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 center dot center dot center dot H hydrogen bonds with single H2O 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 sigma-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.