The homogeneous catalysis by gold(I) complexes generally acts in an alkyne as substrate and occurs under a nucleophilic addition, forming the anti alkene as the product. First, a pre-catalysis step with silver salts is done, acting on LAuCl specie (where L is an organic ligand), which generates LAu + catalyst when breaking Au-Cl bond. Recently, the hydrochlorination reaction of alkynes catalyzed by gold(I) complexes was reported, under room temperature and open air, without the pre-catalysis step and possibly maintaining the Au-Cl bond all over the reaction course. This could be feasible by hydrogen bonds between HCl, HFIP (hexafluoroisopropanol) molecules and the inactive catalyst, LAuCl. Later, a new study, using a bromoalkyne as substrate, showed to be possible the alkene obtainment as a syn product, but without the presence of gold catalyst (or any other one). So, the gold presence leads the regioselectivity of the hydrochlorination of alkynes, resulting only the anti product. With Density Functional Theory (DFT), the reaction pathways were studied, with gold (LAu + ) and without it, aiming to understand the main aspects that drive the regioselectivity in the alkynes hydrochlorination reaction. The activation of LAuCl catalyst was studied either. In the regioselectivity case, the steric hindrance promoted by bromine atom guides the major formation of syn product, which transition state is 3 kcal.mol -1 more stable than the anti one. In the gold reaction, the metal is the responsible one for steric hindrance to the nucleophile, directing it to the anti position. Finally, in the LAuCl catalyzed reaction, HFIP molecule seems to be decisive to initiate the catalyst activation, by its interaction with the triple bond.
