Understanding into interfacial properties and reactivity of COFs toward accelerating Menshutkin SN2 reaction

Given the poor understanding about the effects of confined polar microenvironment on interfacial behaviors of Menshutkin SN2 reaction, herein, the interfacial properties and reactivities between 1-methylimidazole and methyl thiocyanate reaction induced by interfacial polar microenvironments of covalent organic frameworks (COFs) with varying pore size and functional groups were investigated using in situ Fourier transform infrared spectroscopy, molecular dynamics simulations, and metadynamics calculations. The decreased nanopore size of COFs from 3.2 to 1.2 nm can enlarge reaction rates (k) and reduce activation energy barriers (ΔE*). The hydroxyl-modified COF (2.8 nm) can further cause larger k and lower ΔE* by 6.1 and 0.8 kJ/mol compared to the bulk and smaller pore-size COF (1.2 nm) system, respectively, mainly originating from induced higher aggregation, preferred orientation, and the stabilization of charge separation of transition state. This work provides a systematic understanding for the confined interfacial properties toward accelerating the Menshutkin reaction.