Toward more efficient photochemical CO₂ reduction: Use of scCO₂ or photogenerated hydrides

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• 作者：Mark D. Doherty ; David C. Grills ; James T. Muckerman ; Dmitry E. Polyansky ; Etsuko Fujita
• 关键词：Carbon dioxide reduction ; Small molecule activation ; Photocatalysis ; Renewable hydride donors ; Supercritical CO₂ ; NADH-model ligands
• 刊名：Coordination Chemistry Reviews
• 出版年：2010
• 出版时间：November 2010
• 年：2010
• 卷：254
• 期：21-22
• 页码：2472-2482
• 全文大小：522 K

文摘

Rhenium(I) and ruthenium(II) complexes have been successfully used for photochemical CO₂ reduction to CO or formate. However, a typical turnover frequency for such reactions is <20 h⁻¹ and the formation of reduced species beyond CO or formate is very limited. In the case of the rhenium(I) bipyridyl tricarbonyl system, the key intermediate has been shown to decay with a first-order dependence on [CO₂] to produce CO, which is the rate-determining step. The limited concentration of dissolved CO₂ in organic solvents results in extremely slow CO₂ reduction. To improve the reaction rate, we prepared new CO₂-soluble rhenium(I) bipyridine complexes bearing fluorinated alkyl ligands and investigated their photophysical properties in CH₃CN and supercritical CO₂. We also investigated the properties of a metal complex with an NAD⁺ model ligand, [Ru(bpy)₂(pbn)]²⁺ (bpy = 2,2′-bipyridine, pbn = 2-(2-pyridyl)-benzo[b]-1,5-naphthyridine), and prepared the corresponding NADH-like complex [Ru(bpy)₂(pbnHH)]²⁺ upon MLCT excitation followed by reductive quenching. This species can be used as a renewable hydride donor. The electrochemical and photochemical properties, and the reactivity of these species toward CO₂ reduction were investigated.