Given the high synthetic potential of C–H bond functionalization strategies, it is critical to establish the key features necessary for such reactivity so as to enable rational catalyst design. Towards this end, our group has previously reported C–H amination catalysis using high-spin iron dipyrrinato complexes, ascribing this reactivity to the unique electronic configuration of an isolated putative intermediate: a high-spin ferric center antiferromagnetically coupled to an iminyl radical. Using a sterically accessible tert-butyl substituted dipyrromethene scaffold, an analogous species (tBuL)FeCl(●NC6H3-2,6-iPr2) was identified, establishing the inherent preference of the dipyrrin iron systems for such an unusual electronic construct. Paring down the steric profile around the nitrogen atom, however, promotes formation of a di-iron bridging imido [(tBuL)FeCl]2(μ-NC6H3-3,5-(CF3)2). Notably, despite its diamagnetic ground state, the bridging imide can successfully transfer the N-group into allylic and benzylic C–H bonds under stoichiometric and catalytic conditions. Both dissociation into an iron iminyl and an unprecedented hydrogen atom abstraction directly from the bridging imide are viable routes for the C–H activation step. Understanding the electronic structure considerations in our systems permitted us to systematically tune the iron dipyrrin complexes to develop catalysts for more controlled C–H amination processes.

High-spin iron complexes for C–H amination: from electronic structure to catalysis

256th National Meeting (2018)

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