In this Marie Sklodowska Curie Individual Fellowship titled “Ligand Design for Nitrogen Activation” (LiDeNiAc) a novel class of phosphaalkene-based ligands for the preparation of electron-rich vanadium and molybdenum complexes should be synthesized. The MSC Researach Fellow conducting this research was particularly interested in advancing pyridine-based ligands with two phosphaalkene sub-units. Phosphaalkenes are systems with a PC double bond and therefore possess the ability to accept electron-density from highly reduced metal centers. Highly reduced metal centers on the other hand are necessary to facilitate the coordination and activation of atmospheric dinitrogen.
The use of N2 as a resource is of fundamental importance for society, as it is abundant and can be deemed renewable. Even though the Haber-Bosch process uses dinitrogen and hydrogen to yield ammonia, it is energy and resource intensive, while also producing greenhouse gases. It is therefore desirable to develop processes in which nitrogen is directly integrated into value-added chemicals, such as amines, pyridines or amides, all of which are important base-chemicals (usually derived from ammonia).
In this MSC action novel PDPa ligands were successfully synthesized, however they were found to be particularly sensitive to hydrolysis (towards reacting with residual water), and therefore, the direction of project was adjusted after the completion of work package 1. In the first phase the introduction of commercially available starting materials for the ligand design was tested, and it was found that in these cases three-membered phosphorus ring systems, so-called triphosphiranes, form selectively. Additionally, one of the starting materials used for the synthesis of PDPa ligands turned out to be a valuable catalyst for the reaction of alkynes with anilines, a so-called hydroamination reaction. These reactions are used in organic synthesis and play an important role in the design of novel drugs. We developed a system that works at low catalyst loadings, therefore contributing to the improvement of these hydroamination reactions. Overall the MSC fellow has shown that the proposed PDPa ligands can be synthesized and investigations of their coordination chemistry are still on-going. In addition, the impact of the action was extended into the field of hydroamination reactions and the selective synthesis of triphosphiranes is expected to allow the design of phosphide materials, used for example for the desulfurization of crude oil.
Summary of the context and overall objectives of the project (For the final period, include the conclusions of the action)
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Ligand design should be used as a tool to develop transition metal complexes for the activation and functionalization of atmospheric nitrogen. Formal objectives of this MSC Action have been to (a) develop synthetic strategies towards a variety of pyridine-diphosphaalkene (PDPa) ligands, (b) to study their coordination chemistry and (c) to investigate the nitrogen-binding towards vanadium and molybdenum complexes with PDPa ligands. The use of dinitrogen as a resource is of fundamental importance for society, as it is abundant (ca. 79% of our atmosphere) and can consequently be deemed renewable. It is therefore desirable to develop processes in which nitrogen is directly integrated into value-added chemicals, such as amines, pyridines or amides, all of which are important base-chemicals. Another important goal of this MSC IF was to foster the development and growth of the experienced researcher, through active participation in teaching activities, organization of workshops and outreach activities. The goals and objectives of this MSCA have been partially met, however, an efficient risk management helped to give the project a new direction and to enhance the overall impact of the action. A novel, selective and high-yielding route towards triphosphiranes was developed. PDPa ligands could be synthesized and their potential for the coordination, activation and functionalization of atmospheric dinitrogen is still investigated.
