A Combined Gas-Phase, Solution-Phase, and Computational Study of C−H Activation by Cationic Iridium(III) Complexes

A combination of electrospray ionization MS/MS techniques, isotopic labeling experiments in the gas-phase and solution, and ab initio calculations is used to study the C−H activation reactions of [Cp*Ir(PMe 3 )(CH 3 )] + and [CpIr(PMe 3 )(CH 3 )] + . The reaction in the gas phase was found to proceed through a Cp or [Cp*Ir(η 2 -CH 2 PMe 2 )] + intermediate. Quantitative collision-induced dissociation (CID) threshold measurements were used along with general models for ion−molecule reactions to construct potential energy diagrams which rationalize the gas-phase results. The comparison between the two complexes, and between the reactions in the gas phase and in solution, suggests that the reaction through the intermediacy of a metallaphosphacyclopropane could be favored over the conventional (and simpler) oxidative addition/reductive elimination mechanism when the Ir(III) complex is rendered more electron deficient.