VII. Analysis of the activation energy for isomerization step To investigate the proton transfer as the RDS in the isomerization step proposed by Wang et al.4 (Scheme S3.1), we performed the activation energy analysis for three cations: MM, n-Pr n-Pr, and i-Pr i-Pr. The following steps were considered to evaluate the activation energy: a) Geometries for cations(compounds i in Figure S3.12), reduced cations ImH0 (compounds ii in Figure S3.12), ImHCO2 adducts (compounds iii in Figure S3.12), and intermediates ImCOOH (compounds iv in Figure S3.12) were optimized stepwise. Figure S3.12 shows the geometry optimized for all 4 compounds for MM, n-Pr n-Pr, and i-Pr i-Pr cations. b) In order to find an initial guess for the transition state, we performed a potential energy surface scan (PES) for proton transfer proposed in the isomerization step (from compound iii to compound iv). Scheme S3.1. Step-wise electron-proton transfer to CO2 mediated by imidazolium cation. Catalytic cycle proposed by Wang. et al.4 for cation mediated sequential electron-proton transfer to CO2. Proton transfer in the isomerization from ImHCO2 adduct to ImCOOH was proposed as the rate-determining step.
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