Coordination Chemical Scaffolds for Dual Proton Coupled Photoelectron Transfer

用于双质子耦合光电子转移的配位化学支架

• 批准号: 404422233
• 负责人: Professor Dr. Wolfram W. Seidel
• 金额: --
• 依托单位: Metallorganische Chemie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/404422233?language=en
• 关键词: Coordination; Chemical; Scaffolds; Dual; Proton

Photocatalysts are potentially susceptible to decomposition because chemical bonds in excited states are generally weakened. This immanent problem of photocatalysis is even increased by long-living excited states, which are actually sought for in order to reach high conversion rates. Most of the successful strategies to solve this dilemma make use of charge separation (CS) by intra- or intermolecular electron transfer, which leads in turn to the formation of radicals. In photocatalysis almost always radical chemistry is involved, which can cause undesired side reactions. An alternative approach to avoid the occurrence of radicals or at least to avoid intermolecular radical reactions is based on a consecutive dual electron transfer. However, the generally low probability of a second excitation even for long life times of the first excited state turn this idea to an ambitious objective. However, with respect to the chinone/hydrochinone pair in natural photosynthesis and the NAD+/NADH pair as versatile biochemical redox agent, two-electron processes in combination with proton-coupled electron transfers seem to be biomimetic in converting light into usable chemical energy.The assembly of classical photo-active centres like a Ir(III) or Ru(II) polypyridine complex units with (i) two redox-active, potentially electron donating metalloligands and (ii) with a Brønstedt-basic two-electron acceptor as NAD/NADH model in an Y-shaped arrangement is the essential concept of the project. Within this frame, novel redox-active N,C-κ2-donating ligands including an alkyne complex moiety, which bears terminal donor functionalities, are the central invention. The redox activity of the electron donating ligands is based on the redox activity of the side-on alkyne coordinated metal. The inherent problem of unproductive charge recombination (back electron transfer) of a comparatively compact CS triad is addressed by chemical excited state trapping by protons and subsequent radical pair formation. A 2,3-5’,6’-fused pyridylphenanthroline derivative was chosen as an appropriate NAD/NADH model ligand.The analytical proof of a dual proton coupled photoelectron transfer represents the specific incentive of the project. In addition, potential photo-NAD/NADH systems could be thought as catalytically active, powerful synthetic tools, which transfer formal H atom equivalents from weak reducing agents in the presence of weak proton donors to organic substrates like ketones. The original light excitation energy is than transformed in chemical bond energy by increasing the hydride donor or reducing potential of the starting material by the intermediate catalyst. However, a profound understanding of the mutual interaction of photodynamic behaviour and elementary proton transfer kinetics are paramount.

光催化剂可能容易分解，因为激发态的化学键通常会减弱。光催化的这一内在问题甚至因长寿命的激发态而加剧，而实际上为了达到高转化率而需要这种激发态。大多数解决这一困境的成功策略都利用分子内或分子间电子转移的电荷分离（CS），这反过来又导致自由基的形成。在光催化中几乎总是涉及自由基化学，这可能会导致不需要的副反应。避免自由基发生或至少避免分子间自由基反应的另一种方法是基于连续的双电子转移。然而，即使第一激发态的寿命很长，第二次激发的概率通常也很低，这使得这个想法成为一个雄心勃勃的目标。然而，就自然光合作用中的醌/氢醌对和作为通用生化氧化还原剂的NAD+/NADH对而言，双电子过程与质子耦合电子转移相结合似乎在将光转化为可用化学能方面具有仿生性。经典光活性中心如Ir(III)或Ru(II)聚吡啶络合物单元的组装 该项目的基本概念是（i）两种氧化还原活性、潜在电子供给金属配体和（ii）以 Brønstedt 碱性双电子受体作为 Y 形排列的 NAD/NADH 模型。在此框架内，新型氧化还原活性N,C-κ2-供体配体（包括带有末端供体功能的炔烃复合物部分）是核心发明。给电子配体的氧化还原活性基于侧链炔配位金属的氧化还原活性。相对紧凑的 CS 三元组的非生产性电荷复合（反向电子转移）的固有问题通过质子的化学激发态捕获和随后的自由基对形成来解决。选择2,3-5',6'-稠合吡啶基菲咯啉衍生物作为合适的NAD/NADH模型配体。双质子耦合光电子转移的分析证明代表了该项目的具体动机。此外，潜在的光NAD/NADH系统可以被认为是具有催化活性的强大合成工具，它可以在弱质子供体存在的情况下将形式的H原子当量从弱还原剂转移到酮等有机底物。然后，通过增加氢化物供体或通过中间催化剂降低起始材料的电势，将原始光激发能转化为化学键能。然而，对光动力行为和基本质子转移动力学的相互作用的深刻理解是至关重要的。