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

揭示氧气(O2)或二氧化碳(CO2)等小分子活化的机理基础和操作原理是化学科学面临的一个巨大挑战，而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能力，该领域的许多灵感来自生物无机化学。在不同用途的四齿和五齿配体体系中，四氮杂大环化合物已被证明是通过相应的金属络合物来激活O2或CO2的仿生化学中用途广泛的配体。在我们不断努力揭示仿生模型化合物的结构-反应关系的过程中，在之前的资助期间，我们通过连续地用氧、硫、磷和硒原子取代氮供体原子来对四氮杂大环骨架进行定向改变，生成了一个杂原子取代的大环配体体系的文库。只有几个合成的配体的金属络合物可以进行O2/CO2活化反应的能力测试。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活化形成的瞬时中间体的稳定性和反应活性方面起着至关重要的作用。这反过来又对(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。基于我们先前批准的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还原的机理研究的密集和成功的合作研究，特别强调尚未探索的配体系统的配位和催化性质，以及对第一个资助期产生的一些新的活性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普遍机理，目的是探索许多合成的配合物在广泛的新应用领域的潜力。这项研究可能使我们能够深入了解在环境条件下使用廉价和容易获得的第一行过渡金属来设计高效催化剂的先决条件，这些催化剂用于选择性地使未活化的C-H键、O2还原或CO2/H+活化具有官能化作用。

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.