Environmentally Benign Manganese Catalyzed Reactions

Driven by both public demand and government regulations, pharmaceutical and fine chemical manufacturers are increasingly seeking to replace stoichiometric reagents as well as precious metal based catalysts used in synthetic transformations in order to develop greener, safer, and more cost- effective chemical processes. A process we are interested in is the catalytic hydrogenation of multiple bonds via molecular hydrogen. This plays a significant role in modern synthetic organic chemistry and is excellently performed by many transition metal complexes containing noble metals such as ruthenium, rhodium, or iridium. The limited availability of precious metals, their high price, and their toxicity diminish their attractiveness in the long run and more economical and environmentally friendly alternatives have to be found which are in line with green chemistry guidelines. This project aims at the discovery, development, and implementation of new catalytic methodologies based on manganese catalysts which may open the door to the sustainable production of pharmaceuticals and fine chemicals (Sustainability through Base Metal Catalysis). In this respect, the preparation of well-defined manganese-based catalysts of comparable or even higher activity is desirable. Manganese is the third most abundant transition metal in the earth crust, ubiquitously available, and non-toxic. In sum it is expected to generate fundamental understanding of new concepts in bond activation and may lead to efficient manganese and base metal catalysis in general of reactions formerly restricted to noble metals and result in the development of new, environmentally benign catalytic processes.

In sum, this project generated a fundamental understanding of new concepts in the area Sustainability through Base Metal Catalysis. This led to the development of efficient manganese-based catalysis in reactions formerly restricted to noble metals, and resulted in the development of new, environmentally benign catalytic processes. Driven by both public demand and government regulations, pharmaceutical and fine chemical manufacturers are increasingly seeking to replace stoichiometric reagents as well as precious metal-based catalysts. These modifications used in synthetic transformations will develop greener, safer, and more cost-effective chemical processes. A process we were interested in was and still is the catalytic hydrogenation and dehydrogenation reactions involving molecular hydrogen and alcohols, respectively. This plays a significant role in modern synthetic organic chemistry for the production of pharmaceuticals and is excellently performed by many transition metal complexes containing noble metals such as ruthenium, rhodium, or iridium. The limited availability of precious metals, their high cost, and their toxicity diminish their attractiveness in the long run and more economical and environmentally friendly alternatives have to be found which are in line with green chemistry guidelines. This project aimed at the discovery, development, and implementation of new catalytic methodologies based on manganese catalysts which open the door to the sustainable production of pharmaceuticals and fine chemicals (Sustainability through Base Metal Catalysis). In the course of this project, we were able to develop well-defined manganese-based catalysts for the hydrogenation of aldehydes and ketones to alcohols, the hydrogenation of nitriles, carbon dioxide and alkenes as well as aminomethylation of aromatic compounds with methanol as C1 building and the hydroboration of carbon dioxide, respectively. In addition, we also started to develop related chemistry with other base metals such as cobalt and metals such as rhenium. The outcome of this project is documented in 20 publications in highly ranked peer-reviewed journals.