Mechanism of the photoreduction of carbon dioxide catalyzed by the benchmarking rhenium dimethylbipyridine complexes; operando measurements by XAFS and FT-IR

The photoreduction of CO2 catalyzed by [fac-Re(dmbpy)(CO)(3)Cl] was precisely investigated through operando measurements of X-ray absorption fine structure spectroscopy (XAFS) and laser-flash FT-IR transient spectroscopy. In the early stage of the photoreaction, Re-0-species assigned as penta-coordinated complex, [Re-0(dmbpy)(CO)(3)], appeared and a delayed rise of Re-II-species, [Re-II(dmbpy)(CO)(3)CO2] (3)/[Re-II(dmbpy)(CO)(3)COOH](+) (3'), were observed in XAFS measurements. The valence state of Re-center in the catalytic cycle changed as Re-I -> Re-0 -> Re-II to be a clear evidence of an oxidative addition of CO2 to the Re-0 center. In the laser-flash induced FT-IR measurements, a rise and decay of 3 followed by a delayed rise and decay of 3' was observed. The second electron transfer from the carbon radical of triethylamine (TEA(center dot)) to 3' induced the formation of [Re-I(dmbpy)(CO)(4)](+) through [Re-I(dmbpy)COOH]. The rate determining step of the catalytic cycle was revealed to be the protonation process of forming 3' from 3. (C) 2021 The Author(s). Published by Elsevier Inc.

Automated summary

The photoreduction of CO2 catalyzed by [fac-Re(dmbpy)(CO)(3)Cl] was precisely investigated using operando X-ray absorption fine structure spectroscopy (XAFS) and laser-flash FT-IR transient spectroscopy. The study observed the appearance of Re-0 species and a delayed rise of Re-II species in the early stage of the photoreaction. Additionally, the protonation process of forming Re-II was revealed as the rate determining step of the catalytic cycle.