Thesis defended December 16, 2025

Abstract
This work explores the potential of heptazine derivatives as building blocks for the design of new molecular homogeneous electrocatalysts for CO₂ reduction reaction (eCO2RR). Four bidentate heptazine-based ligands (Hept-Py, Hept-NHPy, Hept-Pz, and Hept-SH) were synthesized through original functionalization strategies and subsequently coordinated to various transition metals including Re(I), Mn(I), Co(II), and Co(III). All ligands and resulting mononuclear complexes were characterized using physicochemical methods and theoretical calculations to deepen the understanding of heptazine coordination chemistry. The heptazine core was found to strongly influence the electronic (optical and electrochemical) properties of these systems, particularly by modulating the energy and nature of the LUMO orbitals. The rhenium complexes were investigated as electrocatalysts for eCO2RR and displayed promising activity, modulated by the nature of the ligand and the proton source, although Faradaic efficiencies (FE) remain modest. The complex [Re(Hept-NHPy)(CO)3Br] achieved a FECO of 39%. These results highlight the potential of heptazine ligands as tunable platforms for molecular CO₂ electrocatalysis, while emphasizing the need to further optimize their electronic environment and stability to design more selective and efficient systems.