Catalytic NH3 Synthesis using N2/H2 at Molecular Transition Metal Complexes: Concepts for Lead Structure Determination using Computational Chemistry

While industrial NH3 synthesis based on the Haber-Bosch-process was invented more than a century ago, there is still no molecular catalyst available which reduces N-2 in the reaction system N-2/H-2 to NH3. As the many efforts of experimentally working research groups to develop a molecular catalyst for NH3 synthesis from N-2/H-2 have led to a variety of stoichiometric reductions it seems justified to undertake the attempt of systematizing the various approaches of how the N-2 molecule might be reduced to NH3 with H-2 at a transition metal complex. In this contribution therefore a variety of intuition-based concepts are presented with the intention to show how the problem can be approached. While no claim for completeness is made, these concepts intend to generate a working plan for future research. Beyond this, it is suggested that these concepts should be evaluated with regard to experimental feasibility by checking barrier heights of single reaction steps and also by computation of whole catalytic cycles employing density functional theory (DFT) calculations. This serves as a tool which extends the empirically driven search process and expands it by computed insights which can be used to rationalize the various challenges which must be met.