Gas-phase reactions of iron(1+) with ketones and ethers

Abstract

A pulsed laser has been used in conjunction with an ion cyclotron resonance spectrometer to generate and study the gas-phase ion-molecule reactions of Fe+ with simple carbonyl compounds and ethers. Oxidative addition reactions are observed, producing alkyl, acyl, and alkoxide intermediates which undergo intramolecular rearrangement by a 8-hydride shift mechanism. Decarbonylation reactions are observed with only a few small ketones. The main reaction channel is dehydrogenation for unbranched ketones and reductive elimination of methane for those branched at the (Y carbon. Reactions of Fe' with diisopropyl ketone, cyclohexanone, cyclopentanone, and tetrahydrofuran suggest the existence of intermediate and stable ?r-allyl complexes resulting from sequential @-hydride shifts.T o a solution chemist the direct cleavage of carbon-carbon bonds by transition metals is not as common a process as carbon-carbon bond formation. T o the gas-phase ion-molecule chemist, however, carbon+arbon bond cleavage by atomic metal ions and metal-ion complexes may be a more common occurrence.

An experimental study of the mechanism for the combined CO and CH bond activation of dimethylether by bare Fe+ ions

“…In full accordance with the ion-cyclotron-resonance studies of Freiser and coworkers [6], loss of CH 4 largely prevails in the metastable ion spectrum of the complex 1 generated by chemical ionization of Fe(CO) 5 with dimethylether. Upon collisional activation, several other fragments are formed, among which loss of the entire ligand to form bare Fe + is most prominent; nevertheless, elimination of methane does still give rise to the base peak in the CA spectrum.…”

“…Already in 1981, Freiser and coworkers [6] noted that bare Fe + can activate dimethylether to afford the formaldehyde/Fe + complex as ionic and methane as neutral product (reaction (1)) [7,8]:…”

Theoretical Investigation of the Decarbonylation of Acetaldehyde by Fe+ and Cr+

“…Decarbonylation of aldehydes in solution [16,17] and on solid surfaces [18] has been extensively studied. Gas-phase decarbonylation of aldehydes and ketones by CpNi + (Cp h 5 -C 5 H 5 ), as well as the bare Fe + and Co + cations, has been demonstrated in ICR experiments by Beauchamp and co-workers [19,20] and Freiser and co-workers, [21] and ion-beam experiments by Beauchamp and co-workers. [22] These investigations indicate that decarbonylation of acetaldehyde by transition metal ions is a dominant channel at low reaction energies, and the oxidative addition of metal ions across the CÀC and/or aldehyde CÀH bonds occurs.…”

Coupling reactions of Fe(benzyne)+ and Fe(naphthyne)+ in the gas phase

“…Fe`was generated by laser desorption of a pure iron metal target using a Quanta-Ray Nd : YAG laser operated at its fundamental IR output (1064 mm). 26 Argon at a pressure of about 5.0 ] 10~6 Torr was used as the collision gas for thermalization and collision-induced dissociation (CID)27 experiments. Standard FT-ICR ion ejection techniques28 and SWIFT excitation29 were used to study ionÈmolecule reaction pathways and to isolate an ion prior to CID experiments.…”