| Project Detail |
The utilization of base metals, that is, Earth-abundant first-row transition metals, in homogeneous catalysis has witnessed significant developments over the last years, and in particular in cross-coupling and reductive transformations, processes have been developed that do not rely on precious metals anymore. In fact, some processes are even complementary and provide new strategies for the synthesis of added-value products. In contrast, homogeneous oxidation catalysis has been much less progressed, in parts because mechanistic concepts of oxidation catalysis are much less understood, and in other parts certainly also by the difficulties associated with controlling the ligand environment in high-valent base metal complexes. The lack of progress has severely limited the development of sustainable methods that reduce or avoid the use of rare and economically and environmentally unfriendly precious metals. Such methods are urgently needed, however, as many oxidation processes are bulk operations, either for the valorization of simple hydrocarbon feedstocks, or for energy-related processes such as water splitting or dehydrogenations to implement a hydrogen economy that does not rely on hydrocarbon resources.In this project, we aim at developing approaches towards efficient and sustainable oxidation catalysts. For this endeavor, we build on our expertise in developing custom-tailored ligand scaffolds for specific catalytic purposes. In particular, we have implemented donor-flexible ligands that are highly suitable for stabilizing the metal center in different oxidation states, and we have implemented these properties for the generation of catalysts with ultra-high activity, for example in olefin oxidation and hydrogen transfer reactions. Here, we aim specifically to-expand catalytic C-H amination to valorize simple substrates in an efficient and sustainable manner-boost formic acid dehydrogenation to provide tools for eco-friendly production of hydrogen as an environmentally benign fuel-explore the suitability of these catalyst families in other oxidations, including also the (electro)chemical oxidation of waterFor this purpose, we have identified specific classes of donor-flexible ligands that have the potential to support the metal center during catalytic transformations. In addition to triazolylidenes, we will exploit pyridylidene amines that are appropriately functionalized for chelation to support the metal-nitrogen bond during catalysis, and which are readily customizable by appropriate substituent incorporation. Moreover, we will explore N-heterocyclic boryl (NHB) ligands, a homologue of the widely used N-heterocyclic carbenes (NHCs). In contrast to NHCs, NHB ligands can be purpose-shaped through reversible interactions of Lewis bases with the boron center, which entails an unprecedented flexibility that is expected to have a significant impact on oxidation catalysis.We expect that this project will result in several catalytic systems with unparalleled activity for oxidative transformations that will be highly attractive for practitioners both in academia and industry. Probably even more relevant will be the general principles for ligand design that will emerge from this project, which we expect to be applicable for a range of other oxidative transformations. |
