We subsequently found that the combination of Pd(I) complex 6 and TEMPO led to an immediate colour change upon mixing and formed 5b in 97% yield (Scheme 6, b). The solid-state structure of 5b subsequently revealed this complex to be a Pd complex coordinated by TEMPO in an η 2 -N,O fashion, which has been observed in a few other cases and comparable to known η 2 -nitrosoarene adducts. The solid-state structure of 5a was similarly obtained, as illustrated in Figure , and an analogous Ad3P-coordinated complex S2 was isolated chromatographically and was crystallographically characterized (see Figure ). Each of these complexes is indefinitely stable under air at room temperature. Based on the similarity of Pd-N and Pd-O bond lengths (± 0.04 Å) and N-Pd-O bond angles (± 0.2°) in the reference compounds and 5a, 5b, and S2, we assign these structures as Pd(II) complexes. This is consistent with our hypothesis that a Pd(I) species forms as the immediate transition metal product following light-induced Pd(II)-C homolytic cleavage, which then undergoes rapid one-electron oxidation by the excess TEMPO present under these reaction conditions.