Synergistic catalysis: Ionic liquid-modified trinuclear ruthenium clusters enhanced CO2-integrated methoxycarbonylation of ethylene

The ethylene methoxycarbonylation reaction catalyzed by trinuclear ruthenium clusters using CO 2 as the C1 source represents a promising approach for methyl propionate (MeP) synthesis. However, the precise active sites and catalytic mechanism of these versatile catalysts remain incompletely understood. Herein, various ionic liquids (ILs) featuring diverse cationic frameworks and electron-donating groups were synthesized and employed to construct IL-modified trinuclear ruthenium cluster catalysts system (ILM-Ru₃). The investigation into the evolution of active species and the sequential catalytic mechanism during the integrated methoxycarbonylation of ethylene, CO₂, and methanol towards MeP was conducted through experimental and density functional theory (DFT) methods. The results indicated that the cationic framework's structure influences coordination sites and active species distribution. The catalytic activity strongly correlated with the electron-donating capability of cations and the proton-binding capacity of anions. Remarkably, the ILM-Ru₃ system achieved a significantly improved performance (TON=39.8 vs TON=13.7 and selectivity 80.5 % vs 28.2 %) with ≤ 6 % activity variation across 7 cycles outperforming the unmodified system. Complementary spectroscopic techniques including FT-IR, XPS, and 1 H/ 13 C NMR, along with quantum chemistry analysis, provided evidence of carbene–Ru coordination and unveiled the evolution of various Ru-H species. A unique synergistic catalytic mechanism of IRM-Ru 3 enhanced CO₂-integrated methoxycarbonylation that avoids Ru₃(CO)₁₁ regeneration and minimizes cluster dissociation has been proposed, which deeply demonstrating the internal reasons of the improvement in catalytic performance. This approach provides theoretical guidance for the rational design of ruthenium cluster catalysts and development of a green and sustainable MeP process. Examining the influence of the cationic and anion in the contructed ionic liquid-modified trinuclear ruthenium cluster (ILM-Ru₃) catalyst system on the ethylene methoxycarbonylation to methyl propionate using CO₂ as the C1 source, and revealing the essence of the regulatory effect of ionic liquids. Exploring the evolutionary process of species with multiple activities and discussing their roles in catalytic reaction processes using complementary characterizations and quantum chemistry methods. Systematic evaluation demonstrated that the IRM-Ru 3 system exhibited significantly improved performance than Ru 3 (CO) 12 (TON=39.8 vs TON=13.7 and selectivity 80.5 % vs 28.2 %), with excellent stability(≤6 % activity variation after one-month air exposure and 7 reuse cycles). Unveiling a unique synergistic catalytic mechanism of IRM-Ru3 enhanced CO₂-integrated methoxycarbonylation by experiment and theoretical calculations methods: deeply demonstrating the internal reasons of the improvement in catalytic performance.