Solvent stabilization mechanisms and deactivation pathways of the inert stereo-configuration in iridium carbonyl iodide complexes (Ir(CO)2I2−)

Abstract

Acetic acid is a crucial industrial chemical, and its production via the low-pressure methanol carbonylation process is significantly hindered by the precipitation-induced deactivation of iridium-based catalysts. In this study, the configurational isomerization mechanisms and deactivation pathways of the iridium catalyst (Ir(CO)₂I₂⁻) were systematically investigated using density functional theory (DFT) calculations, with a focus on the key intermediate stereo-configuration (stereo-Ir(CO)₂I₂⁻). The key findings reveal that the cis → trans isomerization barrier is 30.01 kcal mol⁻¹, whereas the trans → cis barrier decreases to 22.10 kcal mol⁻¹, indicating a system preference for establishing dynamic equilibrium through the trans-configuration. The stereo-configuration exhibits a markedly high oxidative addition barrier of 52.33 kcal mol⁻¹ (81.7% and 178.3% higher than those of the cis- and trans-configurations, respectively), demonstrating its kinetic inertness. Within the solvent environment, H₂O/HI induces Ir–I bond elongation beyond 3.1 Å (Mayer bond order <0.5), triggering ligand dissociation. Conversely, multi-carbon molecules like methyl acetate stabilize this configuration via intermolecular interactions, leading to its accumulation at the reaction interface and the formation of a locally supersaturated microenvironment. These insights provide a theoretical basis for designing industrial deactivation-resistant catalysts.