Abstract：
Most redox processes that break/form bonds involve net 2e- changes, and many are coupled to protons. Yet most proton-coupled electron transfer (PCET) studies focus on 1e-/1H+ reactions. Reported here is a family of molecular models that undergo tunable 2e-/2H+ redox changes. Complexes [(X2bpy)RuII(en*)2](PF6)2 and [(X2bpy)RuIV(en*-H)2](PF6)2 have been synthesized with bpy = 2,2\'-bipyridine with 4,4\'-subtitutions X = -NMe2, -OMe, -Me, -H, -CF3; and en* = 2,3-dimethyl-2,3-butanediamine. They have been characterized by IR, UV-vis, and NMR spectroscopies, XRD, electrochemistry, mass spectrometry, DFT and (TD)DFT computations. The introduction of electron-withdrawing and donating groups at the 4,4\'-position of the bpy ligand affects the complexes\' redox potentials, pKa\'s, and Bond Dissociation Free Energies (BDFEs) of the N-H bonds in the en* ligands. The average BDFEs for the overall 2e-/2H+ PCET span over 5 kcal/mol. Notably, these complexes all show marked potential inversion over an extended range, ΔpKa > 25 units and ΔE0 > 1.4 V. Potential inversion remains despite the electronic influence of bpy\'s substitutions which regulate N-H properties several bonds apart by trans-effect over dπ-molecular orbitals at Ru-center. The experimental and computational results presented in this work support the presence of strong coupling between electrons and protons, for modelling insights of 2e-/2H+ transfer reactivity.
摘要：
大多数破坏/形成键的氧化还原过程都涉及净2e-变化，许多与质子耦合。然而,大多数质子耦合电子转移(PCET)研究集中于1e-/1H+反应。这里报道的是经历可调的2e-/2H+氧化还原变化的分子模型家族。已合成配合物[（X2bpy）RuII（en*）2]（PF6）2和[（X2bpy）RuIV（en*-H）2]（PF6）2，bpy=2,2'-联吡啶，4'-取代度X=-NMe2，-OMe，-我,-H,-CF3;和en*=2,3-二甲基-2,3-丁二胺。它们的特征是IR，UV-vis,和核磁共振波谱,XRD,电化学,质谱,DFT和(TD)DFT计算。在bpy配体的4,4'-位置引入吸电子和供体基团会影响配合物的氧化还原电位，pKa\'s,和en*配体中N-H键的键解离自由能(BDFE)。整个2e-/2H+PCET的平均BDFE跨度超过5kcal/mol。值得注意的是,这些复合物在扩展的范围内都显示出明显的电位反转，ΔpKa>25个单位，ΔE0>1.4V。尽管有bpy取代的电子影响，其通过在Ru中心的dπ分子轨道上的反式效应调节N-H性质，几个键分开。这项工作中提出的实验和计算结果支持电子和质子之间存在强耦合，用于2e-/2H+转移反应性的建模见解。
