Revisiting the Potential of Group VI Inorganic Precatalysts for the Ethenolysis of Fatty Acids through a Mechanochemical Approach

The utilization of biobased feedstocks to prepare useful compounds is a pivotal trend in current chemical research. Among a varied portfolio of naturally available starting materials, fatty acids are abundant, versatile substrates with multiple applications. In this context, the ethenolysis of unsaturated fatty acid esters such as methyl oleate is an atom-economical way to prepare functional C10 olefins with a biobased footprint. Despite the existence of a variety of metathesis catalysts for the latter process, there is a lack of readily available, efficient, and inexpensive catalytic systems based on earth-abundant metals (Mo, W) whose preparation does not require sophisticated syntheses and manipulations. Here, a systematic exploration of homogeneous and heterogeneous inorganic Mo, W (oxy)halides shows that MoOCl4, while inactive as a homogeneous species, forms active and selective silica-supported ethenolysis precatalysts able to reach equilibrium conversion of methyl oleate within a few minutes upon activation with SnMe4. Such heterogeneous MoOCl4-based precatalysts were easily accessed through mechanochemical solvent-free procedures and found to contain, upon characterization by elemental analysis and Raman spectroscopy, isolated (≡SiO)Mo(=O)Cl3 units or polymeric silica-supported [-O(≡SiO)nMoCl4-nO-]m (n = 1, 2) complexes depending on the molybdenum loading. The former isolated species exhibited a higher catalytic performance. The developed heterogeneous precatalysts could be applied to the ethenolysis of various substrates, including polyunsaturated fatty acid esters and industrial fatty acid methyl ester (FAME) mixtures from palm oil transesterification.

Samarium- and Ytterbium-Grafted Periodic Mesoporous Silica for Carbon Dioxide Capture and Conversion

Immobilized coordination compounds of Lewis acidic metals are powerful catalytic components of systems for the cycloaddition of CO2 to epoxides that do not require sophisticated coordination frameworks to harness the metal center and modulate its activity. Surface organometallic chemistry (SOMC) is a valuable methodology to prepare well-defined and site-isolated surface complexes and coordination compounds on metal oxides, with ligand environments easily adjustable to a targeted catalytic reaction. In this work, the SOMC methodology is applied to prepare SmII, YbII, and SmIII alkoxide surface complexes on periodic mesoporous (organo)silica of distinct pore symmetry/size for application in the CO2 cycloaddition reaction. The surface complexes are readily accessible by the grafting of the bis(trimethylsilyl)amide precursors LnII[N(SiMe3)2]2(THF)2 (Ln = Sm, Yb) and SmIII[N(SiMe3)2]3, followed by ligand exchange with alcohols (ethanol and neopentanol). The use of periodic mesoporous supports led to hybrid materials with relatively high surface areas and pore sizes, affording good performance in CO2 capture and in the cycloaddition of CO2 to epoxides under mild conditions (60-80 °C, 1-10 bar). In terms of catalytic performance, recyclability, and low amount of added nucleophile TBAX (X = Br, I), the most active materials prepared in this work compare well to a variety of previously reported SOMC-derived surface complexes and to other heterogeneous Lewis acids displaying more elaborate ligand environments.

Green Energy by Hydrogen Production from Water Splitting, Water Oxidation Catalysis and Acceptorless Dehydrogenative Coupling

In this review, we want to explain how the burning of fossil fuels is pushing us towards green energy. Actually, for a long time, we have believed that everything is profitable, that resources are unlimited and there are no consequences. However, the reality is often disappointing. The use of non-renewable resources, the excessive waste production and the abandonment of the task of recycling has created a fragile thread that, once broken, may never restore itself. Metaphors aside, we are talking about our planet, the Earth, and its unique ability to host life, including ourselves. Our world has its balance; when the wind erodes a mountain, a beach appears, or when a fire devastates an area, eventually new life emerges from the ashes. However, humans have been distorting this balance for decades. Our evolving way of living has increased the number of resources that each person consumes, whether food, shelter, or energy; we have overworked everything to exhaustion. Scientists worldwide have already said actively and passively that we are facing one of the biggest problems ever: climate change. This is unsustainable and we must try to revert it, or, if we are too late, slow it down as much as possible. To make this happen, there are many possible methods. In this review, we investigate catalysts for using water as an energy source, or, instead of water, alcohols. On the other hand, the recycling of gases such as CO2 and N2O is also addressed, but we also observe non-catalytic means of generating energy through solar cell production.

