In the presence of Fe+ catalyst, the retro Diels-Alder reaction of norbornadiene (NBD) is predicted to be stepwise, with an activation barrier of 18.8 kcal/mol, which is 3.1 kcal/mol lower than the concerted retro reaction. For norbornene (NBN), the Fe+-catalyzed retro reaction is also calculated to be stepwise with an activation barrier of 24.9 kcal/mol, which is 8.5 kcal/mol lower than the uncatalyzed stepwise reaction but 3.8 kcal/mol higher than the concerted reaction. The intermediates from the NBD and NBN retro Diels-Alder reactions, C5H6FeC2H2+ and C5H6FeC2H4+, are predicted to have low activation barriers for ligand-to-ligand hydrogen transfers (through an iron-hydrido intermediate) to form CpFeC2H3+ and CpFeC2H5+ and, ultimately, vinyl- and ethyl-substituted cyclopentadiene-iron complexes, respectively. In contrast to FeC2H2+ and FeC2H4+, the lowest-energy pathways on the C5H6FeC2H2+ and C5H6FeC2H4+ potential energy surfaces involve only one multiplicity (quartet). The C2H2 and C2H4 complexes of CpFe+ and C5H6Fe+ are compared.