In Crystallo Snapshots of Rh2-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 in crystallo synthesis of Rh-2 nitrenoids that participate in catalytic C-H amination, and we characterize these transient intermediates as triplet adducts of Rh-2. Further, we observe the impact of coordinating substrate, which is present in excess during catalysis, on the structure of transient Rh-2 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.