Al + Activates Acetone to Form Pinacolate.

The interaction between aluminum cations and acetone is studied in the gas phase via photodissociation vibrational spectroscopy from 1100 to 2000 cm -1 . Spectra of Al + (acetone)(N 2 ) and ions with the stoichiometry of Al + (acetone) n ( n = 2-5) were measured. The experimental results are compared to DFT calculated vibrational spectra to determine the structures of the complexes. The spectra show a red shift of the C=O stretch and a blue shift of the CCC stretch, which decrease as the size of the clusters increases. The calculations predict that the most stable isomer for n ≥ 3 is a pinacolate, in which oxidation of the Al + enables reductive C-C coupling between two acetone ligands. Experimentally, pinacolate formation is observed for n = 5, as evidenced by a new peak observed at 1185 cm -1 characteristic of the pinacolate C-O stretch.