Metal‐free selective synthesis of α,β‐unsaturated aldehydes from alkenes and formaldehyde catalyzed by dimethylamine

α,β‐Unsaturated aldehydes are important building blocks for the synthesis of a wide range of chemicals, including polymers. The synthesis of these molecules from cheap feedstocks such as alkenes remains a scientific challenge, mainly due to the low reactivity of alkenes. Here we report a selective and metal‐free access to α,β‐unsaturated aldehydes from alkenes with formaldehyde. This reaction is catalyzed by dimethylamine and affords α,β‐unsaturated aldehydes in yields of up to 80 %. By combining Density Functional Theory (DFT) calculations and experiments, we elucidate the reaction mechanism which is based on a cascade of hydride transfer, hydrolysis and aldolization reactions. The reaction can be performed under very mild conditions (30–50 °C), in a theoretically 100 % carbon‐economical fashion, with water as the only by‐product. The reaction was successfully applied to non‐activated linear 1‐alkenes, thus opening an access to industrially relevant α,β‐unsaturated aldehydes from cheap and widely abundant chemicals at large scale

Unraveling the role of H 2 and NH 3 in the amination of isohexides over a Ru/C catalyst

The direct amination of biomass-derived isohexides with NH3 over a Ru/C catalyst was systematically investigated to understand the role of H2 and NH3 in the production of isohexide diamines vs aminoalcohols, i.e., the transformation of one or both OH-groups in isohexides into NH2 groups. Only aminoalcohols with an exo-OH group were generated starting from isosorbide, which contains both an exo-OH and an endo-OH group, while a moderate yield of diamines was obtained from isomannide with two endo-OH groups due to the higher reactivity of the latter. The main byproducts were identified, including a variety of N- and O-containing cyclic compounds, such as 2,5-dimethylpyrrolidine, that arise from a decomposition path driven by hydrolysis/hydrodeoxygenation of a tricyclic amine intermediate. By combining density functional theory calculations with microkinetics, NH3 was found to adsorb strongly on the catalyst surface and generate adsorbed NH2 and NH species with variable coverage depending on the temperature and the nominal H2/NH3 ratio. Isomerization of isohexides was greatly suppressed by adsorbed NH3. Meanwhile, adsorbed NH3 discouraged the formation of byproducts driven by competing side reactions promoted by H2. The H2/NH3 ratio, which conditions the distribution of NH2 and NH species on the Ru surface, influences drastically the catalytic performance

Etude théorique et expérimentale des sites défauts de l'alumine gamma partiellement hydratée (stabilité, réactivité envers des petites molécules et implications pour les catalyseurs à site unique)

Quand des alumines de transition (gamme et delta) sont prétraitées à hautes températures (au dessus de 400C) des défauts de surface avec une très forte acidité de Lewis sont formés. Leur densité atteint un maximum pour une température de prétraitement de 700C, puis elle décroit à plus haute température. En combinant des calculs DFT (réactivité et spectroscopie) et des expériences (IR, RMN, DRX et études de réactivité) la structure, la stabilité et la réactivité de ces site envers des petites molécules sondes (N2, H2 et CH4) ont été étudiés en tenant compte de l hydratation de la surface (densité d OH, qui décroit en fonction de la température de prétraitement). Cette approche a démontré que i) N2 s adsorbe sélectivement sur des sites AlIII (coordination), alors que H2 et CH4 sont dissociés sur des sites Al-O, en particulier sur les sites AlIII, avec formation d'espèces Al-H et Al-CH3 et de groupements OH (dissociation hétérolytique), ii) l hydratation a deux rôles: stabiliser la surface (110) qui contient ces sites AlIII et augmenter la basicité de certains atomes d oxygène de surface et en conséquence leur réactivité envers H2 et CH4. Cela explique la température optimale de prétraitement de 700C (la densité de AlIII est augmentée sans changement structural de l alumine; au dessus de cette température l alumine adopte une phase cristalline plus stable, théta et enfin alpha, qui ne présentent pas ces sites AlIII). Finalement, dans le contexte de systèmes catalytiques supportées sur alumine, ces défauts sont proposés comme élément clef pour la génération du site actif de CH3ReO3/alumine-gamma, un catalyseur de métathèse hautement efficace.When pre-treated at high temperatures (above 400 C), very strong Lewis acid sites ( defect sites ) are formed on transition alumina (gamma and delta) with an optimal site density found for pre-treatment temperatures of ca. 700 C, before their density decreases with higher thermal treatment. Combining periodic DFT calculations (reaction pathways and spectroscopy) and experiments (IR, NMR, XRD and reactivity studies) the structure, the stability and the reactivity of these sites towards small probe molecules (N2, H2 and CH4) was investigated taking into account hydration of the surface (OH density, which decreases function of thermal pre-treatment). This approach showed that i) N2 adsorbs selectively on AlIII sites (coordination), while H2 and CH4 are dissociated on Al-O sites, in particular on AlIII, to form Al-H and Al-CH3 species, respectively, along with OH-groups (heterolytic splitting). ii) Hydration has a dual role: stabilizing the (110) surfaces exhibiting these AlIII sites and increasing the basicity of some O atoms and thereby their reactivity towards H2 and CH4, hence the optimal pre-treatment temperature (increasing the AlIII site density without changing the structure of alumina; above 700 C alumina evolves towards theta and alpha phases, which do not present these sites). Finally, in the context of supported alumina systems, these defect sites are proposed to be the key to generate the active sites of CH3ReO3/gamma-Al2O3, a highly efficient alkene metathesis catalyst.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Simulating Solvation and Acidity in Complex Mixtures with First-Principles Accuracy: The Case of CH3SO3H and H2O2 in Phenol

