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.