Influence of the CH/B replacement on the Reactivity of Boranthrene and Related Compounds

A theoretical study of the reaction of borata derivatives of benzene, anthracene and pentacene with CO2

A theoretical study of the reaction between several borataacenes (1-methylboratabenzene, 9-methyl-9-borataanthracene and cis and trans diboratapentacene) and CO2 has been carried out at the M06-2X computational level. The influence of a counterion (potassium cation), the cation complexation by 18-crown-6-ether and solvent effects have been explored. The computational results predict anti/syn selectivity as found experimentally in the cis- and trans-diboratapentacene reaction with CO2 (Baker et al., J. Am. Chem. Soc., 2023, 145, 2028).

Use of 5,10-Disubstituted Dibenzoazaborines and Dibenzophosphaborines as Cyclic Supports of Frustrated Lewis Pairs for the Capture of CO2

The reactivity of 5,10-disubstituted dibenzoazaborines and dibenzophosphaborines towards carbon dioxide was studied at the DFT, M06-2X/def2-TZVP, computational level. The profile of this reaction comprises of three stationary points: the pre-reactive complex and adduct minima and the transition state(TS) linking both minima. Initial results show that dibenzoazaborines derivatives are less suitable to form adducts with CO₂ than dibenzophosphaborine systems. The influence of the basicity on the P atom and the acidity on the B center of the dibenzophosphaborine in the reaction with CO₂ was also explored. Thus, an equation was developed relating the properties (acidity, basicity and boron hybridization) of the isolated dibenzophosphaborine derivatives with the adduct energy. We found that modulation of the boron acidity allows to obtain more stable adducts than the pre-reactive complexes and isolated monomers.

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

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 Valence‐method (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 CO₂ by an iridium catalyst, and for the latter, a CO₂‐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.