Experimental Determination of Primary and Secondary Deuterium Isotope Effects in the FeI-Mediated CH/CC Bond Activation of [Fe(4-Heptanone)]⊕ Complexes in the Gas Phase

Abstract

The gas-phase behaviour of [Fe(4-heptanone)]^⊕ is in several aspects quite distinct from that of other Fe^⊕ complexes as far as kinetic details of the individual steps of CH/CC bond activation are concerned. From the study of intramolecular kinetic isotope effects the following is concluded: (i) In the production of molecular hydrogen, it is the reductive elimination which is subject to a relatively large isotope effect (k_H2/k_HD = 2.70); in contrast, β-hydrogen transfer is associated with a small one (k_H/k_D = 1.05). (ii) For ethylene loss, both the β-CC bond cleavage and the olefine detachment are affected by substitution of deuterium for hydrogen (k_H/k_D = 1.14 and k_H/k_D = 1.11, respectively). (iii) The rate-initiating step, i. e. insertion of the (complexed) Fe^⊕ into a CH bond, is not subject to a discernible isotope effect.