We report an experimental and computational analysis of the effects of hydrogen bonding to a metal dinitrogen complex. A series of H-bond donors over a wide pK(a) range (Delta 20) interact with the nitrogen unit of a Re-I-(N-2) complex at room temperature. Analysis by N-15 NMR, IR spectroscopy, association equilibria, and DFT studies indicates that the H-bonding interaction polarizes and weakens the N-N bond. These results provide insight into the role of the secondary sphere residues in nitrogenase enzymes.