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

由于其对环境和经济的影响，人们一直对在均相催化中用地球上更丰富的三维对应物（贱金属）取代贵金属或使用主族元素化合物模拟过渡金属的行为感兴趣。为此，开发专门的配体系统是必要的。一般来说，这些可以分为两类：一类是氧化还原活性配体，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双电子氧化还原步骤；另一类是具有强碱性位点的配体，有助于底物共价键的异裂裂解（协同键激活）。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以碳和膦取代的双根碱配体为主基和贱金属催化剂来解决和克服一些局限性。这些配体具有强的金属-配体相互作用，支持氧化还原活性，灵活的配位模式，另外还携带lewis碱基位点。CarPhoSCat项目分为两个分支：1)13和14族配合物在lewis -酸和协同催化中的应用，2)催化活性锰、铁和钴羰基配合物的开发及其在烯烃分解中的应用。分支1形成具有强亲电性的双二根酸配体的阳离子配合物，因此与已建立的路易斯酸相比，有望在氢元素反应中表现出更好的性能。此外，这些阳离子配合物是制备协同催化剂的重要起始材料。目标催化过程是烯烃的加氢反应和胺和磷硼烷的脱氢聚合反应。在项目的后期阶段，从与合作催化剂的催化氢化反应中获得的见解将用于解决更具挑战性的转化，例如使用氨的氢化和氢胺化。CarPhoSCat项目的分支2处理双根碱的锰、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贱金属配合物的有希望的起始材料。重点是在烯烃复分解中具有活性的烷基烯配合物。金属与配体之间的强相互作用以及对双根碱配合物的电子和空间性质进行微调的可能性将有利于本项目的开展。

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.