CO₂ Sequestration by Triazolylidene-Derived N-Heterocyclic Olefins: A Computational Study

Abstract

In the current work, computational modeling was used to explore the potential of 1,2,4-triazolylidene-derived N-heterocyclic olefins (trNHOs) systems as CO 2 capturer. After new structural modifications are performed, the energy required to activate CO 2 by m-trNHOs systems is lower than that observed in known analogous systems. Further substitutions were carried out in the triazolium ring showing that faster CO 2 sequestration or more suitable carboxylate for CO 2 storage can be favored depending on the selected substituent group. In addition, the nucleophilicity index, the molecular electrostatic potential (MESP) and the Density Overlap Regions Indicator (DORI) analysis were used to shed more light on their reactivity, stability and electronic structure.

The Brönsted Basicities of N-Heterocyclic Olefins in DMSO: An Effective Way to Evaluate the Stability of NHO–CO2 Adducts

“…Although there have been sporadic reports on the basicities for several imidazoline- and thiazole-derived NHOs in solution, and very recently, the proton affinities (PA) of 19 NHOs in the gas phase were calculated, to the best of our knowledge, so far there is no systematic research into the basicities of a broad range of NHOs in solution. Therefore, in the present work, first, the basicities of some commonly used NHOs (Figure ) were investigated using a well-established theoretical method for p K a calculations in solution, that is, SMD/M06-2x/6–311++G­(2df,2p)//B3LYP-D3/6–31+G­(d), which has been applied to the acidity predictions for a wide spectrum of Brönsted acids in DMSO, including thiols, chiral phosphoric acids, carboxylic acids, imides, and carbon acids, with fairly small mean unassigned errors (MUEs). , Since the activation and catalytic transformation of thermodynamically stable CO 2 are currently one of the major applications of NHOs, it is sensible to establish a practical way to evaluate the stability of NHO–CO 2 adducts . In light of this, we then calculated the Gibbs energies for the formation of NHO–CO 2 adducts (Δ G r ) in DMSO, whereby a linear free energy relationship (LFER) was established in order to provide an insight into the underlying relationship between the basicity of NHOs and stability of NHO–CO 2 adducts on the basis of thermodynamics.…”

“…In recent years, the chemical community has witnessed versatile utilities of NHOs in modern organic syntheses. In this regard, NHOs have found their broad applications in CO 2 sequestration and transformation, polymerization, , main group chemistry, and metal-mediated catalysis …”

Proton Affinities of N-Heterocyclic Olefins and Their Implications for Organocatalyst Design

“…This electronic situation renders NHOs capable Brønsted bases and strong nucleophiles, which in turn makes them interesting candidates as catalytically active components in a broad range of chemical transformations. In view of these characteristics, NHOs are increasingly employed as organocatalysts, including for example CO 2 sequestration, − base-catalyzed alkylations, silylation reactions, hydroborylations, ring-opening polymerization of epoxides , or lactones, and the zwitterionic polymerization of acrylates . In combination with Lewis acids, NHOs have also performed competently as co-catalysts for polymerizations reactions, enabling novel selectivities and the conversion of challenging monomers. − Further fields of application include the stabilization of unusual oxidation sates or of sensitive compounds , and also generally the employment of NHOs as ligands .…”

The Lewis Pair Polymerization of Lactones Using Metal Halides and N-Heterocyclic Olefins: Theoretical Insights

“…Additionally, this polarization can be readily tuned and synthesis is usually limited to few and simple steps [ 21 , 22 , 23 ]. Owing to their steadily increasing popularity, NHOs and their structural and catalytic properties have also been the focus of other detailed theoretical studies [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ].…”