Todorova Tanya K, Huan Tran Ngoc, Wang Xia, Agarwala Hemlata, Fontecave Marc
Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, Collège de France , Université Paris 6 , 11 Place Marcelin Berthelot , 75231 Paris Cedex 05, France.
Inorg Chem. 2019 May 20;58(10):6893-6903. doi: 10.1021/acs.inorgchem.9b00371. Epub 2019 May 3.
The photochemical reduction of CO to formic acid catalyzed by a series of [Rh(4,4'-R-bpy)(Cp*)Cl] and [Rh(5,5'-COOH-bpy)(Cp*)Cl] complexes (Cp* = pentamethylcyclopentadienyl, bpy = 2,2'-bipyridine, and R = OCH, CH, H, COOCH, CF, NH, or COOH) was studied to assess how modifications in the electronic structure of the catalyst affect its selectivity, defined as the HCOOH:H product ratio. A direct molecular-level influence of the functional group on the initial reaction rate for CO versus proton reduction reactions was established. Density functional theory computations elucidated for the first time the respective role of the [RhH] and [Cp*H] tautomers, recognizing rhodium hydride as the key player for both reactions. In particular, our calculations explain the observed tendency of electron-donating substituents to favor CO reduction by means of decreasing the hydricity of the Rh-H bond, resulting in a lower hydride transfer barrier toward formic acid production as compared to substituents with an electron-withdrawing nature that favor more strongly the reduction of protons to hydrogen.
研究了一系列[Rh(4,4'-R-联吡啶)(五甲基环戊二烯基)Cl]和[Rh(5,5'-羧基联吡啶)(五甲基环戊二烯基)Cl]配合物（Cp* = 五甲基环戊二烯基，bpy = 2,2'-联吡啶，R = OCH₃、CH₃、H、COOCH₃、CF₃、NH₂或COOH）催化的CO光化学还原为甲酸的反应，以评估催化剂电子结构的修饰如何影响其选择性，选择性定义为HCOOH:H产物比。确定了官能团对CO与质子还原反应初始反应速率的直接分子水平影响。密度泛函理论计算首次阐明了[RhH]和[Cp*H]互变异构体各自的作用，认识到氢化铑是这两个反应的关键参与者。特别是，我们的计算解释了观察到的供电子取代基通过降低Rh-H键的酸度来促进CO还原的趋势，与更强烈促进质子还原为氢的吸电子性质取代基相比，这导致向甲酸生成的氢化物转移势垒更低。
