Fluxional behavior of iron complexes of 1,2-cycloheptadiene: The role of the allyl cation

Article abstract of DOI:10.1021/om00100a014

The fluxional behavior of two iron complexes of 1,2-cycloheptadiene - (η⁵-C₅H₅)(CO)₂Fe(η ²-1,2-cycloheptadiene)fluoroborate (5) and its Ph₃P-substituted relative 13 - has been studied. At this time, we report evidence for (1) fluxionality of 5 by a Vrieze-Rosenblum mechanism (E_a = 13.9 kcal/mol), a mechanism where the chirality of the allene moiety is retained, (2) fluxionality of 13 by the same mechanism with an activation barrier about 3-4 kcal/mol higher than that for 5, (3) accessibility of an allyl cation mechanism in the latter case with E_a = ca. 23 kcal/mol, and (4) circumstantial evidence for accessibility of an allyl cation (E_a between 14.2 and 22 kcal/mol) from 5.