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

Abstract

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 [(η⁶-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* = η⁵-C₅Me₅) results in nucleophilic substitution to give [(η⁶-C₆H₅FeCp*(CO)₂)Cr(CO)₃]. Reaction with Na[Re(CO)₅] quantitatively gives the iodo(acyl)rhenate anion Na[(η⁶-C₆H₅C(O)ReI(CO)₄)Cr(CO)₃] and in the case of K[Mn(CO)₅] a mixture of σ-aryl complexes [(η⁶-C₆H₅Mn(CO)₅)Cr(CO)₃] and K[(η⁶-C₆H₅Mn(CO)₄I)Cr(CO)₃]. An analogous rhenium complex Na[(η⁶-C₆H₅Re(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 [(η⁶-chlorobenzene)Cr(CO)₃] with K[CpFe(CO)₂], in contrast, proceeds by the common S_N2Ar mechanism.