Isolation and characterization of a tetramethyliron(III) ferrate: an intermediate in the reduction pathway of ferric salts with MeMgBr.

While iron-catalyzed Kumada cross-coupling reactions with simple iron salts have been known since the early 1970s, the nature of the in situ-formed iron species remains elusive. Herein, we report the synthesis of the homoleptic tetralkyliron(III) ferrate complex [MgCl(THF)5][FeMe4] from the reaction of FeCl3 with MeMgBr in THF. Upon warming, this distorted square-planar S = (3)/2 species converts to the S = (1)/2 species originally observed by Kochi and co-workers with concomitant formation of ethane, consistent with its intermediacy in the reduction pathway of FeCl3 to generate the reduced iron species involved in catalysis.