Reactions of Indene and Indoles with Platinum Methyl Cations: Indene C-H Activation, Indole π vs. Nitrogen Lone-Pair Coordination

Reactions of indene and various substituted indoles with [(diimine)Pt(II)(Me)(TFE)](+) cations have been studied (diimine = ArN = C(Me) - C(Me) = NAr; TFE = 2,2,2-trifluoroethanol). Indene displaces the TFE ligand from platinum to form a stable π coordination complex that, upon heating, undergoes C-H activation with first order kinetics, ΔH(‡) = 29 kcal/mol, ΔS(‡) = 10 eu, and a kinetic isotope effect of 1.1 at 60 °C. Indoles also initially form coordination complexes through the C2=C3 olefin, but these undergo rearrangement to the corresponding N-bound complexes. The relative rates of initial coordination and rearrangement are affected by excess acid or methyl substitution on indole.