Carbon Dioxide Conversion on Supported Metal Nanoparticles: A Brief Review

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

Alumina-Based Bifunctional Catalyst for Efficient CO2 Fixation into Epoxides at Atmospheric Pressure

The quest toward sustainability and decarbonization demands the development of methods for efficient carbon dioxide capture and utilization. The nonreductive CO₂ fixation into epoxides to prepare cyclic carbonates has gained attention in recent years. In this work, we report the development of guanidine hydrochloride-functionalized γ alumina (γ-Al₂O₃), prepared using green solvents, as an efficient bifunctional catalyst for CO₂ fixation. The resulting guanidine-grafted γ-Al₂O₃ (Al-Gh) proved to be an excellent catalyst to prepare cyclic carbonates from epoxides and CO₂ with high selectivity. The nitrogen-rich Al-Gh shows increased CO₂ adsorption capacity compared to that of γ-Al₂O₃. The as-prepared catalyst was able to carry out CO₂ fixation at 85 °C under atmospheric pressure in the absence of solvents and external additives (e.g., TBAI or KI). The material showed negligible loss of catalytic activity even after five cycles of catalysis. The catalyst successfully converted many epoxides into their respective cyclic carbonates under the optimized conditions. The gram-scale synthesis of commercially important styrene carbonates from styrene oxide and CO₂ using Al-Gh was also achieved. Density functional theory (DFT) calculations revealed the role of alumina in activating the epoxide. This activation facilitated the chloride ion to open the ring to react with CO₂. The DFT studies also validated the role of alumina in stabilizing the electron-rich intermediates during the course of the reaction.

Tabrizi B, D’Elia V, Del Gobbo S, Jabbour GE. Microwave-Assisted Non-aqueous and Low-Temperature Synthesis of Titania and Niobium-Doped Titania Nanocrystals and Their Application in Halide Perovskite Solar Cells as Electron Transport Layers

Undoped and Nb-doped TiO₂ nanocrystals are prepared by a microwave-assisted non-aqueous sol-gel method based on a slow alkyl chloride elimination reaction between metal chlorides and benzyl alcohol. Sub-4 nm nanoparticles are grown under microwave irradiation at 80 °C in only 3 h with precise control of growth parameters and yield. The obtained nanocrystals could be conveniently used to cast compact TiO₂ or Nb-doped TiO₂ electron transport layers for application in formamidinium lead iodide-based photovoltaic devices. Niobium doping is found to improve the cell performance by increasing the conductivity and mobility of the electron transport layer. At the same time, a measurable decrease in parasitic light absorption in the low wavelength portion of the spectrum was observed.

Catalytic Performance and Electrophoretic Behavior of an Yttrium-Organic Framework Based on a Tricarboxylic Asymmetric Alkyne

A new Y-based metal-organic framework (MOF) GR-MOF-6 with a chemical formula of {[YL(DMF)₂]·(DMF)}_n {H₃L = 5-[(4-carboxyphenyl)ethynyl] isophthalic acid; DMF = N,N-dimethylformamide} has been prepared by a solvothermal route. Structural characterization reveals that this novel material is a three-dimensional MOF in which the coordination of the tritopic ligand to Y(III) metal ions leads to an intercrossing channel system extending over three dimensions. This material has proven to be a very efficient catalyst in the cyanosilylation of carbonyls, ranking second in catalytic activity among the reported rare earth metal-based MOFs described so far but with the lowest required catalyst loading. In addition, its electrophoretic behavior has been studied in depth, providing a zero-charge point between pH 4 and 5, a peak electrophoretic mobility of -1.553 μm cm V^-1 s^-1, and a ζ potential of -19.8 mV at pH 10.

