MECHANISTIC ASPECTS OF THE REACTION OF ANIONIC IRON(0)-OLEFIN COMPLEXES WITH ORGANIC HALIDES - DETECTION AND CHARACTERIZATION OF PARAMAGNETIC ORGANOMETALLIC INTERMEDIATES

The scope and the mechanism of the reactions of [CpFe(COD)][Li(TMEDA) (Cp = C5H5-; COD = 1,5-cyclooctadiene; TMEDA = Me(2)NCH(2)CH(2)NMe(2)), 1, with a number of organic monohalides and geminal dihalides were investigated. With monohalides organic coupling products were observed, and, in:particular, the coupling and cross-coupling of benzyl and allyl halides were studied in detail. The addition of 1 equiv of benzyl halide to 1 in benzene resulted in the initial formation of [CpFe(COD)(CH(2)Ph)], 7. The predominant pathway involved an initial one-electron transfer from [CpFe(COD)](-) to PhCH(2)X to form PhCH(2)X*(-) and [CpFe(COD)]*. PhCH(2)X*(-) quickly disproportionated to form PhCH(2)* and X(-). The benzyl radical then added to [CpFe(COD)]*. Once formed [CpFe(COD)(CH(2)Ph)] reacted with TMEDA in a disproportionation reaction to form 0.5 equiv of the paramagnetic compound, [(TMEDA)Fe(CH(2)Ph)(2)], 3, and 0.5 equiv of FeCp(2). When additional benzyl (or allyl) halide was added, it reacted with [(TMEDA)Fe(CH(2)Ph)(2)] to form the coupled (or cross-coupled) product. This coupling reaction involved the intermediacy of benzyl (and allyl) radicals, and the experimental results were consistent with the product being formed by the coupling of two radicals in solution.