Kinetics and Mechanism of the Platinum(II)‐Catalyzed Hydroarylation of Vinyl Arenes with 1,2‐Dimethylindole

The mechanism of the intermolecular hydroarylation of vinyl arenes (1) with 1,2‐dimethylindole (2) catalyzed by PtCl2 has been evaluated through a combination of kinetic analysis, deuterium labeling studies, and stereochemical analysis. The results of these and additional experiments are consistent with a mechanism for hydroarylation involving rapid and reversible complexation of vinyl arene to the catalytically inactive platinum mono(vinyl arene)complex trans‐PtCl2(H2C=CHAr)(solvent) to form the reactive platinum bis(vinyl arene) complex trans‐PtCl2(H2C=CHAr)2, which undergoes turnover‐limiting, outer‐sphere attack of indole. Rapid protodemetallation of the resulting platinum alkyl complex releases product and regenerates the equilibrating mixture of platinum π‐vinyl arene complexes.