Alkyl radical addition to (η 6 -arene)tricarbonylmangenese complexes was investigated with SmI 2 , zinc, or indium as the radical initiator. Among them, the indium-mediated reactions of (η 6 -arene)tricarbonylmangenese cations with various alkyl iodides in aqueous media afforded the corresponding radical addition-reduction products in moderate to excellent yields.Complexation of an arene ring with a Cr(CO) 3 or Mn-(CO) 3 + moiety significantly reduces the electron density of the arene ring, thus allowing nucleophilic addition to occur. 1 The reduction of the electron density of the phenyl ring also encourages the addition of nucleophilic radicals. 2 For example, Merlic and co-workers demonstrated that ketyl radical addition to Cr(CO) 3 -complexed benzene is at least 100 000 times faster than attack on free benzene. 3 However, only a few examples were reported on radical addition to arene-metal complexes, most of which dealt with ketyl radical addition to (η 6 -arene)Cr(CO) 3 complexes. 3-5 Recently, we reported the first examples of radical addition to (η 6 -arene)tricarbonylmangenese cations (1) by reaction with alkylmercury halides. 5c The alkyl radical added to the phenyl ring in 1 to generate the corresponding 17-valence electron intermediate, which was presumably further reduced by alkylmercury halide, leading to the formation of the stable 18-valence-electron product 2 and to the regeneration of an alkyl radical. 6 In this reaction the alkylmercury halide served not only as the radical precursor but also as the reducing agent. This radical chain process worked well for tert-butylmercury halide, and an excellent yield of the product 2a was achieved. However, with isopropylmercury halide the chain process was less efficient, while almost no reaction could be observed for isobutyl-or n-butyl-mercury halide. Moreover, the high toxicity of alkylmercury halides also limited the application of the above method in organic synthesis. To develop general and convenient methods to conduct the radical reactions, we carried out the following investigation. We report here that alkyl radical addition to (η 6 -arene)Mn(CO) 3 + complexes can be successfully carried out in aqueous media by reaction with indium(0) and alkyl iodides. Results and DiscussionAs discussed above and also in the literature, 2,5c successful radical addition to arene-Mn(CO) 3 + complexes would require both a radical precursor and a reducing agent. A metal reductant and an alkyl halide would be an ideal combination to meet this requirement. Thus, we chose manganese complex 1a as the model substrate and isopropyl iodide as the radical source to explore this possibility (eq 1). The results are presented in Table 1.Treatment of an alkyl iodide with SmI 2 to generate an alkyl radical is well documented. 7 Thus, we first tested the SmI 2 /i-PrI system. The reaction of 1a with .(1) For reviews, see: (a) Kane-Maguire, L. A. P.; Honig, E. P.; Sweigart, D. A.