Computational design of cooperatively acting molecular catalyst systems: carbene based tungsten- or molybdenum-catalysts with rhodium- or iridium-complexes for the ionic hydrogenation of N 2 to NH 3 .

This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N 2 with H 2 , leading to NH 3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M 1 (H) 2 ] (M 1 = W/Mo) were chosen to bind N 2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M 2 {2-(2-pyridyl)phenyl}(CH 3 CN)] + (Cp* = C 5 (CH 3 ) 5 and M 2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H 2 splitting. The stepwise transfer of protons and hydrides to the bound N 2 and intermediate N x H y units results in the formation of NH 3 . Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol -1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol -1 demonstrating significant potential for molecular catalysts for the N 2 /H 2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected.