The activation of metal-halide and metal-oxygen bonds from first-row transition metal complexes is central to solar energy storage and to the development of methodologies for photoredox-mediated activation of C-H bonds in organic synthesis. We seek to develop mono- and bimetallic coordination complexes that poise molecules ahead of their most reactive state, and then use light to transiently generate reactive intermediates that can be spectroscopically and structurally characterized without isolation. Such characterization is a useful prerequisite to iteratively improve catalyst design and efficiency.<br/> <br/>We present a study of metal-halide and metal-oxygen bond activation with the use of mono-metallic iron pyridine diimine (PDI) systems. The PDI  ligand is not only redox non-innocent but its secondary coordination sphere is easily engineered to assist photoreactivity. With these ligands, we are able to tune the metal–metal distance, the electronic properties of the metal by changing the R-group at the 4-position of the pyridine ring, and the rigidity of the scaffold. For metal-halide bond activation, monometallic centers are used whereas for metal-oxygen bond activation a cofacial bimetallic system is used. Physically linking the two metal centers allows for the metal–metal distance to be constrained, preventing the system from relaxing to a more stable and less reactive state. This constraint is realized in biology through a protein matrix, and in zeolites by means of an extended lattice, and allows for the formation of sterically crowded and reactive intermediates. In our work we achieve such a constraint using bis–pyridine diimine ligands that allow for two metals to sit in a cofacial arrangement in identical chelated environments. With these ligands, we are able to tune the metal–metal distance, the electronics at the metal by changing the R-group at the 4-position of the pyridine ring, and the rigidity of the scaffold. All these parameters can thus be utilized to probe and optimize systems for small molecule activation.<br/>

Using mono- and bimetallic pyridine diimine scaffolds to study transient reactive intermediates

256th National Meeting (2018)

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