Protonation of homotroponeiron tricarbonyl and cyclooctatrienoneiron tricarbonyl complexes

2,3-Homotroponeiron tricarbonyl, 8-methyl- and 8,8-dimethyl-2,3-homotroponeiron tricarbonyl complexes have been shown to undergo O-protonation in trifluoroacetic (TFA) and 96% sulfuric acids. In the latter acid the O-protonated cations rearrange to give the thermodynamically more stable C-protonated isomers. Cyclooctatrienoneiron tricarbonyl undergoes protonation H2SO4 to give the same cation as was obtained from the protonation of the homotroponeiron tricarbonyl complex in H2SO4. On the basis of reaction in D2SO4, it is suggested that the kinetically preferred site of protonation of the cyclooctatrienone complex is at C(2) one of the coordinated carbon atoms.