Research Projects

The synthesis of ammonia (NH₃) from dinitrogen (N₂) is a critical chemical process commonly achieved biologically by nitrogenase enzymes and industrially via the Haber-Bosch process. While the industrial Haber-Bosch process can fulfill the current NH₃ requirement, its extremely high energy demand and subsequent massive carbon footprint prompted continuous research for sustainable alternatives for converting N₂ to NH₃. Additionally, NH₃ has been considered as an alternative to hydrogen (H₂) for fuel and energy storage material. This has recently opened up a new research area to find suitable catalytic systems that selectively and efficiently oxidize NH₃ to N₂. While metalloenzymes employ their multimetallic active sites to activate small molecules under ambient conditions, so far homogeneous N₂ fixation and NH₃ oxidation have mainly been done with either a single metal center or with homobimetallic catalysts, which often makes these process relatively inefficient. Although natural enzymes often exploit the secondary coordination sphere effect to facilitate small molecule activation under ambient conditions, the same concept has not been properly utilized for chemical N₂ fixation and NH₃ oxidation. Inspired by the biological nitrogen fixation, where N₂ is activated and functionalized through the intramolecular cooperative effect of Fe₇Mo cofactor, and the secondary coordination sphere effect of the histidine residue present in the nitrogenase enzymes, our target is to develop the dinucleating ligand systems that can inherently form bimetallic complexes and contain linker with additional binding sites that can exhibit secondary coordination sphere effect. In this regard, we will focus on developing novel homogeneous catalytic systems based on 3d-transition metals (e.g. Fe, Co, Cu, etc.). To achieve this, we plan to synthesize a series of bis(β-diketiminate) ligands with a linker having additional coordination sites that will help to stabilize the probable intermediates like the transition metal complexes of [N=N]²-, [N-N]⁴-, N³-, [HN=NH], [H₂N-NH₂] and NH₃ ligands involved in the N₂ reduction and NH₃ oxidation cycles through secondary coordination sphere effect. Along with linkers, the proposed ligands will have additional sites that can be varied to tune the steric and electronic profiles of the catalysts. These proposed metal complexes will exploit the bimetallic and the secondary coordination sphere effects to reduce N₂ to NH₃ and oxidize NH₃ to N₂ under ambient conditions. The bimetallic catalysts will be able to reduce N₂ or oxidize NH₃ via an expected more facile intramolecular pathway over the intermolecular pathway commonly observed with monometallic catalysts. In summary, this project will focus on new bis(β-diketiminate) ligand coordinated bimetallic catalysts synthesis, their characterization, and catalytic studies to understand the mechanisms driving the N₂ fixation and NH₃ oxidation.