Carbene- and phosphine-substituted Biradicaloids for sustainable Catalysis (CarPhoSCat)

由于它们对环境和经济的影响，人们一直有兴趣用更富含地球的3D对应物(贱金属)来取代均相催化中的贵金属，或者使用主族元素化合物来模拟过渡金属的行为。为此，开发专门的配基系统是必要的。一般来说，它们可以分为两类：氧化还原活性配体，其中配体本身参与电子转移过程，从而实现与贵金属催化剂相关的典型的两电子氧化还原步骤；以及具有强碱性中心的配体，有助于底物中共价键的异解断裂(合作键激活)。尽管使用这两个概念取得了许多令人印象深刻的成就，但均相主族和贱金属催化剂在活性和选择性方面往往不如贵金属催化剂。CarPhoSCat研究项目的目标是通过开发具有卡宾和膦取代的双自由基配体的主基和贱金属催化剂来解决和克服一些限制。这类配体具有强烈的金属-配体相互作用、支持氧化还原活性、灵活的配位方式以及额外携带Lewis-碱性中心。CarPhoSCat项目分为两个分支：1)13族和14族配合物在Lewis酸和协同催化中的应用；2)具有催化活性的锰、铁和钴羰基配合物的开发及其在烯烃歧化反应中的应用。分支1开发了具有很强亲电性的双自由基类配体的阳离子络合物，因此与已有的Lewis酸相比，有望在氢化反应中表现出更好的性能。此外，这些阳离子络合物也是制备协同催化剂的有价值的起始原料。目标催化过程是烯烃的加氢以及胺和膦硼烷的脱氢聚合。在项目的后期阶段，从与合作催化剂的催化加氢反应中获得的见解将用于解决更具挑战性的转化，如氢羟化和使用氨的氢胺化。CarPhoSCat项目的第二个分支涉及双自由基类化合物的锰、铁和钴羰基配合物的合成。这些化合物是制备各种催化活性、低配位的贱金属配合物的很有前途的原料。重点将放在在烯烃歧化反应中活跃的亚烷基化合物上。强烈的金属-配体相互作用以及微调双自由基类化合物中的电子和空间性质的可能性将有利于这一项目。

Due to their environmental and economical implications, there is an ongoing interest to replace noble metals in homogeneous catalysis by their more earth-abundant 3d counterparts (base metals) or to mimic the behaviour of transition metals using main-group element compounds. For this purpose, the development of specialized ligand systems is necessary. Generally, these can be divided into two categories: redox-active ligands in which the ligand itself participates in electron-transfer processes, thus enabling the typical two-electron redox-steps associated with precious metal catalysts and ligands with strongly basic sites which assist in heterolytic cleavage of covalent bonds in the substrates (cooperative bond activation). Despite the many impressive achievements using these two concepts, homogeneous main-group and base metal catalysts are often inferior in terms of activity and selectivity in comparison with noble metal catalysts. The goal of the CarPhoSCat research project is to address and overcome some of the limitations by the development of main-group and base metal catalysts with carbene- and phosphine-substituted biradicaloid ligands. Such ligands feature strong metal-ligand interactions, support redox-activity, flexible coordination modes and additionally carry Lewis-basic sites. The CarPhoSCat project is divided into two branches: 1) The application of group 13 and 14 complexes in Lewis-acid and cooperative catalysis, and 2) the development of catalytically active manganese, iron and cobalt carbonyl complexes and their application in olefin metathesis. Branch 1 develops cationic complexes of biradicaloid ligands with a strong electrophilicity and are thus expected to show improved performance in hydroelementation reactions compared to established Lewis-acids. Furthermore, these cationic complexes are valuable starting materials to prepare cooperative catalysts. The targeted catalytic processes are the hydrogenation of olefins and the dehydropolymerization of amine and phosphine boranes. In later stages of the project, the insight gained from the catalytic hydrogenation reactions with the cooperative catalysts will be used to tackle even more challenging transformations such as hydrohydroxylations and hydroaminations using ammonia. Branch 2 of the CarPhoSCat project deals with the synthesis of manganese, iron and cobalt carbonyl complexes of biradicaloids. These compounds are promising starting materials for the preparation of various catalytically active, low-coordinate base metal complexes. The emphasis will be on alkylidene complexes which are active in olefin metathesis. The strong metal-ligand interactions and the possibility of fine tuning the electronic and steric properties within the biradicaloid complexes will be beneficial for this project.