Snapshots of Rh-Catalyzed C-H Amination.

While X-ray crystallography routinely provides structural characterization of kinetically stable pre-catalysts and intermediates, elucidation of the structures of transient reactive intermediates, which are intimately engaged in bond-breaking and -making during catalysis, is generally not possible. Here, we demonstrate synthesis of Rh nitrenoids that participate in catalytic C-H amination, and we characterize these transient intermediates as triplet adducts of Rh. Further, we observe the impact of coordinating substrate, which is present in excess during catalysis, on the structure of transient Rh nitrenoids. By providing structural characterization of authentic C-H functionalization intermediates, and not kinetically stabilized model complexes, these experiments provide the opportunity to define critical structure-activity relationships.