The project aimed to achieve the following scientific and training objectives:
1.1.1 Scientific Objectives:
1. Synthesis of Ae-imido complexes (Ae=NR):
This part of the study aimed to isolate monomeric, or at most dimeric, Ae metal-imido complexes which are expected to show interesting reactivity. Three synthetic approaches were followed: i) deprotonation of amide (L-Mg-NH2) ii) reduction of L-Mg-N-NHC complexes; where L is BDI (β-diketiminate) ligand and NHC is N-heterocyclic carbene, and iii) desilylation of L-Mg-N(SiMe3)2. While it was very challenging to achieve syntheses of Ae=NH complexes, our results show generation of a few new Ae complexes that may be useful for further future research in this context. The goal of this objective is partially achieved by successful syntheses and reactivity investigations on iminato complexes of Mg. This work is currently in its final stage and a manuscript will soon be published.
2. Synthesis of Ae-nitrido complexes (Ae≡N):
The herein proposed nitrido complexes of the Ae metals may be obtained by 2e-reduction of Ae complexes with the azide anion: N3ˉ → N3ˉ + N2. The starting material L-Mg-N3 has been successfully synthesized from its corresponding iodide precursor. Crystal structure determination showed that the synthesized compound exists as a trimer. The L-Mg-N3 complex was subjected to reduction using K/KI and KC8. Reduction with KC8 lead to the formation of multiple products which posed problems in separation of new complexes. The goals of this objective were partially fulfilled, the detailed results are described in section 1.2.
3. Nitreones as positively charged Lewis bases and N-transfer reagent: The goal of this objective was to explore the chemistry of nitreones, which are N+ cations stabilized by NHC coordination with low-valent Mg complexes, i.e. {[(DiPePBDI*)Mg−][Na+]}2, where DiPePBDI* is β-diketiminate ligand (DiPePBDI*=CH{(CtBu)(2,6-Et2CHC6H3N)}2). Nitreones with various substitutions and low-valent Mg complexes were successfully synthesized using the reported method. Reaction between both compounds was challenging owing to the stability and solubility issues. However, this problem was overcome by the use of solid-state ball-milling. Unfortunately, this led to the formation of multiple products with highly complex NMR spectra. Also variation of educt ratio, ball-size, milling frequency did not result in selective reactivity. The details are shown in Section 1.2.
4. Theoretical studies using DFT method:
With the aim of better understanding the Ae-N bond in Ae=NR or Ae≡N complexes, this objective has been fully achieved. All experimental results were parallel studied by DFT calculations. DFT and bond analysis programs (NBO, AIM) methods were employed to evaluate these unique bond properties. For the heavier metals Ca, Sr and Ba, the relevance of d-orbitals was considered. Additionally, DFT methods were found to be highly useful to predict and understand potential energy surface of the unusual reactivity of the synthesized compounds and found to be highly useful in understanding catalytic cycles.
1.1.2 Training objectives
Scientific Training
Advanced skills of organometallic chemistry techniques:
This project allowed me to advance my basic knowledge of vacuum line techniques to a top level. I thoroughly explored chemistry practices using Schlenk-lines, Schlenk-centrifuges, cannula-transfer, high-pressure reactors, gas transfer techniques, inert gas boxes and a large variety of specially designed apparatus for the syntheses and handling of extremely air-sensitive, pyrophoric and temperature-labile compounds, in particular, for main group chemistry of group 2 metals. These skills were achieved during the synthesis of complexes outlined in WP1-WP3. Acquiring these technical skills extended my expertise to a new dimension of organometallic chemistry which will strongly benefit my professional career.
Advanced experience in theoretical calculations: My previous knowledge in theoretical chemistry has been extended with bond analysis techniques that are established in the HARDER group. My expertise in computational calculations using DFT methods has been tremendously expanded horizontally in the field of organometallic chemistry. Most of the experimental data generated was supported with detailed mechanistic insights from ab initio calculations, resulting in quality data for publications in high impact journals. This includes analysis of newly designed complexes with AIM, NBO or EDA-NOCV, extensive calculations on catalytic cycles including determination of transition states and intermediate energies. This part of the training was performed in WP4 using state-of-the-art software packages and high-end computer systems available in the HARDER group with constant support of Computer Chemistry Centre (CCC) FAU, Erlangen-Nuremberg.
Expertise in synthesis, reactivity and catalysis studies of low-valent Ae metal complexes:
The current project provided me significant exposure to the challenging synthesis, isolation and handling of low-valent main group metal complexes particularly involving Mg. These complexes were needed as precursors for the design of Ae-imido and Ae-nitrido compounds. The training also involved synthesis of some previously reported reagents using a variety of reducing agents. Part of training was also directed to gain experience in the catalytic applications of the synthesized compounds with a special focus on small molecule activation and homogeneous catalysis (for example hydrosilylation and hydrogenation reactions). My training also involved handling of an advanced high-pressure set-up for various gases. All the components of this training have been accomplished by performing the research work outlined in WP1-WP3.
Characterization techniques: With the support and guidance of Dr. Christian Färber (Academic Scientist, Harder group) I gained during my research work substantial knowledge in operating advanced NMR spectrometers. I also explored solid-state structure analysis using X-Ray diffractometry (XRD) in close guidance with Dr. Jens Langer (Academic Scientist, Harder group). This part of training was achieved under WP1-WP3.
Horizontal and key transferrable skills
During my training, I actively engaged in scientific knowledge transfer, demonstrating key horizontal skills in mentorship, collaboration, and leadership. As part of my professional development, I mentored undergraduate students, guiding them in research methodologies. Moreover, I also supported graduate students that wanted to learn the basics of theoretical calculations. This role strengthened my ability to communicate complex concepts effectively, a critical skill for both academia and industry.
Additionally, I leveraged my industrial experience to provide practical insights to the research group, bridging the gap between theoretical and applied chemistry. This experience not only reinforced my technical expertise but also enhanced my project management, teamwork, and training capabilities—essential transferable skills for future leadership roles in research and innovation.
