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 la beling experiments in the gasphase and solution, and nb initio calcula tions is used to study the C-H activation reactions of [CpIr(PMe3)(CH 3)](+) and [CpIr(PMe3)(CH3)](+). The reaction in the gas phase was fou nd to proceed through a Cp or [CpIr(eta(2)-CH2-PMe2)](+) intermediate . Quantitative collision-induced dissociation (CID) threshold measurem ents were used along with general models for ion-molecule reactions to construct potential energy diagrams which rationalize the gasphase re sults. The comparison between the two complexes, and between the react ions in the gas phase and in solution, suggests that the reaction thro ugh the intermediacy of a metallaphosphacyclopropane could be favored over the conventional (and simpler) oxidative addition/reductive elimi nation mechanism when the Ir(III) complex is rendered more electron de ficient.