In many biological and synthetic systems, electron-transfer reactions by redox-active transition metals often function by participating with redox-inactive metals to facilitate reactivity, such as the potassium-promoted iron surfaces used in the Haber-Bosch process, or the Ca2+ ion in the oxygen evolving complex of photosystem II. Inclusion of these redox-inactive Lewis acids have been shown to enhance electron-transfer rates and tune reduction potentials in synthetic chemical systems, as well as facilitate H-H, N-N and O-O bond cleavage. In this work, we set out to design this feature into the redox non-innocent pyridinediimine (PDI) scaffold by synthesizing a family of Iron (II) pyridinediimine complexes with a 15-crown-5 ether moiety located in the secondary coordination sphere. This lead to a redox active metal-ligand complex with a Lewis acid in secondary sphere, as these pockets are perfectly sized to house metal ions such as Na+. We report here the synthesis and characterization of these complexes, including NMR analysis of the effect of binding Na+ in the pocket as well as electrochemical studies, which have demonstrated that these complexes exhibit modest shifts in the reduction potential of the metal-ligand scaffold upon encapsulation.

Iron (II) pyridinediimine complexes with Lewis acids in the secondary coordination sphere

253rd National Meeting (2017)

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