THE REACTION OF THE [CPFE(CO)(2)](-) ANION WITH PENTAFLUOROCHLOROBENZENE - NUCLEOPHILIC AROMATIC-SUBSTITUTION BY HALOGEN-METAL EXCHANGE

In the reaction of the [CpFe(CO)(2)](-) anion with pentafluorochlorobe nzene, [CpFe(CO)(2)](2) and p-chloroperfluoropolyphenyls C6F5(C6F4)(n) -C6F4Cl (n=0-3) are formed alongside the expected chlorine substitutio n product [C6F5Fe(CO)(2)Cp]. The relative yield of these products depe nds on the ratio of initial reactants, solvent (THF ether, DMSO, MeCN) , counterion (K+, K(+)18-crown-6, [(C6H5)(3)P=N=P(C6H5)(3)](+) [PPN+]) and temperature. The highest yield of [C6F5Fe(CO)(2)Cp] (approximate to 50%) was obtained in THF, with a slight excess of pentafluorochloro benzene added to [CpFe(CO)(2)]K at room temperature. In the presence o f proton donors rBuOH or PhCH(Et)CN the reaction does not yield [C6F5F e(CO)(2)Cp] and p-chloroperfluoropolyphenyls at all; instead C6F5H and [CpFe(CO)(2)](2) are formed. This fact and other data point to the [C 6F5](-) anion as the key intermediate in all of the observed transform ations, among them the formation of [C6F5Fe(CO)(2)Cp]. The evidence fr om the use of radical traps (R2PH and PEt3) indicates that free radica ls are not involved in the major reaction pathway. Halogen-metal excha nge is proposed as the first step of the reaction mechanism. The subse quent competition between the possible reactions of the exchange inter mediates, [CpFe(CO)(2)Cl] and [C6F5](-), is discussed to account for t he highly variable ratio of the final products.