Water Serving as Cocatalyst for the Highly Efficient Homogeneously Catalyzed Conversion of N ₂ O/H ₂ Mixtures with Optimized Rhodium NHC Complexes

Abstract

Abstract Nitrous oxide (N 2 O) is a valuable oxygen/nitrogen transfer reagent but reactions with N 2 O are challenging due to its inertness. Consequently, it accumulates in the atmosphere, and because it is both an ozone‐depleting reagent and potent green‐house gas, effective mitigation methods become important. This study presents rhodium(I) amido bis(olefin) N ‐heterocyclic carbene complexes [Rh(trop 2 N)(NHC)] as robust homogeneous catalysts for the direct hydrogenation of N 2 O. Kinetic experiments and DFT calculations show that increasing π ‐acidity of the NHC and the presence of water significantly enhance the catalytic efficiency. The rhodium‐amido bond facilitates cooperative H 2 ‐cleavage and oxygen atom transfer from N 2 O. The catalyst is regenerated with the loss of water from the hydroxide intermediate [Rh(OH)(trop 2 NH)(NHC)], which forms a dimeric complex with a central bridging hydrated hydroxide ligand [H 3 O 2 ] − . Water facilitates dinitrogen (N 2 ) loss from an intermediate containing an oxy‐diazene ligand [H─N═N─O] − . The optimized catalyst achieves a TON > 230 000 and TOF > 1300 h −1 .