Dehydration of Alkanones by Bare FeO+ Involves the ω/(ω-1) Positions: Exclusion of Iron Carbenes as Intermediates

Article abstract of DOI:10.1002/hlca.19900730217

Fourier-transform ion-cyclotron-resonance (FTICR) mass spectrometry has been used to uncover the mechanisms by which FeO+ dehydrates heptan-4-one (5a) and nonan-5-one (6a)in the gas phase.The study of isotopomeric ketones provides evidence that H2O loss is not due to a 1,1-elimination, thus ruling out the intermediacy of high-valent iron-carbene species.Rather, H2O is generated in a formal 1,2-elimination involving the ω/ω-1 positions of the alkyl chain ( remote C-H bond activation ).In the consecutive alkene/H2O elimination, the olefins (ethylene from 5a and propene from 6a) originate from the terminal part of one alkyl chain, and the H-atom is transferred to the FeO+ moiety in the course of this process, builds up together with an H-atom from the ω/ω-1 position of the other alkyl chain the H2O molecule.In either case, the O-atom of H2O is provided by the FeO+ species.