Predicting Selectivity in Oxidative Addition of C-S Bonds of Substituted Thiophenes to a Platinum(0) Fragment: An Experimental and Theoretical Study

Exchange reactions of 2- and 3-cyanothiophene, 2- and 3-methylthiophene, and 2- and 3-methoxythiophene, either with thiophene in the thiaplatinacycle Pt(dippe) (kappa(2)-C,S-C4H4S) or with norbornene in Pt(dippe)(nor)(2), were performed to probe the kinetic and thermodynamic selectivity of the C-S bond activation reactions. Kinetic data were collected by following these reactions by P-31{H-1} NMR spectroscopy. The ground-state energies of the two possible products and the transition-state energies leading to the formation of these products were calculated using density functional theory. The comparison of the predicted selectivities from calculations with the experimentally observed selectivities showed good agreement for thermodynamic selectivity, but only moderate agreement for kinetic selectivity. The reactions with 2-cyanothiophene, 3-cyanothiophene, and 3-methoxythiophene gave kinetic products that were less favored thermodynamically. All of the other substituted thiophenes gave kinetic products that were also preferred thermodynamically. These results indicate that the selectivities seen in the C-S bond activation reactions of substituted thiophenes with the [Pt(dippe)] fragment are initially under kinetic control.