Redoxneutral Propargylic CH-Activation: from Mechanistic Investigations towards better Catalysts

本项目将继续对Rh催化丙叉醛C-H活化的机理进行研究。在原子经济性、氧化还原中性催化存在问题的情况下，以碳酸和末端烯烃或烯为原料可合成烯丙基酯和烯醇酸酯。在以DIOP为手性配体的支链烯丙酸酯的合成中，对映体过量可达96%。在B.Breit和D.Heller的合作下，确定了催化循环的休眠状态。通过核磁共振、拉曼光谱、X-射线分析、质谱分析等手段对该关键中间体进行了表征。此外，通过原位红外光谱和核磁共振光谱确定了催化转化的定性速率定律。在这些研究中，检测到了一种催化剂，它抑制了与炔底物的反应。这些实验得到了DFT计算的支持，这与研究结果相吻合。在这次合作中获得的结果被用来改进拟议的机制。B.Breit和D.Heller的成功合作将在这里介绍的项目的基础上继续下去。该项目的主要目标是进一步从机理上研究酯的形成，以及将所提出的机理转移到类似的铑催化的含氮原亲核试剂的烯丙基胺的形成上。在这个项目中，将研究炔烃和烯烃对催化反应的影响，特别是催化剂抑制的来源。此外，应详细解释观察到的对不同酯类产物的化学选择性，这取决于所选择的配体，并应调查产物与Rh配体络合物结构的关系。对Rh催化的烯丙基胺与苯胺和苯并三唑形成的机理的研究应表明，不同的亲核原分子所提出的机理是否有共同的碱基，或者每个亲核原分子是否都有自己独特的机理。在研究苯并三唑与末端联烯加成的过程中，观察到的对N1-和N2-产物的区域选择性取决于配体的原因。机理研究将包括核磁共振、IR、UV/VIS和拉曼光谱、结晶学和质谱学实验，并将辅之以密度泛函计算。

With this project the mechanistic investigations on rhodium catalyzed propargylic C-H-activation shall be continued. With the atom economic, redox neutral catalysis in question, allylic esters and enolesters can be synthesized starting form carbon acids and terminal alkynes or allenes. In the synthesis of branched allylic esters with DIOP as chiral ligand enantiomeric excesses up to 96% can be achieved. In the cooperation of B. Breit and D. Heller, the resting state of the catalytic cycle was identified. This key intermediate was characterized by means of NMR- and Raman spectroscopy, as well as by X-ray analysis and mass spectrometry. In addition, a qualitative rate law for the catalytic transformation was determined through in-situ IR- and NMR-spectroscopy. In these investigations a catalyst inhibition in reactions with the alkyne substrate was detected. The experiments were supported by DFT-calculations, which matched the findings. The results obtained in this collaboration were used to refine the proposed mechanism. The successful cooperation of B. Breit and D. Heller will be continued on basis of the project presented here. The main objectives of this project are further mechanistic investigations of the formation of esters as well as the transferability of the proposed mechanism to the analogous rhodium catalyzed formation of allylic amines with nitrogen-containing pronucleophiles. Within this project the effects of alkynes and allenes on the catalytic reaction, especially the origin of the inhibition of the catalyst, will be examined. In addition, an explanation for the observed chemoselectivity towards different ester products depending on the chosen ligand shall be elaborated and the relation of the product to the structure of the rhodium ligand complex shall be investigated. The mechanistic investigations of the rhodium catalyzed formation of allylic amines with anilines and benzotriazoles shall indicate whether the proposed mechanisms for the different pronucleophiles share a common base or if every pronucleophile has its own unique mechanism. During the investigations of the addition of the benzotriazole to terminal allenes, a reason for the observed regioselectivity towards the N1- and N2-product depending on the ligand will be saught after. The mechanistic investigations will consist of NMR-, IR-, UV/Vis-, and Raman-spectroscopic, crystallographic and mass spectrometric experiments and will be complemented with DFT calculations.