The reactions of nitrosoarenes with cationic cyclohexadienyl complexes of iron tricarbonyl: an ESR study

The reactions of nitrosoarenes with the (cyclohexadienyl)Fe(CO) 3 cation have been investigated by using electron spin resonance spectroscopy. The radicals produced are nitroxides of the type (OC) 3 Fe(C 6 H 7 )(Ar)N—O• but, in some cases, disproportionation and loss of the metal carbonyl fragment leads to the corresponding C 6 H 5 (Ar)N—O• radical. With bulky nitrosoarenes, such as C 6 Me 5 NO, isomers are observed in which the aryl ring rotation is slow on the ESR time scale. The analogous reactions with the cyclohexadienyl cation derived from the B ring of (ergosteryl acetate)Fe(CO) 3 lead to initial attack not at one of the termini of the delocalized system but rather at the central carbon, i.e., at C-7. Subsequent hydrogen migration leads to the (5,7-diene)Fe(CO) 3 complex bearing the arylnitroxide at the 7-position. The mechanisms of these reactions are discussed. Keywords: nitrosoarenes, iron cations, ESR.