Computationally Designed 1,2,4-Triazolylidene-Derived N-Heterocyclic Olefins for CO2 Capture, Activation, and Storage

Abstract

In this article, triazolylidene-derived N-heterocyclic olefins (trNHOs) are designed using computational quantum tools, and their potential to promote CO₂ sequestration is tested and discussed in detail. The low barrier heights related to the trNHO-mediated process indicate that the tailored compounds are very promising for fast CO₂ sequestration. The systematic analysis of the presence of distinct substitutes at different N positions of the trNHO ring allows us to rationalize their effect on the carboxylation process and reveal the best N-substituted trNHO systems for CO₂ sequestration and improved trNHO carboxylates for faster CO₂ capture/release.

Scheme 1. CO₂ Capture by NHO Yielding NHO–CO₂ Adducts

Figure 1

Overview of the present study: generic structure of an imidazolylidene-derived NHO (NHO), a triazolylidene-derived NHO (trNHO), reference NHO, reference trNHO, and the explored substituents (R).

Figure 2

Relative energy profiles of the NHO + CO₂ and trNHO + CO₂ carboxylation processes obtained using the E_corrected^{DLPNO-CCSD(T)} energies and NCI analysis using its color scale: green for weak interactions, red for strong nonbonded overlaps, and blue for strong attractive interactions; all energies are given in kcal mol^–1 with respect to the separated reactants.

Figure 3

Six active IBOs for the NHO- and trNHO-mediated processes; electron pairs are IBOs of the same color. The active IBO that changed the most along the reaction path, numbered as 1, has its fraction of electrons assigned to individual atoms shown in parentheses.

Figure 4

Relative energy profiles for the carboxylation process of (A) trNHO-1e-N²-1j-N⁴, (B) trNHO-1e-N²-1i-N⁴, and (C) trNHO-1e-N²-1e-N⁴. For completeness, the energetic of the reaction between the reference system, trNHO, and CO₂ is also indicated in (D). The energies are obtained using the E_corrected^{DLPNO-CCSD(T)} values and are given in kcal mol^–1 with respect to the separated reactants.

Figure 5

IBO related to C–C bond formation between CO₂ and trNHO systems; the fractions of electrons assigned to individual atoms are shown in parentheses. The carbon atoms are labeled as indicated in Figure 3.

Figure 6

Differences in the components of the interaction energy and distortion energy for TSs trNHO_TS-1e-N²-1e-N⁴, trNHO_TS-1e-N²-1i-N⁴, and trNHO_TS-1e-N²-1j-N⁴ with respect to the reference system trNHO_TS. X = es, ex, rep, pol, disp, int, and dist.