Dataset for the synthesis and application of single-component heterogeneous catalysts based on zinc and tin for the cycloaddition of pure, diluted, and impure CO2 to epoxides under mild conditions

The cycloaddition of CO₂ to epoxides under mild conditions is a growing field of research and a viable strategy to recycle CO₂ in the form of cyclic carbonates as useful intermediates, solvents, and additives. This target requires readily accessible and recyclable catalysts whose synthesis does not involve expensive monomers, multistep procedures, coupling reagents, etc. Additionally, the catalysts should be active under atmospheric pressure and tolerate impurities such as methane and H₂S. In a recent manuscript (Rational engineering of single-component heterogeneous catalysts based on abundant metal centers for the mild conversion of pure and impure CO₂ to cyclic carbonates;Chemical Engineering Journal 422 (2021) 129930) we have developed strategies to prepare efficient heterogeneous catalysts for the cycloaddition reaction of CO₂ to epoxides. Such materials consist of dispersions of metal halides (ZnCl₂ or SnCl₄) on silica support that is further functionalized with ionic liquids bearing nucleophilic halide moieties for cooperative epoxide activation and ring-opening. Herein, we provide useful complementary data for the characterization of the prepared materials in the form of: SEM images of materials (SEM: scanning electron microscope), SEM-EDS images of materials (EDS: Energy-dispersive X-ray spectroscopy), TEM images of materials (TEM: transmission electron microscope); XPS (X-ray photoelectron spectroscopy) survey spectra of most active catalysts and related high-resolution spectra in spectral regions of interest, BET (Brunauer–Emmett–Teller) physisorption isotherms of materials, raw ¹H NMR spectra of catalytic reactions to verify the reproducibility of the reaction outcome and identify the reaction products.

Fixation of atmospheric CO2 as C1-feedstock by nickel(ii) complexes

The development of molecular catalysts for the activation and conversion of atmospheric carbon dioxide (CO₂) into a value-added product is a great challenge. A series of nickel(ii) complexes, [Ni(L)(CH₃CN)₃](BPh₄)₂, 1-4 of diazepane based ligands, 4-methyl-1-[(pyridin-2-yl-methyl)]-1,4-diazepane (L1), 4-methyl-1-[2-(pyridine-2-yl)ethyl]-1,4-diazepane (L2), 4-methyl-1-[(quinoline-2-yl)-methyl]-1,4-diazepane (L3) and 1-[(4-methoxy-3,5-dimethyl-pyridin-2-yl)methyl]-4-methyl-1,4-diazepane (L4), have been synthesized and characterized as catalysts for the activation of atmospheric CO₂. The single-crystal X-ray structure of 1 shows a distorted octahedral geometry with a cis-β configuration around the NiN₆ coordination sphere. All the complexes are used as catalysts for the conversion of atmospheric CO₂ and epoxides into cyclic carbonates at 1 atmosphere (atm) pressure and in the presence of Et₃N. Catalyst 4 was found to be the most efficient catalyst and showed a 31% formation of cyclic carbonates with a TON of 620 under 1 atm air as the CO₂ source. This yield was enhanced to 94% with a TON of 1880 under 1 atm pure CO₂ gas and it is the highest catalytic efficiency known for nickel(ii)-based catalysts. Catalyst 4 enabled the transformation of a wide range of epoxides (eight examples) into corresponding cyclic carbonates with excellent selectivity (>99%) and yields of 59-94% and 11-31% under pure CO₂ and atmospheric CO₂, respectively. The catalytic efficiency is strongly influenced by the electronic nature of the complexes. The CO₂ fixation reactions without an epoxide substrate led to the formation of the carbonate bridged dinuclear nickel(ii) complexes [(LNi^II)₂CO₃](BPh₄)₂1a-4a, which are speculated as catalytically active intermediates. The formation of these species was accompanied by the formation of new absorption bands around 592-681 nm and was further confirmed by the ESI-MS and IR spectral studies. The molecular structures of these carbonate-bridged key intermediates were determined by X-ray analysis. The structures contain two Ni²⁺-centers bridged via a carbonate ion that originated from CO₂. Distorted square pyramidal geometries are adopted around each Ni(ii) center. All these results support that CO₂ fixation reactions occur via CO₂-bound nickel key intermediates.

