Reactions of FeCH3+ and CoCH3+ with Aliphatic Alkenes and Alkynes in the Gas Phase

Article abstract of DOI:10.1021/ja00307a008

The gas-phase reactions of FeCH3⁺ and CoCH3⁺ with a variety of alkenes are described by using Fourier transform mass spectrometry (FTMS).FeCH3⁺ is unreactive with ethene, while CoCH3⁺ reacts with ethene to yield the allyl product CoC3H5³.This reaction presumably proceeds by initial methyl migratory insertion into coordinated ethene to form a Co(propyl)⁺ complex which subsequently dehydrogenates.Reactions with alkenes containing labile hydrogens α to the double bond proceed by initial elimination of methane to form an activated ?-allyl complex which may subsequently decompose further.Both FeCH3⁺ and CoCH3⁺ undergo migratory insertion into coordinated butadiene generating a ?-pentenyl complex which undergoes dehydrogenation.In addition, both FeCH3⁺ and CoCH3⁺ appear to insert into ethyne, generating a vinyl species which dehydrogenates to form MC3H3⁺.These results suggest the following order for methyl migratory insertation into C-C multiple bonds: butadiene ca. ethyne > ethene.Decomposition of M(C5H9)⁺ species proceeds by initial skeletal rearrangement to a linear structure followed by dehydrocyclization to generate M-c-C5H5⁺.A stable Co(pentadienyl)⁺ species was generated and is distinguishable from the corresponding Co(cyclopentyl)⁺ complex by H/D exchange with deuterium.Finally, D⁰(Fe⁺-pentadienyl) is found to exceed 70 +/- 6 kcal/mol and D⁰(Co⁺-pentadienyl) exceeds 62 +/- 5 kcal/mol.