Mechanism for CO₂ Fixation with Aziridines Synergistically Catalyzed by HKUST-1 and TBAB: A DFT Study

Abstract

It was revealed in recent experimental studies that metal–organic frameworks (MOFs) show very attractive activities for the catalytic CO2 cycloaddition with aziridines in cooperation with tetrabutylammonium bromide (TBAB). However, the mechanistic details and the selectivity origin remain largely uncertain, rendering great difficulty for a logical improvement of the existing catalysts and the rational design of new catalysts. In this work, the HKUST-1/TBAB-catalyzed CO2–aziridine cycloaddition reaction mechanism was comparatively explored with the noncatalyzed and HKUST-1-catalyzed cases at the density functional theory (DFT) level. Our calculations showed that the HKUST-1/TBAB-catalyzed cycloaddition proceeds through a three-step mechanism involving the ring opening of aziridine, CO2 insertion, and intramolecular cyclization. Additionally, CO2 cycloaddition is much easier for the HKUST-1/TBAB catalytic systems (26.1 kcal mol–1) than for the noncatalytic (44.3 kcal mol–1) and HKUST-1-catalytic (33.6 kcal mol–1) systems. The preferential cleavage of the substituted over the unsubstituted C–N bond of aziridine in the step of ring opening is the origin of the preferential formation of 5-substituted oxazolidinone as observed in experiment. Additionally, the energy barriers for the steps of ring opening and ring closure depend greatly on the nucleophilicity of the cocatalysts. Tetrabutylammonium chloride (TBAF) and tetrabutylammonium chloride (TBAC) were predicted to be efficient cocatalysts that can overcome the existing TBAB used in experimental reports. The proton attachment energy (PAE) of the halogen anion is correlated as the function of the energy barrier for the key steps. The in silico investigations should pave the way for designing more powerful catalytic materials for the chemical conversion of CO2 by aziridine.

Recyclable and Magnetically Functionalized Metal–Organic Framework Catalyst: IL/Fe3O4@HKUST-1 for the Cycloaddition Reaction of CO2 with Epoxides

“…Based on the experimental observations that the presence of both HKUST-1 and IL is required for effective catalysis, ,− a plausible cycloaddition reaction mechanism catalyzed by the IL/Fe 3 O 4 @HKUST-1 involving the consecutive insertion of carbon dioxide, ring-opening of epoxide, and ring closure of cyclic carbonate is presented in Scheme . Initially, the positively charged ammonium ion acts as a Lewis acid to polarize and activate the C–O bond in CO 2 , followed by the nucleophilic addition of the BF 4 – group to the carbon atom of carbon dioxide.…”

Non-Noble-Metal Metal–Organic-Framework-Catalyzed Carboxylative Cyclization of Propargylic Amines with Atmospheric Carbon Dioxide under Ambient Conditions

“…Thus, the Cu 2 I 2 cluster was employed as the model for calculating the MOF-based catalytic mechanism. Considering the constraints imposed by the rigid framework, only the Cu atom as the catalytically active center was allowed to relax and the remaining atoms in the framework were kept fixed during geometry optimization, which is consistent with previous MOF-based calculations. , The self-consistent reaction field based on the polarized continuum model was employed for considering the solvent effect of acetonitrile (CH 3 CN). Intrinsic reaction coordinate calculations were carried out to confirm that the transition state precisely connects the desired consecutive minima .…”

A more effective catalysis of the CO2 fixation with aziridines: computational screening of metal-substituted HKUST-1

“…According to a large number of literature reports, for the metal-organic framework taken as an catalyst, its framework usually plays a supporting and auxiliary role, whereas the unsaturated metal sites play catalytic roles, namely Lewis acid sites. [36,39,[64][65][66][67]In the beginning, the catalytic reaction is initiated when Ti, Mn, Zn, Fe and Zr) .…”

“…Alternatively, thanks tovarious attractive features of metal−organic frameworks (MOFs) such as the designable structures,adjustable functional groups, well-defined pores, high surfacearea, significant capability for gas-adsorption, and excellentrecyclable catalytic performance [25][26][27][28][29][30], chemists have very recently turned to explore the possibility of various MOF-based catalysts for the cycloaddition of CO 2 with aziridines [31][32][33][34][35][36].These laboratory studies have shown that as an efficient and heterogeneous catalyst, structurally diversified MOFsincluding [ [32]canbe regarded as the optimal candidates for the catalytic reaction of CO 2 with aziridines. Although the pursuit of novel, structurally diversified and high catalytic reactivity catalysts is a never-ending task, the frequently encountered synthetic challenge as well as the difficulty for unraveling the reaction mechanism in laboratory have greatly hindered the advancement of the catalytic chemistry of CO 2 with aziridines by MOFs.…”

“…Although the pursuit of novel, structurally diversified and high catalytic reactivity catalysts is a never-ending task, the frequently encountered synthetic challenge as well as the difficulty for unraveling the reaction mechanism in laboratory have greatly hindered the advancement of the catalytic chemistry of CO 2 with aziridines by MOFs. In fact, the reported examples for MOF-catalyzed CO 2 cycloaddition with aziridines have been very limited [31][32][33][34][35][36].Luckily, quantum chemical computational techniques have now evolved into a very powerful tool to tackle the above problems. [37,38] The detailed mechanistic study could help deduce the key factors for an effective reaction pathway, with which we can screen out possible catalyst candidates from a number of experimentally untouched reactions.…”