Atom Transfer Radical Polymerization (ATRP) is one breakthrough technique to obtain well-defined and controlled polymers or copolymers. However, this technique has been mainly considered in solution and alternatives such as solvent-free mechanochemistry in a ball-mill, an emerging approach for a greener and safer chemistry, is left aside as a tool for polymer synthesis. Nevertheless, mechanochemistry in a ball-mill offers many advantages and permits to avoid the use of solvent, with shorter reaction times and simplified treatment steps making it easier to recover the product of interest. Herein, interest was put onto the development of mechanochemical ARGET-ATRP conditions for styrene polymerization, one solid styrenic derivative sodium styrene sulfonate, one liquid styrenic derivative 4-vinylbenzyl chloride and a mixture of both monomers. A fine tuning of the catalyst quantity and easily removable ascorbic acid/Na2CO3 reducing agent, never describe in the ball-mill previously and more practical than other reducing agent, gave polymers and copolymers in good to excellent yield (up to >99 %), with a control over dispersity (typically Đ < 1.5), as analyzed by 1H NMR and size exclusion chromatography, respectively. As a further matter, these unprecedented conditions allow to render null and void all considerations concerning the physical state, properties (hydrophilic, hydrophobic) and miscibility/solubility of monomers which are key parameters in solution based ATRP for the synthesis of polymer and copolymer.
This review describes the thermodynamics of C-H bond activation in various hydrocarbons, especially (poly)fluorinated benzenes, by transition metal complexes, through experiments and computational studies, with a focus on the latter. Experimental metal-carbon bond dissociation enthalpies (BDEs), determined relative to an internal reference, were used to establish the relationship between H-C and M-C BDEs. In parallel, bond dissociation enthalpies or energies were computed with DFT methods. For a given metal complex and a set of sufficiently similar organic substrates a linear correlation with a characteristic slope R M-C/H-C was obtained. Both experimental and computational studies indicate that the slope is always greater than 1 and quantitatively agree on its value when comparison could be made, suggesting a systematic thermodynamic preference for cleaving stronger hydrogen-carbon bonds. The R M-C/H-C value is particularly high for (poly)fluorobenzenes, with the greatest increase in M-C BDE occurring when fluorine atoms are ortho to the M-C bond, as found by experiments. The polarity
Boroaluminates are mixed oxides of boria and alumina that show promise for various catalytic applications due to their mild acidity. In this work, boroaluminate xerogels were successfully synthesized via alternative non-hydrolytic sol-gel (NHSG) ether elimination pathways, offering a controlled, template-free strategy for their design. We investigated the synthesis using four distinct alkoxide precursor combinations, utilizing aluminum isopropoxide and sec-butoxide as aluminum sources, alongside boron methoxide and isopropoxide as boron sources. This ether elimination approach provides an excellent alternative to traditional alkyl halide elimination routes, allowing the final porosity, coordination states, and surface acidity to be targeted more easily solely through precursor selection and precursor-to-solvent ratios. The synthesized boroaluminates exhibit a highly homogeneous bulk dispersion of aluminum and boron throughout the xerogel networks (as confirmed by XPS, ICP-OES, and EDS mapping), though calcination at 600 °C led to a surface depletion of boron species. Three of the four synthetic pathways yielded high-surface-area materials (590–772 m2 g–1) without the use of structure-directing agents. Analysis by 11B and 27Al MAS NMR, combined with NH3-TPD revealed that precursor choice directly affects the local atomic coordination, yielding unique catalytic centers—specifically 5-coordinated aluminum alongside 3- and 4-coordinated boron—and a heterogeneous distribution of weak and medium acid sites. Additionally, these materials were evaluated as heterogeneous catalysts in the dehydration of ethanol. The boroaluminates exhibited highly temperature-dependent selectivity, favoring diethyl ether at lower temperatures and shifting predominantly to ethylene at higher temperatures. Four of the five prepared samples showed promising catalytic activity, consistently achieving ethanol conversions between 79 % and 93 % at 275 °C.
With the rapid increase in temperatures around the planet, the need to develop efficient means to reduce CO2 emissions has become one of the greatest challenges of the scientific community. Many different strategies are being studied worldwide, one of which consists of trapping the gas in porous materials, either for its short- or long-term capture and storage, or its re-use for the production of value-added compounds. Yet, to further the development of such systems, there is a real need to fully understand their structure and properties, including at the molecular-level following the physisorption and/or chemisorption of CO2 (which can lead to various species, including carbonate and bicarbonate ions). In this context, 17O NMR naturally appears as the analytical tool of choice, because of its exquisite sensitivity to probe subtle differences in oxygen bonding environments. To date, it has scarcely been used, due to the very low natural abundance of 17O (0.04%), and the difficulty in purchasing or obtaining commercial 17O-labeled compounds adapted to such investigations (e.g., 17O-CO2(g), or 17O-enriched Na- and K-(bi)carbonate salts, which can be readily transformed into CO2). Herein, we demonstrate how, using mechanochemistry, it is possible to enrich with 17O a variety of Na- and K-(bi)carbonate salts in a fast, economical, scalable, and user-friendly way. The high enrichment levels enabled recording the first high-resolution 17O ssNMR spectra of these phases at different temperatures and magnetic fields. From these, the typical spectral signatures of (bi)carbonate ions could be obtained, showing their strong sensitivity to local environments and dynamics. Lastly, we show how thanks to the selective 17O-labeling, other aspects of the reactivity of carbonates in materials can be unveiled using in situ 17O ssNMR. In the long run, it is expected that this work will open the way to more profound investigations of the structure and properties of carbon capture and storage systems, and, more generally speaking, of functional materials containing carbonates.
