The resulting dissociation surfaces and barriers for Au(NHC) 2 BrAu -Br are shown in Figure . Also for this complex, we were interested in the association process. The association barrier for the dissociation of the Br -was estimated to be between 4.6 and 28.5 kJ mol -1 , depending on the choice of the γ cleave -value. For γ cleave = 0.1, no barrier has been found. By comparing the barriers for both complexes, we obtain 18 kJ mol -1 vs. 5 kJ mol -1 for the Pd-and the Au-complex, when assuming a γ cleave of 0.05. We see that this methodology captures our chemical intuition, where the bulky phosphine should have a higher barrier than the small Br -.