The activation of metal-halide bonds is central to solar energy storage and to the development of methodologies for photoredox-mediated activation of C-H bonds in organic synthesis. Halogen radicals have long been known to activate hydrocarbon C–H bonds in classical reactions such as free radical halogenations, while recent work has highlighted the utility of photogenerated radicals as C–H abstraction agents. For example, reports on photocatalytic Ni-catalyzed C–H arylation have proposed that halogen radicals mediate the C–H activation step in these reactions. We developed coordination complexes that poise these molecules ahead of their most reactive state, and then we exposed them to 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 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 could tune the secondary coordination sphere in all directions; in turn this allowed us to modify the electronic properties of the metal by changing the R-group at the 4-position of the pyridine ring, and thus the amount of room available in the lattice required for halide elimination. This enabled the study of the photoreactivity of these compounds both in the solid state and in solution.

Caught in the act: Capturing C–H bond activation with photocrystallography

2019 Fall National Meeting

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