Both industrial and biochemical ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong triple bond of dinitrogen. Such multimetallic cooperation for dinitrogen cleavage is also the general rule for dinitrogen reductive cleavage with molecular systems and surfaces. We have observed cleavage of dinitrogen at 250°C and atmospheric pressure by dihydrogen on isolated silica surface–supported tantalum(III) and tantalum(V) hydride centers [(≡Si-O) ₂ Ta ^III -H] and [(≡Si-O) ₂ Ta ^V H ₃ ], leading to the Ta ^V amido imido product [(≡SiO) ₂ Ta(=NH)(NH ₂ )]: We assigned the product structure based on extensive characterization by infrared and solid-state nuclear magnetic resonance spectroscopy, isotopic labeling studies, and supporting data from x-ray absorption and theoretical simulations. Reaction intermediates revealed by in situ monitoring of the reaction with infrared spectroscopy support a mechanism highly distinct from those previously observed in enzymatic, organometallic, and heterogeneous N ₂ activating systems.