Direct Detection of Key Reaction Intermediates in Photochemical CO2 Reduction Sensitized by a Rhenium Bipyridine Complex

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• 作者：Youki Kou ; Yu Nabetani ; Dai Masui ; Tetsuya Shimada ; Shinsuke Takagi ; Hiroshi Tachibana ; Haruo Inoue
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 23, 2014
• 年：2014
• 卷：136
• 期：16
• 页码：6021-6030
• 全文大小：543K
• 年卷期：v.136,no.16(April 23, 2014)
• ISSN：1520-5126

文摘

Photochemical CO₂ reduction sensitized by rhenium鈥揵ipyridyl complexes has been studied through multiple approaches during the past several decades. However, a key reaction intermediate, the CO₂-coordinated Re鈥揵ipyridyl complex, which should govern the activity of CO₂ reduction in the photocatalytic cycle, has never been detected in a direct way. In this study on photoreduction of CO₂ catalyzed by the 4,4鈥?dimethyl-2,2鈥?bipyridine (dmbpy) complex, [Re(dmbpy)(CO)₃Cl] (1), we successfully detect the solvent-coordinated Re complex [Re(dmbpy)(CO)₃DMF] (2) as the light-absorbing species to drive photoreduction of CO₂. The key intermediate, the CO₂-coordinated Re鈥揵ipyridyl complex, [Re(dmbpy)(CO)₃(COOH)], is also successfully detected for the first time by means of cold-spray ionization spectrometry (CSI-MS). Mass spectra for a reaction mixture with isotopically labeled ¹³CO₂ provide clear evidence for the incorporation of CO₂ into the Re鈥揵ipyridyl complex. It is revealed that the starting chloride complex 1 was rapidly transformed into the DMF-coordinated Re complex 2 through the initial cycle of photoreduction of CO₂. The observed induction period in the time profile of the CSI-MS signals can well explain the subsequent formation of the CO₂-coordinated intermediate from the solvent-coordinated Re鈥揵ipyridyl complex. An FTIR study of the reaction mixture in dimethyl sulfoxide clearly shows the appearance of a signal at 1682 cm^鈥?, which shifts to 1647 cm^鈥? for the ¹³CO₂-labeled counterpart; this is assigned as the CO₂-coordinated intermediate, Re^II鈥揅OOH. Thus, a detailed understanding has now been obtained for the mechanism of the archetypical photochemical CO₂ reduction sensitized by a Re鈥揵ipyridyl complex.