Steric and Acidity Control in Hydrogen Bonding and Proton Transfer to trans-W(N)(dppe).

The interaction of trans-W(N)(dppe) (1; dppe = 1,2-bis(diphenylphosphino)ethane) with relatively weak acids (p-nitrophenol, fluorinated alcohols, CFCOOH) 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 N to NH-can be avoided by using weaker and, more importantly, bulkier acids.