Electron-rich phosphines, switchable lewis (super)acids and cooperative metal complexes: new prospects for the activation of CO2, N2, H2, N2O and SO2 and their utilization as synthetic building blocks

激活CO2、N2、H2、N2O和SO2等小分子以实现高能效化学转化是当前研究的关键挑战。目前的项目涉及开发利用这些分子作为合成构件并将其转化为化学能量储存燃料的新方法。在我们之前的研究中，我们发现通过在磷原子上连接强供体取代基R （R =咪唑啉-2-基氨基）可以得到非常富电子的膦PR3。所得到的膦是均相催化下的强配体，它们形成具有低能垒的可逆CO2加合物。在此基础上，本项目提出了具有优化性能（光开关性、水稳定性、可变立体性和电子性能）的新型给体取代基R的合成方法。这些R取代基构成了以下三个子项目的常见合成构件：子项目1提出用不带电的强刘易斯碱活化CO2和SO2，目标是在温和条件下刘易斯碱催化CO2的官能化和SO2中SO的控制释放。在这方面，将开发具有可变空间和电子性质的磷化氢、磷化氢氧化物和胍基，并研究它们形成CO2和SO2加合物的能力。子项目2涉及使用具有可切换刘易斯酸度的新型刘易斯（超级）酸活化H2， N2O， CO2和N2。在这种情况下，立体保护，三角平面磷和硼阳离子将被制备。这些路易斯酸的特点是，它们的路易斯酸度可以通过紫外线照射或质子化而增加。目的是通过络合路易斯酸来激活N2O、CO2和SO2，并使它们随后与弱亲核底物（如烯烃、烷基或芳香族化合物）发生反应。反应产物从路易斯酸中解放出来应通过路易斯酸的转换来完成。在子项目3中，提出了N2和H2在Cu、Au、Ru和Fe配合物上的协同活化。特定配体的设计和多金属结构的生成将允许N2配合物与铸造金属的分离。第二个重点是利用Ru和Fe螯合物催化N2加氢生成NH3。

The activation of small molecules such as CO2, N2, H2, N2O and SO2 for energy-efficient chemical transformations is a key challenge of current research. The present project is concerned with the development of new methods for the utilization of these molecules as synthetic building blocks and for their transformation into fuels for chemical energy storage. In our previous studies we showed that very electron-rich phosphines PR3 were obtained by attaching strong donor substituents R (R = imidazolin-2-ylidenamino) at the phosphorus atom. The resulting phosphines are powerful ligands in homogeneous catalysis and they form reversible CO2 adducts with low energy barriers. Based on these results, the synthesis of new donor substituents R with optimized properties (photoswitchability, water stability, variable steric and electronic properties) is proposed in the present project. These R substituents constitute the common synthetic building blocks in the following three subprojects: In subproject 1 the activation of CO2 and SO2 with uncharged strong Lewis bases is proposed targeting towards the Lewis base-catalyzed functionalization of CO2 and the controlled release of SO from SO2 under mild conditions. In this respect, phosphines, phosphine oxides and guanidine bases with variable steric and electronic properties will be developed, and their ability to form CO2 and SO2 adducts will be investigated. Subproject 2 is concerned with the activation of H2, N2O, CO2 and N2 using novel Lewis (super)acids with switchable Lewis acidity. In this context, sterically protected, trigonal planar phosphorus and boron cations will be prepared. These Lewis acids comprise the feature that their Lewis acidity can be increased by irradiation with UV light or by protonation. The goal is to activate N2O, CO2 and SO2 by complexation to the Lewis acids and to enables their subsequent reaction with weakly nucleophilic substrates such as alkenes, alkines or aromatic compounds. Liberation of the reaction products from the Lewis acid shall be accomplished by switching of the Lewis acidity. In subproject 3 the cooperative activation of N2 and H2 at Cu, Au, Ru and Fe complexes is proposed. Specific ligand design and the generation of polymetallic structures shall allow for the isolation of N2 complexes with the coinage metals. A second focus lies on the catalytic hydrogenation of N2 to form NH3 using Ru and Fe pincer complexes.