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. Spectra of Al(acetone)(N) and ions with the stoichiometry of Al(acetone) ( = 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 ≥ 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 = 5, as evidenced by a new peak observed at 1185 cm characteristic of the pinacolate C-O stretch.