Аннотация:The interaction of trans-W(N2)2(dppe)2 (1; dppe = 1,2-bis(diphenylphosphino)ethane) with relatively weak acids (p-nitrophenol, fluorinated alcohols, CF3COOH) was studied by means of variable temperature IR and NMR spectroscopy and complemented by DFT/B3PW91-D3 calculations. The results show, for the first time, the formation of a hydrogen bond to the coordinated dinitrogen, W–N≡N···H–O, that is preferred over H-bonding to the metal atom, W···H–O, despite the higher proton affinity of the latter. Protonation of the core metal—the undesirable side step in the conversion of N2 to NH3—can be avoided by using weaker and, more importantly, bulkier acids.