Studies on some mono- and di-substitution reactions with cyclopentadienyliron complexes of o-, m- and p-dichlorobenzenes

Reaction of the cyclopentadienyliron (CpFe) complex e.g. I-III with an excess of BuNH2 gave only monosubstitution of one of the two chlorogroups, whereas a similar reaction carried out in the presence of some added HOAc resulted in disubstitution of both chloro groups. However, in the reaction of I-III with one equiv. or with an excess of pyrrolidine, resp., mono- or di-substitution took place. These observations support the previous (Lee, C., et al., 1986) suggestion that, under the basic conditions of the reaction, deprotonation of the monosubstitution product from a reaction with a primary amine would render the second chloro group incapable of undergoing another nucleophilic substitution, whereas for a reaction with a secondary amine, there could be no deprotonation with the monosubstitution product thus allowing disubstitution to occur. When I-III was treated with an excess of NaCN in DMF for up to 4 days, only monosubstitution was obsd., a pure product being obtained with I whereas with II or III, the product was contaminated with a large amt. of starting material. When the same reaction of I-III with NaCN was carried out for 30 min and then worked up without any added aq. NH4PF6, cyclohexadienyl complexes from the nucleophilic addn. of a cyanide ion were obtained. Under similar reaction conditions but with the reaction time extended to 2 days, I could also give products derived from monosubstitution and cyanide addn. Mechanistic implications of these results are discussed.