Pressure-induced electrides and metallic phases in the Y-Cl system

Pressure can profoundly change the electronic structure, leading to the formation of new phases and materials with exotic properties. Herein, using evolutionary algorithms and density functional theory, we systematically investigate the behaviour of materials in the yttrium-chlorine binary system under pressure. Electrons are found to be spatially confined at low pressures in yttrium chlorides and tend to form new electrides. In particular, a novel yttrium chloride, Y₃Cl₂, is predicted to be thermodynamically and lattice dynamically stable at approximately 10 GPa. Further analyses of the electron localization function and partial charge density identify trigonal Y₃Cl₂as a new 2D high-pressure electride with partially localized electrons contributing to the conduction. By further increasing the pressure, electrons in the yttrium-chlorine binary system tend to delocalize with the electrides decomposing into two new compounds (Y₂Cl and YCl₂) and a new YCl phase (space groupP6₃/mmc) above 20 GPa. These newly discovered phases are all metallic in their stable pressure range according to band structure simulations without interstitial electron localization. The discovery of these unconventional yttrium chlorides may inspire strategies to search for low-pressure electrides in other rare-earth halogenide systems.

Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation

Homoleptic ceric pyrazolates (pz) Ce(RR’pz)₄ (R = R’ = tBu; R = R’ = Ph; R = tBu, R’ = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe₂)₂]₄ with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO₂, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO₂ insertion was found to increase in the order of tBu₂pz < Ph₂pz < tBuMepz < Me₂pz. For comparison, the pyrrole-based ate complexes [Ce₂(pyr)₆(µ-pyr)₂(thf)₂][Li(thf)₄]₂ (pyr = pyrrolato) and [Ce(cbz)₄(thf)₂][Li(thf)₄] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe₂)₂]₄Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO₂ seemed promising, but any reversibility could not be observed.

Heterobimetallic rare earth metal-zinc catalysts for reactions of epoxides and CO2 under ambient conditions

Four homodinuclear rare earth metal (RE) complexes 1-4 bearing a multidentate diglycolamine-bridged bis(phenolate) ligand were synthesized. In addition, seven heterobimetallic RE-Zn complexes 5-11 were prepared through a one-pot strategy. In these heterobimetallic complexes, two RE centers are bridged by either Zn(OAc)₂ or Zn(OBn)₂ moieties. All complexes were characterized by single crystal X-ray diffraction, elemental analysis, IR spectroscopy, and multinuclear NMR spectroscopy (in the case of diamagnetic complexes 1, 4, 7 and 11). Moreover, the multi-nuclear structures of complexes 4 and 11 in solution were also studied by ¹H DOSY spectroscopy. These complexes were applied in catalyzing the coupling reaction of carbon dioxide (CO₂) with epoxides. Zn(OAc)₂- and Zn(OBn)₂-bridged heterobimetallic complexes showed comparable catalytic activities under ambient conditions and were more active than monometallic RE complexes. Significant synergistic effect in heterobimetallic complexes is observed. Mono-substituted epoxides were converted into cyclic carbonates under 1 atm CO₂ at 25 °C in 88-96% yields, whereas di-substituted epoxides reacted under 1 atm CO₂ at higher temperatures in 40-80% yields.

Cycloaddition of CO2 to epoxides by highly nucleophilic 4-aminopyridines: establishing a relationship between carbon basicity and catalytic performance by experimental and DFT investigations

New highly nucleophilic homogeneous and heterogeneous catalysts based on the 3,4-diaminopyridine scaffold are reported for the halogen-free cycloaddition of CO₂ to epoxides.

