exo/endo-Selectivity in the Reaction of 'Bare' FeO+ with Bicycloheptane (Norbornane)

Article abstract of DOI:10.1002/hlca.19950780423

'Bare' FeO⁺ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to ⁺ (32 percent), ⁺ (19 percent), ⁺ (19 percent), and ⁺ (14 percent), which are structually characterized by ligand exchange as well as collision-induced dissociation experiments.Circumstantial evidence is provided which indicates that the complexes ⁺, ⁺, and ⁺ originate from an Fe(norbornene)⁺ intermediate which itself is formed by elimination of H2O from the + encounter complex.Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the product ions clearly points to a preferential endo-attack of bare FeO⁺, with an endo/exo ratio of ca. 10.3 and kinetic isotope effects k_H/k_D for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C-H bond.The preferred endo-approach of bicyclo<2.2.1>heptane by 'bare' FeO⁺ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face.