Preparing Gold(I) for Interactions with Proton Donors: The Elusive [Au]⋅⋅⋅HO Hydrogen Bond

MP2 and DFT calculations with correlation consistent basis sets indicate that isolated linear anionic dialkylgold(I) complexes form moderately strong (ca. 10 kcal mol(-1) ) Au⋅⋅⋅H hydrogen bonds with single H2 O molecules as donors in the absence of sterically demanding substituents. Relativistic effects are critically important in the attraction. Such bonds are significantly weaker in neutral, strong σ-donor N-heterocyclic carbene (NHC) complexes (ca. 5 kcal mol(-1) ). The overall association (>11 kcal mol(-1) ), however, is strengthened by co-operative, synergistic classical hydrogen bonding when the NHC ligands bear NH units. Further manipulation of the interaction by ligands positioned trans to the carbene, is possible.