Crosslinked porous polyimides: structure, properties and applications

Porous polyimides (pPIs) represent a fascinating class of porous organic polymers (POPs). Here the properties and functions of amorphous and crystalline pPIs are reviewed, and applications contributing to solutions to global challenges highlighted.

Cerium Pyrazolates Grafted onto Mesoporous Silica SBA-15: Reversible CO2 Uptake and Catalytic Cycloaddition of Epoxides and Carbon Dioxide

The activation and catalytic conversion of CO₂ is a current topic relating to molecular chemistry and materials science alike. As a transdisciplinary field of research, surface organometallic chemistry (SOMC) might be applicable to perform synergistically, thus striking a new path in sustainable chemistry. Both ceric and cerous rare-earth-metal pyrazolates, which were recently shown to reversibly insert CO₂ and to promote the catalytic cycloaddition of epoxides and carbon dioxide, were grafted onto large-pore mesoporous silica SBA-15₅₀₀, thermally pretreated at 500 °C. The obtained hybrid materials [Ce(Me₂pz)₄]₂@SBA-15₅₀₀, Ce(Me₂pz)₄(thf)@SBA-15₅₀₀, Ce₄(Me₂pz)₁₂@SBA-15₅₀₀, and [Ce(Me₂pz)₃(thf)]₂@SBA-15₅₀₀ (Me₂pz = 3,5-dimethylpyrazolato) were characterized by DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy), solid-state ¹H/¹³C NMR spectroscopy, elemental analysis, ICP/OES, and N₂ physisorption. The lanthanum(III)-based material [La(Me₂pz)₃(thf)]₂@SBA-15₅₀₀ was synthesized for better assessment of the cerous materials being highly sensitive to oxidation. To mimic ceric surface species, Ce[OSi(OtBu)₃]₃Cl was treated with 1 equiv of K(Me₂pz), generating the mixed pyrazolyl/siloxy complex KCe[OSi(OtBu)₃]₄(Me₂pz) featuring a cerium(IV)-bonded terminal pyrazolato ligand. All hybrid materials show efficient and reversible carbon dioxide uptake of maximum 20 wt % in the solid state. When combined with tetra-n-butylammonium bromide (TBAB), the hybrid materials catalyze the cycloaddition of CO₂ and epoxides, displaying good conversion of various epoxides and reusability.

Intertwined chemistry of hydroxyl hydrogen-bond donors, epoxides and isocyanates in the organocatalytic synthesis of oxazolidinones versus isocyanurates: rational catalytic investigation and mechanistic understanding

The efficiency and chemoselectivity of the cycloaddition of isocyanates to epoxides to afford oxazolidinones were investigated using hydroxyl hydrogen-bond donors as organocatalysts.

B-Doped and NH2-functionalized SBA-15 with hydrogen bond donor groups for effective catalysis of CO2 cycloaddition to epoxides

The novel B-SBA-15-NH₂ catalyst with Lewis acid–base properties and hydrogen bond donor groups exhibited good catalytic performance for CO₂ conversion under metal- and solvent-free conditions.

Dual hydrogen-bond donor group-containing Zn-MOF for the highly effective coupling of CO2 and epoxides under mild and solvent-free conditions

A novel 3D Zn₃(L)₃(H₂L) MOF with dual hydrogen-bond donor (HBD) groups exhibited an efficient catalytic performance for the CO₂ cycloaddition with epoxides under 80 °C, 1.0 MPa and solvent-free conditions.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C-C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(ii) and Ln(iii) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(iii) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion.

Gold incorporated hematite nanocatalyst for solvent-free CO2 fixation under atmospheric pressure

Au/α-Fe₂O₃ as a nanocatalyst for the conversion of epoxides to cyclic carbonates utilizing CO₂ under 1 atm. pressure.