Abstract
A study of ferrocenyl ketones in CDCl 3/SO 2/FSO 3H solution at low temperature has shown that these protonated ketones are excellent NMR models for the corresponding ferrocenylcarbinyl cations. Comparison of the results of a similar study of tricarbonyl( trans,trans-dienone)iron complexes to the limited NMR data available for the corresponding tricarbonyl ( trans-π-pentadienyl)iron cations suggests strongly that the protonated ketones are good models for the latter cations also. A qualitatively similar pattern of downfield NMR shifts as that observed on protonation of dienone-Fe(CO) 3 complexes is caused by oxidation of dienol-Fe(CO) 3 complexes to dienone-Fe(CO) 3 complexes. These data are interpreted as favoring a conjugative mechanism for stabilization of ferrocenylcarbinyl and tricarbonyl ( trans-π-pentadienyl)iron cations as opposed to one involving neighboring group participation by iron. Owing to exchange with free fluorosulfonic acid, NMR signals for hydrogens on carbonyl oxygen were not observed.
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