Catalytic Strategies for the Cycloaddition of Pure, Diluted, and Waste CO₂ to Epoxides under Ambient Conditions

Cyclic organic carbonates represent a relevant class of chemicals that can be prepared from CO₂ by cycloaddition to epoxides. The application of efficient catalysts is crucial in allowing the cycloaddition reaction to proceed under very mild conditions of temperature, pressure, and CO₂ concentration, thus resulting in a sustainable and carbon-balanced approach to CO₂ conversion. This is particularly the case if impure waste CO₂ could be employed as a feedstock. In this Review, we have critically analyzed the burgeoning literature on the cycloaddition of CO₂ to epoxides with the aim to provide state-of-the-art knowledge on the catalysts that can convert CO₂ to carbonates under ambient conditions. These have been systematically organized in families of compounds and critically scrutinized in terms of catalytic activity, availability and mechanistic features. Finally, we provide an overview on the catalytic systems able to function using diluted and impure CO₂ as a feedstock

Ascorbic Acid as a Bifunctional Hydrogen Bond Donor for the Synthesis of Cyclic Carbonates from CO₂ under Ambient Conditions

Readily available ascorbic acid was discovered as an environmentally benign hydrogen bond donor for the synthesis of cyclic organic carbonates from CO₂ and epoxides in the presence of nucleophilic cocatalysts. The ascorbic acid/TBAI (TBAI: tetrabutylammonium iodide) binary system could be applied for the cycloaddition of CO₂ to various epoxides under ambient or mild conditions. Density functional theory calculations and catalysis experiments revealed an intriguing bifunctional mechanism in the step of CO₂ insertion involving different hydroxyl moieties (enediol, ethyldiol) of the ascorbic acid scaffold

Exploring the Potential of Different-Sized Supported Subnanometer Pt Clusters as Catalysts for Wet Chemical Applications

The use of physicochemical preparation techniques of metal clusters in the ultrahigh vacuum (UHV) allows for high control of cluster nuclearity and size distribution for fundamental studies in catalysis. Surprisingly, the potential of these systems as catalysts for organic chemistry transformations in solution has not been explored. To this end, single Pt atoms and Pt clusters with two narrow size distributions were prepared in the UHV and applied for the hydrogenation of <i>p-</i>chloronitrobenzene to <i>p</i>-chloroaniline in ethanol. Following the observation of very high catalytic turnovers (approaching the million molecules of <i>p</i>-nitroaniline formed per Pt cluster) and of size-dependent activity, this work addresses fundamental questions with respect to the suitability of these systems as heterogeneous catalysts for the conversion of solution-phase reagents. For this purpose, we employ scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS) characterization before and after reaction to assess the stability of the clusters on the support and the question of heterogeneity versus homogeneity in the catalytic process

A Silica-Supported Monoalkylated Tungsten Dioxo Complex Catalyst for Olefin Metathesis

A well-defined silica-supported monoalkylated tungsten dioxo complex [(Si–O−)­W­(O)₂(CH₂–^<i>t</i>Bu)] was prepared by treatment of highly dehydroxylated silica (SiO_2‑700: silica treated at 700 °C under high vacuum) with an ionic precursor complex [NEt₄]­[W­(O)₃(CH₂–^<i>t</i>Bu)]. The identity of the resulting neutral monoalkylated tungsten dioxo surface complex was established by means of elemental microanalysis and spectroscopic studies (IR, solid-state NMR, Raman, and X-ray absorption spectroscopies). The supported tungsten complex was found to act as a precatalyst for the self-metathesis of 1-octene in a batch reactor. The mechanistic implications of this reaction are discussed with the support of DFT calculations highlighting the potential occurrence of thus-far unexplored mechanistic pathways

Heavy element production in a compact object merger observed by JWST

The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)1, sources of high-frequency gravitational waves (GW)2 and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process)3. Here we present observations of the exceptionally bright gamma-ray burst GRB 230307A. We show that GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers4–6, and contains a kilonova similar to AT2017gfo, associated with the gravitational-wave merger GW1708177–12. We obtained James Webb Space Telescope mid-infrared (mid-IR) imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass A=130), and a very red source, emitting most of its light in the mid-IR due to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the Universe.</p