We present a generally applicable computational framework for the efficient and accurate characterization of molecular structural patterns and acid properties in an explicit solvent using H2O2 and CH3SO3H in phenol as an example. To address the challenges posed by the complexity of the problem, we resort to a set of data-driven methods and enhanced sampling algorithms. The synergistic application of these techniques makes the first-principle estimation of the chemical properties feasible without renouncing to the use of explicit solvation, involving extensive statistical sampling. Ensembles of neural network (NN) potentials are trained on a set of configurations carefully selected out of preliminary simulations performed at a low-cost density functional tight-binding (DFTB) level. The energy and forces of these configurations are then recomputed at the hybrid density functional theory (DFT) level and used to train the neural networks. The stability of the NN model is enhanced by using DFTB energetics as a baseline, but the efficiency of the direct NN (i.e., baseline-free) is exploited via a multiple-time-step integrator. The neural network potentials are combined with enhanced sampling techniques, such as replica exchange and metadynamics, and used to characterize the relevant protonated species and dominant noncovalent interactions in the mixture, also considering nuclear quantum effects

Formation of Acrylates from Ethylene and CO2 on Ni Complexes: A Mechanistic Viewpoint from a Hybrid DFT Approach

International audienceThe most challenging step in the production of acrylates fromethylene and CO2 mediated by transition-metal complexes is the release ofthe acrylate from the metallalactone intermediate formed by coupling ofethylene and CO2. Recently, methyl acrylate formation was achieved fromnickelalactones by using methyl iodide (MeI) as the electrophile, and theyield was tuned with different amine and phosphine ligands. Modelingorganometallic catalysts with such large ligands accurately is a challenge forcomputational chemistry. A hybrid approach has been designed here bycoupling the double hybrid XYG3 and the hybrid B3LYP exchangecorrelation functionals, using the extended ONIOM scheme. This approachwas then applied to explore the role of the MeI electrophile for the formationof methyl acrylate from the initial nickelalactone complex and to rationalizethe effect of the ligands on the yield of methyl acrylate. We show that thechoice of ligand has little effect on the main productive pathway. However, it has a significant influence on side reactions, which compete with the productive pathway and are detrimental to methyl acrylate formation. Finally, the need for a very large overstoichiometry of MeI for a good yield of methyl acrylate is explained by the lower polarity of MeI, which avoids the stabilization of nonproductive intermediates. The nature of the limiting intermediates has been validated by comparing calculated and experimental vibrational spectra

Alcohol amination catalyzed by metal supported catalysts: The role of co-adsorbed species revealed by DFT studies

