IR spectroscopic characterization of intermediates in a gas-phase ionic reaction: The decarbonylation of Co+(acetophenone)

Decarbonylation of acetophenone is a facile process mediated by Co+ complexation. Structures of two species on the gas-phase reaction path have been characterized by their infrared photodissociation spectroscopy, namely the Co+(acetophenone) complex itself, and the decarbonylated but still complexed product ion Co+(C7H8). Infrared spectra over the 500-1800 cm−1 frequency range were obtained by wavelength-dependent multiple-photon dissociation using the FELIX free electron laser and a Fourier-transform ion cyclotron resonance mass spectrometer. Structural characterizations were made by comparison with predicted spectra calculated by density functional theory (DFT) using the B3LYP functional. The initial complex Co+(acetophenone) was found to be intact, with little or no presence of rearrangement or bond-inserted structures. The spectrum indicates a mixture of O-bound and ring-bound isomers of this complex. The decarbonylated product ion was assigned to have the most stable structure, namely Co+(toluene), with no indication of the presence of possible bond-inserted isomers having a two-coordinate metal ion. A decarbonylation path involving metal ion insertion adjacent to the carbonyl group was suggested, and the corresponding bond-inserted complexes were computed to be energetically reasonable intermediate structures on the reaction path.