Ammonia Activation, H₂ Evolution and Nitride Formation from a Molybdenum Complex with a Chemically and Redox Noninnocent Ligand

Treatment of the bis(imino)pyridine molybdenum η⁶-benzene complex (^iPrPDI)Mo(η⁶-C₆H₆) (^iPrPDI, 2,6-(2,6-iPr₂C₆H₃NCMe)₂C₅H₃N) with NH₃ resulted in coordination induced haptotropic rearrangement of the arene to form (^iPrPDI)Mo(NH₃)₂(η²-C₆H₆). Analogous η²-ethylene and η²-cyclohexene complexes were also synthesized, and the latter was crystallographically characterized. All three compounds undergo loss of the η²-coordinated ligand followed by N-H bond activation, bis(imino)pyridine modification, and H₂ loss. A dual ammonia activation approach has been discovered whereby reversible M-L cooperativity and coordination induced bond weakening likely contribute to dihydrogen formation. Significantly, the weakened N-H bonds in (^iPrPDI)Mo(NH₃)₂(η²-C₂H₄) enabled hydrogen atom abstraction and synthesis of a terminal nitride from coordinated ammonia, a key step in NH₃ oxidation.