A halogenophilic pathway in the reactions of transition metal carbonyl anions with [(η~6-iodobenzene)Cr(CO)_3]

摘要

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 [(η~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* = η~5-C_5Me_5) results in nucleophilic substitution to give [(η~6-C_6H_5FeCp*(CO)_2)Cr(CO)_3]. Reaction with Na[Re(CO)5] quantitatively gives the iodo(acyl)rhenate anion Na[(η~6-C_6H_5C(O)ReI(CO)4)Cr(CO)_3] and in the case of K[Mn(CO)5] a mixture of σ-aryl complexes [(η~6-C_6H_5Mn(CO)_5)Cr(CO)_3] and K[(η~6-C_6H_5Mn-(CO)_4I)Cr(CO)_3]. An analogous rhenium complex Na[(η~6-C_6H_5Re(CO)_4I)Cr(CO)_3] is formed from the initial iodo(acyl)rhenate upon prolonged standing at 20 °C, and its structure (in the form of [NEt4]~+ salt) is established by X-ray diffraction analysis. The reaction of [(η~6-chlorobenzene)Cr(CO)_3] with K[CpFe(CO)_2], in contrast, proceeds by the common S_N2Ar mechanism.