Cyclam Based Transition Metal Complexes and Their Performance in Established and New Application Areas

揭示小分子如二氧（O2）或二氧化碳（CO2）活化的机制基础和操作原理对化学科学来说是一个巨大的挑战，解决这些挑战对于设计和开发高效催化剂至关重要。由于自然界主要使用金属离子来激活这些相对惰性的分子并调节它们的反应性，因此该领域的许多灵感来自生物无机化学。在不同利用的四齿和五齿配体体系中，四氮杂环环体已被证明是通过相应的金属配合物激活O2或CO2的仿生化学中的通用配体。在我们不断努力揭示仿生模型配合物的结构-反应性关系的过程中，在之前的资助期内，我们通过将氮给体原子连续替换为氧、硫、磷和硒原子，对四氮杂环框架进行了定向改变，生成了一个杂原子取代的大环配体体系库。只有少数合成配体的金属配合物可以测试它们进行O2/CO2活化反应的能力。我们发现结合的O2/CO2与辅助配体的二次相互作用在控制O2/CO2活化形成的瞬态中间体的稳定性和反应性方面起着至关重要的作用。这些因素反过来又对（电）催化CO2/O2还原反应的产物选择性和过电位产生重大影响。基于我们先前获得的dfg提案的结果，我们打算继续我们正在进行的关于过渡金属介导的CO2/O2还原的机制研究的深入和成功的合作研究，特别强调尚未探索的配体系统的协调和催化性质，以及在第一个资助期产生的一些新型反应中间体的详细光谱表征。主要目的是更详细地了解小分子活化的主要机制，目的是探索许多合成配合物在广泛的新应用领域的潜力。这项研究可能为设计高效催化剂提供重要的先决条件，这些催化剂可以在环境条件下使用廉价且容易获得的第一排过渡金属来选择性官能化非活化的C-H键、O2还原或CO2/H+活化。

Unraveling the mechanistic basis and operational principles of the activation of small molecules like dioxygen (O2), or carbon dioxide (CO2) represents a formidable challenge to the chemical sciences, and addressing these challenges is essential for the design and development of efficient catalysts. Since nature mostly uses metal ions to activate these relatively inert molecules and modulate their reactivity, much inspiration for the field has come from bioinorganic chemistry. Among the different utilized tetradentate and pentadentate ligand systems, tetraazamacrocyclic cyclams have proved to be versatile ligands in the biomimetic chemistry of O2 or CO2 activation via the corresponding metal complexes. In our continuous effort to uncover structure-reactivity relationships of biomimetic model complexes, in the previous funding period, we performed a directed alteration of the tetraazamacrocyclic framework by consecutive substitution of the nitrogen-donor atoms by oxygen, sulfur, phosphorous and selenium atoms to generate a library of heteroatom substituted macrocyclic ligand systems. The metal complexes of only a few of the synthesized ligands could be tested for their ability to perform O2/CO2 activation reactions. We showed that secondary interactions of the bound O2/CO2 with the ancillary ligands play a vital role in controlling the stability and reactivity of the transient intermediates formed upon O2/CO2 activations. These, in turn, exerted significant influence on the product selectivity and the overpotential of the (electro)catalytic CO2/O2 reduction reactions. Building on our results from the previously granted DFG-proposal, we intend to continue our ongoing intensive and successful collaborative studies on the mechanistic investigation of the transition metal-mediated CO2/O2 reductions, paying particular emphasis to the coordination and catalytic properties of the yet unexplored ligand systems, and to the detailed spectroscopic characterization of some of the novel reactive intermediates generated in the first funding period. The main aim is to understand the prevailing mechanisms of small molecule activation in more detail, with the aim of exploring the potential of many of the synthesized complexes in a wide range of new application areas. This study may allow vital insights into the prerequisites necessary for the design of efficient catalysts for the selective functionalization of unactivated C–H bonds, O2 reduction, or CO2/H+ activations by using cheap and readily available first-row transition metals under ambient conditions.