The Reaction of Haloferrocenes with Copper (I) Salts in Pyridine

The halogen exchange reaction of haloferrocene series with copper(I) salts (halide, cyanide) in an organic base was studied in comparison with that of the halobenzene series, which is regarded as a kind of nucleophilic substitution. Chloro-, bromo-, and cyanoferrocene were all obtained from iodoferrocene by this reaction in good yields. The reactivity of the ferrocene series was much higher than that of the benzene series. The order of the reactivity of halogen, I>Br>Cl, was similar to that of the benzene series. On the other hand, the substituent effects in the comparative reactivity of 1’-substituted-1-chloroferrocene with copper(I) cyanide was observed to be as follows: Et>H>Cl>Ac. This order in the ferrocene series was opposite to that in the p-substituted bromobenzene series: CN>Ac>Br>H>Me. In view of the electrophilic tendency in the ferrocene series and its high reactivity, the reaction mechanism is discussed.