International audienceAmines are essential intermediates in chemical industries. To obtain them from alcohols is an alternative to the current processes that opens the road to the utilization of biomass-sourced alcohols. When catalyzed by metal supported catalysts, this reaction follows the H-borrowing mechanism. It starts with the alcohol dehydrogenation, followed by the addition of the amine on the intermediated aldehyde. Then, the resulting imine is hydrogenated into amine. This hydrogen transfer from the alcohol to the imine is an elegant route that limits the utilization of an external source of H2. In this context, we focus on the challenging amination of aliphatic alcohol by ammonia where the selectivity issue is prominent. In the quest of the best catalyst, we propose here to perform a detailed DFT study of the reaction mechanism on two metals, namely Pd and Ni. We based our study on the hydrogen-borrowing mechanism, using methanol as a simple model of alcohol. We computed the various possible reaction paths for the methanol dehydrogenation and then the imine hydrogenation using periodic DFT calculations with the PBE functional. Since the C-N coupling does not require any metal supported catalyst to proceed efficiently, we didn’t consider the elementary steps of this reaction. Comparing the energetic span obtained on Pd(111) and Ni(111), we predicted that Pd was slightly more active than Ni (1.26eV vs. 1.31eV). However, according to recent experimental studies[Shimizu et al. ACS Catal. 2013, 3, 112−117], Ni supported catalysts are clearly more active than Pd to perform the amination of aliphatic alcohol with ammonia. Since this reaction occurs in liquid phase but under a pressure of ammonia, we evaluate the coverage of ammonia at around 1/9ML at the working pressure and temperature (4 bar, 160°C). Then, we re-investigated the reaction paths including the effect of the co-adsorbed ammonia. On Pd(111), it pushes up slightly the first CH bond breaking in methanol and destabilizes also the strongly adsorbed amine leading to a reduced energetic span of 1.05eV. On Ni(111), the results are even more contrasted: ammonia stabilizes the initial OH scission transition state and strongly destablizes the amine. Then, the energetic span of the overall reaction is reduced to 0.78eV. Ni is then predicted being much more active than Pd. This is a clear example of the importance of co-adsorbed species on the activity of metallic catalysts in hydrogenation/dehydrogenation reactions

Ligand effects for the synthesis of acrylates from ethylene and CO2 on Ni complexes: a theoretical study

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Heterogeneously-catalyzed competitive hydroarylation/hydromination of norbornene with aniline in the presence of Aquivion® ionomer

The hydroarylation of alkenes with aniline is a reaction of high interest, in particular for the manufacture of polyurethanes. This reaction has been mostly investigated in the presence of homogeneous catalysts. So far, heterogeneous catalysts have been scarcely reported for this reaction, mainly due to their inherent low activity and deactivation during the course of the reaction. Here we report the catalytic performance of Aquivion® ionomer, a perfluorinated solid acid polymer, in the hydroarylation of norbornene with aniline. We show that Aquivion® ionomer was robust and can be recycled for at least 6 runs without any decrease of its catalytic performances. Our results also highlight that Aquivion® ionomer improves the propensity of aniline to react through its aromatic ring, thus yielding a higher proportion of hydroarylation products as compared to other tested homogeneous and heterogeneous catalysts

Visibility of Al Surface Sites of γ‑Alumina: A Combined Computational and Experimental Point of View

The nature of γ-alumina (γ-Al₂O₃) surface sites leaves many open questions today, and solid-state NMR spectroscopy has been proposed and used as a tool for assessing their structure. Here, we calculated ²⁷Al NMR parameters from first principles in periodic boundary conditions for a large number of Al sites with different coordination, potentially present on the alumina surface. The nature and accordingly the NMR parameters of these sites change with the level of hydroxylation and thereby the pretreatment temperature of γ-Al₂O₃. While the Al chemical shift is little affected by hydroxylation, the magnitude of the quadrupolar interaction at the Al nucleus is strongly correlated to hydroxylation, with high to very high quadrupolar coupling constant (<i>C</i>_Q) values (20–34 MHz) on the weakly hydrated major (110) termination, which contains highly reactive Lewis acidic “defect sites”, and gradual lowering to bulklike <i>C</i>_Q values of around 5 MHz on highly hydrated surfaces. In addition, we studied the effects of local symmetry on the EFG tensor of Al atoms and the effects of hydrating neighboring Al sites. These calculation were combined with {¹H}²⁷Al cross-polarization NMR experiments, carried out at high magnetic field (20 T) and high magic angle spinning (MAS) frequency (30 kHz) on γ-Al₂O₃ pretreated at different temperatures. We clearly show that this method is mainly sensitive to strongly hydrated surface sites besides the much more abundant bulk Al atoms, and that catalytically important high-<i>C</i>_Q Al centers (Lewis acid sites) and even some types of hydroxylated Al sites are not visible in the spectrum. Therefore, even current high-field NMR experiments are not (yet) able to provide a complete picture of the structure of γ-Al₂O₃ and much caution should be exercised when interpreting ²⁷Al NMR spectra