Tipping the Balance between Ligand and Metal Protonation due to Relativistic Effects: Unusually High Proton Affinity in Gold(I) Pincer Complexes.

Quantum theoretical studies show that the extremely high proton affinity at the metal center of the unusual T-shaped (LXL)AuI -pincer complex, consisting of a carbazole framework and two mesoionic carbenes, is caused by relativistic effects. This brings the basicity of the AuI center in line with the electron-rich nitrogen atom of the carbazole ring system, resulting in one of the highest proton affinities for a neutral molecule.