Cyclam Based Transition Metal Complexes and Their Performance in Established and New Application Areas

• Applicants: Professor Dr. Ulf-Peter Apfel; Professor Dr. Kallol Ray
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 383043091

Unraveling the mechanistic basis and operational principles of the activation of small molecules like dioxygen (O2), or carbon dioxide (CO2) represents a formidable challenge to the chemical sciences, and addressing these challenges is essential for the design and development of efficient catalysts. Since nature mostly uses metal ions to activate these relatively inert molecules and modulate their reactivity, much inspiration for the field has come from bioinorganic chemistry. Among the different utilized tetradentate and pentadentate ligand systems, tetraazamacrocyclic cyclams have proved to be versatile ligands in the biomimetic chemistry of O2 or CO2 activation via the corresponding metal complexes. In our continuous effort to uncover structure-reactivity relationships of biomimetic model complexes, in the previous funding period, we performed a directed alteration of the tetraazamacrocyclic framework by consecutive substitution of the nitrogen-donor atoms by oxygen, sulfur, phosphorous and selenium atoms to generate a library of heteroatom substituted macrocyclic ligand systems. The metal complexes of only a few of the synthesized ligands could be tested for their ability to perform O2/CO2 activation reactions. We showed that secondary interactions of the bound O2/CO2 with the ancillary ligands play a vital role in controlling the stability and reactivity of the transient intermediates formed upon O2/CO2 activations. These, in turn, exerted significant influence on the product selectivity and the overpotential of the (electro)catalytic CO2/O2 reduction reactions. Building on our results from the previously granted DFG-proposal, we intend to continue our ongoing intensive and successful collaborative studies on the mechanistic investigation of the transition metal-mediated CO2/O2 reductions, paying particular emphasis to the coordination and catalytic properties of the yet unexplored ligand systems, and to the detailed spectroscopic characterization of some of the novel reactive intermediates generated in the first funding period. The main aim is to understand the prevailing mechanisms of small molecule activation in more detail, with the aim of exploring the potential of many of the synthesized complexes in a wide range of new application areas. This study may allow vital insights into the prerequisites necessary for the design of efficient catalysts for the selective functionalization of unactivated C–H bonds, O2 reduction, or CO2/H+ activations by using cheap and readily available first-row transition metals under ambient conditions.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partner: Professor Dr. Nicolai Lehnert