Thermal Activation of Ammonia by Transition-Metal Hydroxide Cations

With the exception of [Cu(OH)]⁺ , the thermal reactions of the first-row transition-metal hydroxide cations, [Sc(OH)]⁺ -[Zn(OH)]⁺ , with ammonia have been studied by means of gas-phase experiments and by computational methods for the whole series. The primary reaction channels involve NH bond activation, forming [M(NH₂ )]⁺ concomitantly with the elimination of water, and adduct formation, leading to [M(OH)(NH₃ )]⁺ . Furthermore, [Ti(OH)]⁺ and [V(OH)]⁺ react with ammonia under dehydrogenation conditions, leading to [M,O,N,H₂ ]⁺ (M=Ti, V), and for [Ni(OH)]⁺ ligand exchange is observed. Computations of the main reaction channels have been performed for the [M(OH)]⁺ /NH₃ couples (M=Sc-Zn) to uncover the underlying reaction mechanism and periodic trends across the first row. For NH bond activation, σ-bond metathesis was found to be the underlying mechanism.