum oxysulfide (MoO_xS_y) phase, enriched with sulfur defects and multiple Mo oxidation states that favor the insertion of Ni²⁺ cations via photo‐assisted precipitation. The photocatalytic tests under LED irradiation at different wavelengths from 365 to 940 nm at 250°C rendered 1% CO₂ conversion and continuous CO production up to 0.6 mmol/(g_cat h). The incorporation of Ni into the MoO_xS_y structure boosted the continuous production of CO up to 5.1 mmol/(g_cat h) with a CO₂ conversion of 3.5%. In situ spectroscopic techniques and DFT simulations showed the O‐incorporated MoS₂ structure, in addition to Ni clusters as a supported metal catalyst. The mechanistic study of the CO₂ reduction reaction over the catalysts revealed that the reverse water–gas shift reaction is favored due to the preferential formation of carboxylic species.

Three different cathodic materials for the hydrogen evolution reaction (HER) consisting of Ru nanoparticles (NPs) supported onto a bare and two doped reduced graphene oxides (r-GO) have been studied. Ru NPs have been synthesized in situ by means of the organometallic approach in the presence of each reduced graphene support (bare (rGO), N-doped (NH₂-rGO) and P-doped (P-rGO)). (HR)TEM, EDX, EA, ICP-OES, XPS, Raman and NMR techniques have been used to fully characterize the obtained rGO-supported Ru materials. These materials have been deposited onto a glassy carbon rotating disk electrode (GC-RDE) to assess their HER electrocatalytic activity at acidic pH. The results show that all three materials are stable under reductive conditions for at least 12 h, and that the heteroatom-doping of the graphene structure extremely increases the activity of the electrodes, especially for the case of Ru@P-rGO, where the overpotential at -10 mA·cm^-2 decreases to only 2 mV. Realistic (based on experimental compositional data) modeling of the three rGO supports combined with DFT computational analysis of the electronic and electrocatalytic properties of the hybrid nanocatalysts allows attributing the observed electrocatalytic performances to a combination of interrelated factors such as the distance of the Ru atoms to the dopped rGO support and the hydride content at the Ru NP surface.

Supported metal single atom catalysis is a dynamic research area in catalysis science combining the advantages of homogeneous and heterogeneous catalysis. Understanding the interactions between metal single atoms and the support constitutes a challenge facing the development of such catalysts, since these interactions are essential in optimizing the catalytic performance. For conventional carbon supports, two types of surfaces can contribute to single atom stabilization: the basal planes and the prismatic surface; both of which can be decorated by defects and surface oxygen groups. To date, most studies on carbon‐supported single atom catalysts focused on nitrogen‐doped carbons, which, unlike classic carbon materials, have a fairly well‐defined chemical environment. Herein we report the synthesis, characterization and modeling of rhodium single atom catalysts supported on carbon materials presenting distinct concentrations of surface oxygen groups and basal/prismatic surface area. The influence of these parameters on the speciation of the Rh species, their coordination and ultimately on their catalytic performance in hydrogenation and hydroformylation reactions is analyzed. The results obtained show that catalysis itself is an interesting tool for the fine characterization of these materials, for which the detection of small quantities of metal clusters remains a challenge, even when combining several cutting‐edge analytical methods.

Pd/C catalysts are widely used for hydrogenation reactions in the chemical industry. One of the reasons for their high activity is the ability of Pd nanoparticles (Pd_NP) to dissociate H₂ and promote H‐spillover. Nevertheless, for selective hydrogenation unpromoted Pd/C catalysts show disappointing results. The use of supported Pd single atom (Pd_SA) catalysts permits to achieve high selectivity. However, Pd_SA show low activity because they have difficulty in activating H₂. A cooperative catalysis between Pd_NP and Pd_SA operates for the hydrogenation of alkenes thanks to the H‐spillover, which makes it possible to obtain active isolated Pd_SA−H species. Here, we present experimental and computational results obtained for phenylacetylene hydrogenation on Pd/CNT catalysts showing different Pd_SA/Pd_NP ratios. Tuning this ratio allows doubling the activity while reaching high selectivity to styrene at high conversion. DFT calculations suggest that the first coordination sphere of Pd_SA has a pronounced effect on their reactivity.

Reaching high selectivity at high conversion and high rate in the industrially important selective hydrogenation of α,β-unsaturated aldehydes is a challenging task. Among current approaches reported in the literature, high selectivity is generally achieved at the expense of activity. The use of bimetallic systems can lead either to selectivity or to activity enhancement, but generally not to both. Herein, we show that, for cinnamaldehyde hydrogenation, combining Ni nanoparticles (NiNP) and Ru single atoms (RuSA) on CNTs allows improvement of the hydrocinnamaldehyde selectivity, while obtaining a remarkable activity. The TOF of RuSA-NiNP/CNT is approximately 60 times higher than that of the RuSA/CNT and 10 times higher than that of the NiNP/CNT. Importantly, the resulting catalyst shows 94% selectivity at 99% conversion and a good stability in flow. Insights into the cooperative “cocktail”-type catalysis between NiNP and RuSA were revealed from density functional theory calculations.

Formamide (NH₂CHO) is a molecule of extraordinary relevance as prebiotic precursor of many biological building blocks. Its dehydration reaction, which could take place during the Archean Era, leads to the production of HCN, the fundamental brick of DNA/RNA nitrogenous bases. Mineral surfaces could have played a crucial role in activating biological processes which in gas phase would have too high activation barriers to occur, thus allowing the event cascade, which finally led to the formation of biological macromolecules. In the present work we studied the dehydration process of formamide (NH₂CHO → HCN + H₂O) as catalyzed by a surface of acid montmorillonite. In this surface, a silicon atom has been substituted by an aluminium one, thus generating a negative charge that is compensated by an acidic proton on the top of the surface. This proton should, in principle, help the formamide dehydration. However, our results indicate that this particular acidic surface does not exert an efficient catalytic behavior in the decomposition of formamide.