Mimicking the Namesake Reaction of Extradiol Catechol Dioxygenase on Iridium

Extradiol catechol dioxygenases expand a benzenediol (catechol) by oxygen atom insertion, generating the corresponding seven-membered oxepinedione. Because the enzymes accept any of the MnII, FeII, or CoII as metallocofactors, each state derived from FeII may have one-electron-shifted analogs. Here, we observe the conversion of a synthetic Ir-peroxo (2) to three complexes – 3, 4, and 5 – models for several previously hypothesized intermediates. An H• can be abstracted from 2 to furnish the metallatrioxolane 3, which is one-electron reduced from the more widely characterized FeII intermediate. Alternatively, photolysis of 2 (467 nm) results in 4, from which an H• can be abstracted to generate 5. Both 4 and 5 are oxepinedione products that remain bound to Ir. The X-ray structure of 5 features a κ2-bound, dianionic ortho ester – a motif which has no prior analogy. These unusual states were made synthetically accessible by incorporating a catechol-like substrate into a multidentate ligand framework.