An ETS‐NOCV‐based computational strategies for the characterization of concerted transition states involving CO₂

Abstract

Due to the presence of both a slightly acidic carbon and a slightly basic oxygen, carbon dioxide is often involved in concerted transition states (TSs) with two (or more) different molecular events interlaced in the same step. The possibility of isolating and quantitatively evaluating each molecular event would be important to characterize and understand the reaction mechanism in depth. This could be done, in principle, by measuring the relevant distances in the optimized TS, but often distances are not accurate enough, especially in the presence of many simultaneous processes. Here, we have applied the Extended Transition State-Natural Orbital for Chemical Valencemethod (ETS-NOCV), also in combination with the Activation Strain Model (ASM) and Energy Decomposition Analysis (EDA), to separate and quantify these molecular events at the TS of both organometallic and organic reactions. For the former, we chose the decomposition of formic acid to CO 2 by an iridium catalyst, and for the latter, a CO 2 -mediated transamidation and its chemical variations (hydro-and aminolysis of an ester) as case studies. We demonstrate that the one-to-one mapping between the "molecular events" and the ETS-NOCV components is maintained along the entire lowest energy path connecting reactants and products around the TS, thus enabling a detailed picture on the relative importance of each interacting component.The methodology proposed here provides valuable insights into the effect of different chemical substituents on the reaction mechanism and promises to be generally applicable for any concerted TSs.

DFT Study of the Adsorption and SERS of Pyridine on M10N10 (M, N = Cu, Ag) Tetrahedral Clusters

“…The deformation density isosurface maps were obtained according to the extended-transition-state natural orbitals for chemical valence (ETS-NOCV) − partitioning scheme. In the ETS-NOCV scheme, the electron density rearrangement taking place upon complex formation is defined with respect to a reference called the promolecule state (ρ 0 ( r )). , Orbital interaction results in variation of electron density, which can be represented as orbital deformation density (Δρ orb ), Δ ρ orb = ρ­( r ) – ρ 0 ( r ), where ρ­( r ) corresponds to the electron density of the complex (ψ AB ). The total deformation density (Δρ) contains the orbital and the Pauli deformation terms …”

Widening the Landscape of Small Molecule Activation with Gold‐Aluminyl Complexes: A Systematic Study of E−H (E=O, N) Bonds, SO2 and N2O Activation

“…Unfortunately, as we have previously demonstrated, the IRC approach is unable to yield the correct connectivity between transition states and minima in this context due to the flat and complex topology of the Potential Energy Surface (PES). [3,4,76] This issue of the IRC approach has also been previously discussed within a more general perspective in the literature, see for instance ref. [77].…”

“…Note that generally, as advised for the application of the Activation Strain Model, [47] the use of Intrinsic Reaction Coordinate (IRC) calculations to monitor the evolution of distortion and interaction contributions along the reaction coordinate is recommended. Unfortunately, as we have previously demonstrated, the IRC approach is unable to yield the correct connectivity between transition states and minima in this context due to the flat and complex topology of the Potential Energy Surface (PES) [3,4,76] . This issue of the IRC approach has also been previously discussed within a more general perspective in the literature, see for instance ref.…”

Cooperative small molecule activation by apolar and weakly polar bonds through the lens of a suitable computational protocol

“…It has been discussed in the literature that a single IRC cannot define a particular preferred reaction pathway when the potential energy surface is flat 87 and we already encountered the same issue before when studying computationally CO 2 activation processes. 88…”

“…It has been discussed in the literature that a single IRC cannot define a particular preferred reaction pathway when the potential energy surface is flat 87 and we already encountered the same issue before when studying computationally CO 2 activation processes. 88 The case of the carbon dioxide activation by a gold-aluminyl complex is a textbook example of this type of situation. We extensively discussed the particularly complex topology of the flat PES in the case of this reaction, and this prevented the possibility for us to use the IRC to help providing insights into the connectivity between transition states and local minima.…”