Merging host-guest chemistry and organocatalysis for the chemical valorization of CO2

Cyclodextrin-Encapsulated NHCs: Increased Selectivity and Reactivity of CO2 in Amine Formylation

Herein, we describe the confinement of a N-Heterocyclic Carbene (NHC) organocatalyst in the cavity of cyclodextrins (CDs). These confined organocatalysts allow the formylation of amines through CO2 hydrosilylation. The presence of the cavity of the CDs leads to substrate-selectivity between amines in competition reactions. The use of the smallest α-CD induces the best selectivities but also increased reactivity compared to the bigger β-CD. A careful study conducted by NMR and DFT revealed that in α-CD, the complexed CO2 interacts with the cavity through hydrogen bonds. These H-bonds destabilize the NHC-CO2 adduct and are accountable for the higher reactivity observed using α-CD.

Recent Advances in the Chemical Fixation of Carbon Dioxide: A Green Route to Carbonylated Heterocycle Synthesis

Carbon dioxide produced by human activities is one of the main contributions responsible for the greenhouse effect, which is modifying the Earth’s climate. Therefore, post-combustion CO2 capture and its conversion into high value-added chemicals are integral parts of today’s green industry. On the other hand, carbon dioxide is a ubiquitous, cheap, abundant, non-toxic, non-flammable and renewable C1 source. Among CO2 usages, this review aims to summarize and discuss the advances in the reaction of CO2, in the synthesis of cyclic carbonates, carbamates, and ureas appeared in the literature since 2017.

Velcrand Functionalized Polyethylene

Velcrands are a specific class of cavitands whose complementary surfaces induce self-dimerization. The insertion of a velcrand as physical cross-linking unit into a polymer is reported. To this purpose, the velcrand was functionalized at the lower rim with an isocyanate group. The functional velcrand was reacted with poly (ethylene-co-(2-hydroxethylmethacrylate)) (PE-HEMA), a polymer equipped with free hydroxyl groups suitable for reaction with the isocyanate group. The obtained functionalized polymer was characterized by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR), proving the introduction of velcraplexes in the polymer. Films with varying amounts of velcrands were obtained by solution casting and slow evaporation, testifying the processability of the functionalized polymers. The obtained films were used to measure the oxygen barrier properties of the functionalized material.

Investigation of Hemicryptophane Host-Guest Binding Energies Using High-Pressure Collision-Induced Dissociation in Combination with RRKM Modeling

In advancing host-guest (H-G) chemistry, considerable effort has been spent to synthesize host molecules with specific and well-defined molecular recognition characteristics including selectivity and adjustable affinity. An important step in the process is the characterization of binding strengths of the H-G complexes that is typically performed in solution using NMR or fluorescence. Here, we present a mass spectrometry-based multimodal approach to obtain critical energies of dissociation for two hemicryptophane cages with three biologically relevant guest molecules. A combination of blackbody infrared radiative dissociation (BIRD) and high-pressure collision-induced dissociation (high-pressure CID), along with RRKM modeling, was employed for this purpose. For the two tested hemicryptophane hosts, the cage containing naphthyl linkages exhibited stronger interactions than the cage bearing phenyl linkages. For both cages, the order of guest stability is choline > acetylcholine > betaine. The information obtained by these types of mass spectrometric studies can provide new insight into the structural features that most influence the stability of H-G pairs, thereby providing guidance for future syntheses. Graphical Abstract.

Fluorinated Tetraphosphonate Cavitands

Two synthetic protocols for the introduction of fluorine atoms into resorcinarene-based cavitands, at the lower and upper rim, respectively, are reported. Cavitand 1, bearing four fluorocarbon tails, and cavitand 2, which presents a fluorine atom on the para position of a diester phosphonate phenyl substituent, were synthesized and their complexation abilities toward the model guest sarcosine methyl ester hydrochloride were evaluated via NMR titration experiments. The effect of complexation on the ¹⁹F NMR resonance of the probe is evident only in the case of cavitand 2, where the inset of the cation-dipole and H-bonding interactions between the P=O bridges and the guest is reflected in a sizable downfield shift of the fluorine probe.

A new heterogeneous host–guest catalytic system as an eco-friendly approach for the synthesis of cyclic carbonates from CO2 and epoxides

New host–guest catalytic systems were immobilized on silica supports and evaluated in the synthesis of cyclic carbonates from CO₂ and epoxides.

Amino-Functional Ionic Liquids as Efficient Catalysts for the Cycloaddition of Carbon Dioxide to Yield Cyclic Carbonates: Catalytic and Kinetic Investigation

Various amino-functional ionic liquids were developed as homogeneous catalysts for the cycloaddition of carbon dioxide to different epoxides yielding the corresponding cyclic carbonates under metal- and solvent-free conditions. The effects of reaction temperature, reaction time, CO2 pressure, and the amount of catalyst on the cycloaddition reaction were investigated. The catalysts could be easily recovered after the reaction and then reused at least eight times without noticeable loss of activity and selectivity. Reaction kinetic studies were undertaken, the reaction was apparently first order with respect to the concentration of epoxide and catalyst. Furthermore, the rate constants were determined over a temperature range of 100–130°C and the activation energy was determined to be 45.9 kJ mol−1. Finally, a possible reaction mechanism was proposed. The amino-functional ionic liquids showed the advantage of high catalytic activity and were easily recyclable for CO2 chemical fixation into valuable chemicals.

A tetrasulfate-resorcin[6]arene cavitand as the host for organic ammonium guests

A resorcin[6]arene cavitand bearing sulfate bridges is herein reported. The host is able to interact with ammonium guests through the sulfate bridges.