Rearrangement, Nucleophilic Substitution, and Halogen Switch Reactions of Alkyl Halides over NaY Zeolite: Formation of the Bicyclobutonium Cation Inside the Zeolite Cavity

Zeolites as Solid Solvents: Explaining the Chloromethane Hydrolysis over Metal-Exchanged Zeolite Y by DFT Calculations

We report a theoretical DFT study of the reaction pathways for chloromethane hydrolysis over metal-exchanged zeolites (Li+, Na+, K+, and Mg2+). A cluster of 78 T atoms (T referring to Si or Al atoms), comprising the zeolite Y super cavity coupled with the sodalite cage and three hexagonal prism units (Si(78-x)Al x O129H54; x = 1 or 2), was used in the calculations. The study was carried out using the ONIOM method. The high layer was computed at M062X/6-31++G(d,p), whereas the low layer was computed at the PM6 level of theory. The energy profile was obtained by single-point calculations at the M062X/6-31++G(d,p) for the entire structure. The first step studied was the adsorption of chloromethane on the zeolite, which involves an ion-dipole interaction between the metal cation and the chlorine atom. Then, two mechanistic pathways were investigated: one via formation of an adsorbed methoxide and the other involving a direct, one-step, nucleophilic attack of the water molecule to the adsorbed chloromethane. In all systems studied, the direct mechanism showed a lower energy of activation than the route involving the methoxide intermediate. The same behavior was also observed for chloromethane methanolysis to afford dimethyl ether on the metal-exchanged zeolites. The theoretical results are in agreement with the experiments of chloromethane hydrolysis over metal-exchanged zeolite Y, explaining the formation of dimethyl ether upon chloromethane methanolysis on zeolites of low or no acidity. The transition state for the direct route resembles a SN2 process assisted by the surface, reinforcing the concept of zeolites as solid solvents, providing a polar nanoenvironment that favors and assists the formation of ionic transition states and intermediates.

Rapid Access to Arylated and Allylated Cyclopropanes via Brønsted Acid-Catalyzed Dehydrative Coupling of Cyclopropylcarbinols

A regioselective protocol for the synthesis of cyclopropyl derivatives that relies on Brookhart acid-catalyzed dehydrative coupling over substituted cyclopropylcarbinols without rearrangement is reported herein. The reactions proceed promptly at 25 °C with only 2.0 mol % catalyst loading and produce the cyclopropyl derivatives in excellent yields. This method is well tolerated with a vast range of cyclopropylcarbinols including aliphatic cyclopropylcarbinols, where no elimination product was obtained, demonstrating the protocol's utility. Further, the Hammett correlation suggested the formation of a cyclopropylcarbinyl cation followed by a coupling reaction. An extremely effective gram-scale reaction has also been demonstrated with a high turnover number.

Zeolite-mediated production of cyclic organic carbonates: reaction of CO2 with styrene oxide on zeolite Y impregnated with metal halides

Zeolites impregnated with metal halides as efficient catalysts for cyclic organic carbonate production.

Intramolecular cyclopropylmethylation via non-classical carbocations

Cyclopropyl-cyclopropyl rearrangement can be achieved selectively by intramolecular trapping of cyclopropylmethyl carbenium ions with an internal nucleophile. This can be exploited as a useful method for the introduction of a cyclopropyl group into complex molecules using readily accessible disubstituted cyclopropane intermediates.

Solid solvents: activation parameters for the rearrangement of cyclopropylcarbinyl bromide on mordenite zeolite

Rearrangement of cyclopropylcarbinyl bromide over proton and ammonium-exchanged mordenite (H-MOR and NH₄-MOR) was studied at different temperatures.