Comparative gas-phase and sollution-phase investigations of the mechanism of C-H activation by [(N-N)Pt(CH3)(L)]+

Contrary to previous claims in the literature, there is no solvent assistence by 2,2,2-trifluoroethanol (TFE) in C-H activation reactions by cationic Pt(II) complexes. Both electrospray ionization tandem mass spectrometric studies of isolated gas-phase intermediates and solution-phase kinetic spectroscopy indicate that TFE serves only as an inert diluent. TFE was found, in the gas-phase experiment to provide no acceleration of the loss of methane or benzene from preselected [(N-N)Pt(CH3)(C6H6)](+) or [(N-N)Pt(CH4)(C6H5)](+) ions. In solution, the overall C-H activation reaction of benzene by [(N-N)Pt(CH3)(H2O)]+BF4- was found to be zero-order in TFE. While it is on one hand disappointing that the claimed facilitation of C-H activation by solvent assistance by TFE at the rate-determining transition state is not supported by the present experimental data, it is on the other hand encouraging that extremely rapid C-H activation (on the time scale of seconds at room temperature) in solution may be achieved in ordinary solvents as long as the solvent is not strongly coordinating.