Steric and Acidity Control in Hydrogen Bonding and Proton Transfer to <i>trans-</i>W(N₂)₂(dppe)₂

The interaction of <i>trans-</i>W­(N₂)₂(dppe)₂ (<b>1</b>; dppe = 1,2-bis­(diphenylphosphino)­ethane) with relatively weak acids (<i>p</i>-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