Mechanistic Insights into the Catalytic Acetylene Hydrochlorination over Pt(II) Chloro Complexes

Despite the Minamata Convention’s efforts to reduce mercury in industry, acetylene hydrochlorination still relies on a highly toxic HgCl2 catalyst, forcing the search for environmentally benign catalysts. The targeted development of new catalytic systems is hampered by the lack of well-defined concepts about the mechanism of the heterogeneously catalyzed reaction. Herein, density functional modeling of the energy profile for catalytic acetylene hydrochlorination over mechanically preactivated K2PtCl4 salt was correlated with experimental data, confirming the concept of “noninnocent/cooperative” ligands. Chloroplatination of π-coordinated acetylene by the HCl molecule to form the β-chlorovinyl PtII derivative is shown to be the rate-limiting step. It involves the attack by the Cl atom of the HCl molecule on the C atom of the π-complex to form the product of exclusively trans(anti)-addition across the triple bond, in agreement with the experiment. The neighboring platinum complex facilitates this conversion by donating a chloride ligand to bind the released H+ to form a new HCl molecule. In addition, the HCl/DCl kinetic isotope effect (KIE) estimated from the calculations is 3.1, close to KIE = 3.7 determined experimentally. These results establish a mechanistic understanding of the acetylene hydrochlorination over K2PtCl4 and highlight the involvement of two Pt-cites in catalyzing the reaction.