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.

光催化剂潜在地易于分解，因为激发态中的化学键通常被削弱。长寿命的激发态甚至会增加这种不确定性问题，实际上，为了达到高转化率，人们正在寻找长寿命的激发态。解决这一难题的大多数成功策略都是通过分子内或分子间电子转移来利用电荷分离（CS），这反过来又导致自由基的形成。在化学反应中，几乎总是涉及自由基化学，这可能导致不希望的副反应。避免出现自由基或至少避免分子间自由基反应的替代方法是基于连续的双电子转移。然而，即使对于第一激发态的长寿命，第二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，相对于自然光合作用中的醌/对苯二酚对和作为通用生物化学氧化还原剂的NAD+/NADH对，与质子耦合电子转移组合的双电子过程似乎在将光转化为可用化学能方面是仿生的。潜在的电子捐赠金属配体和（ii）与Brønstedt基本的双电子受体作为NAD/NADH模型在Y形排列是该项目的基本概念。在该框架内，包括带有末端供体官能团的炔络合物部分的新型氧化还原活性N，C-κ2-供体配体是中心发明。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。非生产性的电荷重组（背电子转移）的一个比较紧凑的CS三元组的固有问题是解决由质子和随后的自由基对形成的化学激发态捕获。选择了一种2，3 - 5 '，6'-稠合吡啶基菲咯啉衍生物作为NAD/NADH模型配体，通过分析证明了该模型配体具有双质子耦合的光电子转移，这是本课题的具体动机。此外，潜在的光NAD/NADH系统可以被认为是催化活性的，强大的合成工具，其在弱质子供体存在下将形式H原子当量从弱还原剂转移到有机底物如酮。然后，通过中间体催化剂增加氢化物供体或还原起始材料的电势，将原始光激发能转化为化学键能。然而，光动力学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。