A halogenophilic pathway in the reactions of transition metal carbonyl anions with [(η⁶-iodobenzene)Cr(CO)₃].

The paper provides the first example of formal nucleophilic substitution by the halogenophilic pathway in Cr(CO)(3) complexes of haloarenes with metal carbonyl anions. All metal carbonyl anions examined attack [(eta(6)-iodobenzene)Cr(CO)(3)] at halogen, which is shown by aryl carbanion scavenging with t-BuOH. The reaction with K[CpFe(CO)(2)] gives only the dehalogenated arene, but the reaction with K[Cp*Fe(CO)(2)] (Cp* = eta(5)-C5Me5) results in nucleophilic substitution to give [(eta(6)-C6H5FeCp*(CO)(2))Cr(CO)(3)]. Reaction with Na[Re(CO)(5)] quantitatively gives the iodo(acyl)rhenate anion Na[(eta(6)-C6H5C(O)ReI(CO)(4))Cr(CO)(3)] and in the case of K[Mn(CO)(5)] a mixture of sigma-aryl complexes [(eta(6)-C6H5Mn(CO)(5))Cr(CO)(3)] and K[(eta(6)-C6H5Mn(CO)(4)I)Cr(CO)(3)]. An analogous rhenium complex Na[(eta(6)-C6H5Re(CO)(4)I)Cr(CO)(3)] is formed from the initial iodo(acyl)rhenate upon prolonged standing at 20 degrees C, and its structure (in the form of [NEt4](+) salt) is established by X-ray diffraction analysis. The reaction of [(eta(6)-chlorobenzene)Cr(CO)(3)] with K[CpFe(CO)(2)], in contrast, proceeds by the common S(N)2Ar mechanism.