Exploring CO2 activation mechanisms with triphenylphosphine derivatives: insights from energy decomposition and deformation density analyses†

Abstract

This study focuses on the reaction mechanisms involving triphenylphosphine (PPh₃) derivatives, benzyne, and CO₂, giving mechanistic insights into two competing pathways: Path a, which involves direct C–P bond formation, and Path b, which progresses via a [2 + 2] cycloaddition. Comprehensive computational analysis by energy decomposition analysis (EDA) and deformation density insights was employed to elucidate the electronic and steric factors influencing the reactivity and selectivity of PPh₃ derivatives. The results reveal that Path b is energetically and kinetically favored. In Path a, substantial repulsive interactions (ΔE_rep), especially for electron-withdrawing substituents, hinder C–P bond formation, making this pathway unfavorable, while Path b benefits from compensatory effects between interaction energies, with electron-releasing para-substituents, such as NHMe and OMe, increasing stabilization by enhancing ΔE_orb contributions. Substituents in meta positions show greater distortion energies (ΔE_dist), which limit their stabilizing effects compared to para-substituents. The deformation density analysis of transition states (TS1(b) and TS2(b)) emphasizes the crucial role of Pauli deformation (Δρ^Pauli) and orbital deformation (Δρ^Orb) in modulating stability. Para-substituents exhibit stronger electronic effects, reducing ΔE_int more effectively than meta-substituents, which increase ΔE_dist. This positional dependence underscores the importance of substituent design in optimizing reactivity.