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

Article abstract of DOI:10.1016/0022-328X(89)85345-8

Reaction of the cyclopentadienyliron (CpFe) complex of o-, m- or p-dichlorobenzene (Ia, Ib or Ic, respectively) with an excess of n-butylamine gave only monosubstitution of one of the two chloro groups, while a similar reaction carried out in the presence of some added HOAc resulted in disubstitution of both chloro groups.On the other hand, in the reaction of Ia, Ib or Ic with one equivalent or with an excess of pyrrolidine, respectively, mono- or disubstitution took place.These observations support the previous 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, while for a reaction with a secondary amine, there could be no deprotonation with the monosubstitution product, thus allowing disubstitution to occur.When Ia, Ib or Ic are reported with an excess of NaCN in DMF for up to 4 days, only monosubstitution was observed, a pure product being obtained with Ia, while with Ib or Ic, the product was contaminated with a large amount of starting material.When the same reaction of Ia, Ib or Ic with NaCN was carried out for 30 min and then worked up without any added aqueous NH4PF6, cyclohexadienyl complexes from the nucleophilic addition of a cyanide ion were obtained.Under similar reaction conditions but with the reaction time extended for 2 days, Ia could also give rise to products derived from monosubstitution and cyanide addition.Mechanistic implications of these results are discussed.