Despite the success of iron-based catalysts for cross-coupling, a detailed molecular level understanding of these systems has remained elusive. This limitation is in stark contrast to palladium chemistry, where detailed studies of active catalyst structure and mechanism have provided the foundation for the continued design and development of catalysts with novel and/or improved catalytic performance. The use of an experimental approach combining advanced inorganic spectroscopies (Mössbauer, magnetic circular dichroism, electron paramagnetic resonance), density functional theory studies, synthesis and kinetic analyses enables the direct evaluation of the active iron species and insight into the mechanisms of catalysis in iron catalyzed cross-coupling. Previous studies from our group using this approach have established the active iron species in iron-bisphosphine catalysed cross-coupling of mesityl Grignard and primary alkyl halides as well as phenyl nucleophiles and secondary alkyl halides. Of particular interest are iron-catalyzed cross-couplings with simple ferric salts where we have previously reported the isolation and characterization of [MgCl(THF)5][FeMe4], an intermediate in the reduction pathway of simple ferric salts with methylmagnesium bromide. This presentation will focus on recent studies, including the isolation, characterization and reactivity of iron-ate species of relevance to cross-coupling such as [MgCl(THF)5][Fe8Me12], as well as recent developments in systems combining iron salts and ligand additives.

Iron-catalyzed cross-coupling: Intermediates and mechanism

254th National Meeting (2017)

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